 DRAFT U GANDA STANDARD  
  DUS 2021  
First Edition  
2019-04-24 
 
 
 Reference number  
WDUS 2021 :2018 
© UNBS  2018   
  
Preservative  Treatment of T imber  
 WDUS 2021 :2019 
ii © UNBS 2018  – All rights reserved  
 Compliance with this standard does not, of itself confer immunity from legal obligations  
A Uganda Standard does not purport to include all necessary provisions of a contract. Users are 
responsible for its correct applica tion 
© UNBS 2019   
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The Executive Director  
Uganda National Bureau of Standards  
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Uganda  
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Fax: +256 41 4 286 123  
E-mail: info@unbs.go.ug  
Web: www.unbs.go.ug  DUS 2021 :2019 
© UNBS 2021  – All rights reserved  iii 
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ .............................  v 
The preservative trea tment of timber  ................................ ................................ ................................ ...............  1 
1 scope  ................................ ................................ ................................ ................................ ................................  1 
2 Normative references  ................................ ................................ ................................ ............................  1 
3 Terms and Definitions  ................................ ................................ ................................ ...........................  2 
4 Classification and properties of timber preservatives  ................................ ................................ ................  3 
4.1 Classification  ................................ ................................ ................................ ................................ ................  3 
4.2 Properties  ................................ ................................ ................................ ................................ ......................  4 
6 Preparation of timber for treatment  ................................ ................................ ................................ ...............  8 
6.1 General  ................................ ................................ ................................ ................................ ..........................  8 
6.2 Sorting  ................................ ................................ ................................ ................................ ...........................  8 
6.2.1 Species  ................................ ................................ ................................ ................................ .......................  8 
6.2.2 Dimensions  ................................ ................................ ................................ ................................ ................  8 
6.2.3 Timber defects  ................................ ................................ ................................ ................................ ...........  8 
6.3 Seasoning  ................................ ................................ ................................ ................................ .....................  8 
6.3.1 General  ................................ ................................ ................................ ................................ .......................  8 
6.3.2 Moisture content  ................................ ................................ ................................ ................................ ........  8 
6.3.3 Prevention of insect attack during seasoning  ................................ ................................ .......................  9 
6.3.4 Prevention of mould attack  ................................ ................................ ................................ ......................  9 
6.4 Surfac e preparation  ................................ ................................ ................................ ................................ ...... 9 
6.5 Shaping  ................................ ................................ ................................ ................................ .........................  9 
6.6 Incising  ................................ ................................ ................................ ................................ ..........................  9 
6.6.1 General  ................................ ................................ ................................ ................................ .......................  9 
6.6.2 Methods  ................................ ................................ ................................ ................................ ....................  10 
6.7 Stacking  ................................ ................................ ................................ ................................ .......................  10 
7 Preparation and control of preservative mixtures  ................................ ................................ .....................  10 
7.1 General  ................................ ................................ ................................ ................................ ........................  10 
7.2 Mass concentration  ................................ ................................ ................................ ................................ .... 10 
7.3 Toxicity and safety  ................................ ................................ ................................ ................................ ..... 10 
7.4 Flammability  ................................ ................................ ................................ ................................ ................  10 
8 Application methods for preservatives  ................................ ................................ ................................ ....... 11 
8.1.1 Surface brushing and  spraying  ................................ ................................ ................................ .............  11 
8.1.2 Immersion, steeping, deluging  ................................ ................................ ................................ ..............  11 
8.2 Prescribed timber -preservative treatment processes  ................................ ................................ ............  11 
8.2.1 General  ................................ ................................ ................................ ................................ .....................  11 
8.2.2 Diffusion  ................................ ................................ ................................ ................................ ...................  11 
8.2.3 Gas phase process ................................ ................................ ................................ ................................ .. 12 
8.2.4 Hot or cold open tank process  ................................ ................................ ................................ ...............  12 
8.2.6 Low -pressure process  ................................ ................................ ................................ ............................  13 
8.2.7 The vacuum impregnation (double vacuum) process  ................................ ................................ .........  14 
8.3 Equipment required  ................................ ................................ ................................ ................................ .... 14 
9 Handling and safety of preservative -treated timber  ................................ ................................ ..................  15 
9.2 Safety  ................................ ................................ ................................ ................................ ...........................  15 
9.3 Fixation of WCCA preservatives  ................................ ................................ ................................ ...............  15 
9.4 Disposal  ................................ ................................ ................................ ................................ .......................  15 
9.5 Flammability  ................................ ................................ ................................ ................................ ................  15 
9.6 Safety handling information labelling  ................................ ................................ ................................ ...... 16 WDUS 2021 :2019 
iv © UNBS 2018  – All rights reserved  
 10 Penetration and net retention  ................................ ................................ ................................ ....................  16 
11 Recommendations for the use of timber preservatives in specific applications  ................................  24 
11.1 Contact with food ................................ ................................ ................................ ................................ ..... 24 
11.1.1 Direct contact with food for human consumption  ................................ ................................ ............  24 
11.1.2 Direct contact with feeds for livestock  ................................ ................................ ...............................  24 
11.1.3 Indirect contac t with food or feeds  ................................ ................................ ................................ ..... 24 
11.2 Human contact  ................................ ................................ ................................ ................................ .........  24 
11.3 Animal contact  ................................ ................................ ................................ ................................ .........  24 
11.3.1 Continuous direct contact  ................................ ................................ ................................ ...................  24 
11.3.2 Periodic direct contact  ................................ ................................ ................................ .........................  25 
11.4 Contact with plants  ................................ ................................ ................................ ................................ .. 25 
11.5 Combustion gases  ................................ ................................ ................................ ................................ ... 25 
11.6 Timber for use in cooling towers  ................................ ................................ ................................ ...........  25 
12 The use of preservative -treated timber in specific a reas in Uganda . a................................ .................  25 
12.1 Qualification  ................................ ................................ ................................ ................................ .............  25 
12.2 Gymnospermae (coniferous species)  ................................ ................................ ................................ ... 25 
12.3 Angiospermae (broadleaved species  ................................ ................................ ................................ .... 25 
12.4 Preservative treatment  ................................ ................................ ................................ ............................  26 
13 Treatment plant area compliance  ................................ ................................ ................................ ..............  26 
Bibliography  ................................ ................................ ................................ ................................ .....................  49 
 DUS 2021 :2019 
© UNBS 2021  – All rights reserved  v 
 Foreword  
Uganda National Bureau of Standards (UNBS) is a parastatal under the Ministry of Trade , Industry and 
Cooperatives established under Cap 327 , of the Laws of Uganda , as amended .  UNBS is mandated to co -
ordinate the elaboration of standards and is  
(a) a member of International Organisation for Standardisation (ISO) and  
(b) a contact point for the WHO/FAO Codex Alimentarius Commission on Food Standards, and  
(c) the Nation al Enquiry Point on TBT  Agreement  of the World Trade Organisation (WTO).  
The work of preparing Uganda Standards is carried out through Technical Committees. A Technical 
Committee is established to deliberate on standards in a given field or area and consis ts of key stakeholders 
including government, academia, consumer groups, private sector and other interested parties.  
Draft Uganda Standards adopted by the Technical Committee are widely circulated to stakeholders and the 
general public for comments. The c ommittee reviews the comments before recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council.  
The committee responsible for this document is Technical Committee UNBS /TC 12, furniture.   DRAFT UGANDA STANDARD  DUS 2021 :2018 
 
© UNBS 2018  – All rights reserved  1 
 The prese rvative treatment of timber  
1 scope  
This standard covers the classification of timber preservatives, hazard conditions for timber,  the solvents used 
for timber preservatives, the preparation of timber for treatment, the various  treatment processes and the  use 
of preservative -treated timber in specific areas in Uganda . Recommendations relating to the handling and 
safety of preservative -treated timber are also given.   This standard does not cover treatment with fire 
retardants . 
2 Normative references   
The fo llowing referenced documents referred to in the text in such a way that some or all of their content 
constitutes requirements of this document. For dated references, only the edition cited applies. For undated 
references, the latest edition of the referenc ed document (including any amendments) applies.  
DUS 1722 , Eucalyptus poles, cross -arms and spacers for power distribution and telephone  systems.  
DUS 2084, Heartwood detection in timber of pinus  species  
DUS 2018, Retention of preservative in timber (sample method).  
DUS 2013, Retention of preservative in timber (volume method)  
DUS 2019, Retention of preservative in timber (weighbridge method).  
DUS 2016, Moisture content of timber (electric moisture meter method)  
DUS 2014, Moisture content of timber and timbe r products (oven dry method)  
DUS 2015, Moisture content of timber (extraction method)  
DUS 2017, Depth of penetration of preservative and detection and depth of sapwood in timber  
US EAS 323 Specification for wood preservation by means of pressure creosotin g 
US EAS 324 Copper/chromium/arsenic compositions for the preservation of timber — Method for timber 
treatment  
 
 
 
 
 
  
2 © UNBS 2019 – All rights reserved  
 3 Terms and Definitions   
For the purposes of this document, the following terms and definitions apply  
 
3.1. 
acceptable  
acceptable to the a uthority administering this standard, or to the parties concluding the purchase  contract, as 
relevant  
 
3..2 
afterglow  
phenomenon where ignited timber keeps on glowing after having been set alight and after the  original source 
of ignition has been removed; this slow combustion could eventually lead to the total  destruction of the timber  
3..3 
average net retention  
<assay zone> mass of all active components of a preservative compound retained in the zone of  timber to be 
treated  
3..4 
average net retention  
<tota l volume> mass of all active components of a preservative compound (where relevant,  including water of 
crystallization) retained in the total volume (not the penetrated volume) of timber  
 
3.5 
bleeding  
exudation of liquid preservative chemical on a surface of preservative -treated timber  
3..6 
charge  
quantity of timber treated in one and the same treating cycle   
3..7 
inner bark  
physiologically active layer of tissues between the cambium and the phellogen, plus any cells of the  phloem 
that remain alive  
 
3..8 
marine treatment  
treatment of timber that will be constantly in contact with estuarine or sea water and therefore  subject  to 
marine borer attack  
 
3..9 
outer bark  
layer of dead tissues (generally of a dry corky nature) outside the phellogen  
3.10 
permanent bui lding  
structure in which people live, work or play or in which animals are accommodated or in which  goods are 
preserved, worked, manufactured, processed, stored or sold; as well as a bridge, cooling  tower, water tank 
tower, watch tower, pylon, water work  or similar structure for which a plan is to be  approved in terms of one or 
other provision in legislation before the construction  DUS 2021 :2019 
© UNBS 2018  – All rights reserved  3 
  
3.11 
structural timber  
all timber of the botanical group Gymnospermae (coniferous species and Angiospermae  (broadleaved specie s 
(see 12.3)), which forms part of a permanent building or which is destined to  form part of a permanent 
building, for example, but not limited to roof structures, frame -wall construction, flooring, paneling , window 
frames and door frames  
 
3.12 
timber -pres ervative treatment  
pesticidal agent that, when impregnated into or otherwise applied to timber, renders the timber less  
susceptible to destruction by fungi, insects or marine borers  
 
3..13 
timber protectant  
agent that is fungicidal or insecticidal or both,  and that is applied to timber to protect it temporarily  from attack 
during one or more stages of processing  
 
3.14 
volatile solvent  
timber -preservative solvent, at least 90 % of the volume of which evaporates from the treated opens tacked  
timber within an acceptable period after treatment  
3.2 
Abbreviations  
HCS hazardous chemical substance  
LOSP light organic solvent preservative  
MSDS material safety data sheet  
4 Classification and properties of timber preservatives  
4.1 Classification  
For the purposes of this  standard, timber preservatives1) are classified as shown in table 1.  
 
NOTE The determination of the class and type of a timber preservative is based on the chemical constitution  of the 
preservative components or of the treatment solution. Classification b ased on a qualitative analysis of  components present 
in the preservative or in the treated timber is possible in specific cases and should be  such as to be acceptable . 
 
Table 1 — Classification of timber preservatives  
1 2 3 
Class of  preservative  Type of  preservative  Description  
C CCHT  
CCL 
CCWO  Oil 
Creosote – High-temperature  
Creosote – Lurgi -gasification process  
Mixtures of creosote and waxy oil  
W WCCA  
WB 
WCuAz  Waterborne  
Mixtures of copper -chromium -arsenic compounds  Borate  
Mixtures of copper azole compo unds   
4 © UNBS 2019 – All rights reserved  
 O OB 
OTBTOL  
OTBTNP  
OZP Light organic solvent preservatives (LOSPs)  
Borate  
Tributyltin oxide -lindane  
Tributyltin napthenate -permethrin  
Azole -permethrin  
O OI-D LOSPs – Insecticides  
Deltamethrin  
   
 
 
 
4.2 Properties  
4.2.1 Class C: coal tar creosote an d timber preservatives with a coal tar creosote  basis . 
Class C consists of preservatives that contain distillates of coal tar, with or without a waxy oil  additive. The 
preservatives are complex mixtures of a large number of compounds, and certain  character istics are defined 
in the relevant standards . 
                                                      
 1) Timber protectants are not included in the table. See also the last paragraph of the introduction.  
 
Properties of preservatives of this class include th e following:   
a) the preservatives are normally resistant to leaching and are therefore particularly suitable for  exterior 
conditions (see 5(c) and (d)), and for interior work, except where their odour is  objectionable;  
b) the preservatives are not corrosi ve to metals but are highly flammable at normal treating  temperatures (see 
8.2.4, 8.2.5 and 9.5);  
 
c) no change in the dimensions or in the shape of timber results from creosote treatment;  
 
d) freshly creosoted timber cannot normally be painted; a bitumino us-based aluminium paint or  epoxy -based 
paint can be used on timber after it has been exposed for a few months, but other  paints can be applied only 
after some years of exposure;  
 
e) creosote is oily and dark in colour, and has a characteristic odour that can be absorbed by  foodstuffs and 
other materials in the vicinity without their actually coming into contact with the  creosoted timber;  
 
f) if applied to timber to a high retention, creosote is liable to bleed during the first few months after  
treatment, e specially during hot weather (if this would be objectionable, an empty -cell process is  
recommended (see 8.2.5.3 and 8.2.5.4)); and  
 
g) creosoted timber can stain plaster and other absorbent materials with which it comes into  contact.  
 
4.2.2 Class W: soluti ons of compounds in water  
 
4.2.2.1 General  
When required, timber treated with waterborne preservatives shall be re -dried before use.  
 
4.2.2.2 Type WCCA  
 
Type WCCA preservatives consist of a mixture of inorganic compounds that undergo chemical  changes in th e 
timber, becoming insoluble and leach resistant.  Properties of preservatives of this type include the following : 
 
a) the preservatives are suitable for interior and exterior use   DUS 2021 :2019 
© UNBS 2018  – All rights reserved  5 
 b) the preservatives are non -flammable;  
c) the preservatives cause corrosio n of certain metals, but treated timber, after a fixation period of  7 
days, is generally not corrosive;  
d) after having been re -dried  timber treated with these preservatives is odorless  and clean and, 
although slightly coloured, can be painted and glued;  
e) wetting and subsequent re -drying during treatment with these preservatives can cause grain  raising  and 
changes in the dimensions and the shape of the timber;  
f) the strength properties of a piece of timber are reduced as a result of the timber having bee n wetted during 
treatment with these preservatives; the normal working stresses assigned to a  specific grade are, however, 
not affected, although the use of wet timber in a load -bearing  application can lead to excessive deflection 
because of creep;  
 
g) aft er having been re -dried (see 4.2.2.1), timber treated with these preservatives is more  susceptible to 
damage by fire, because of afterglow, than is timber treated with a class C  preservative; and  
 
h) when timber that has been treated with these preservativ es is machined, faster blunting of tools  could be 
experienced compared to untreated timber . 
 
4.2.2.3 Type WB  
Type WB preservatives consist of a water -soluble inorganic borate such as disodium octaborate  tetra hydrate  
or a mixture of borax and boric acid. T imber treatment using preservatives of this type  can be carried out 
using a diffusion or a pressure process. Diffusion has to be carried out on green  timber (ideally, wet off saw) 
that has a moisture content of at least 400 g/kg at or near the timber  surfa ce and an average moisture content 
of at least 600 g/kg. When the pressure process is used,  seasoned timber has to be used. The pressure -
diffusion process (i.e. a combination of the pressure  and diffusion processes) can be used for the treatment of 
green o r semi -seasoned timber with  borate preservatives.  Properties of preservatives of this type include the 
following:  
a) the preservatives have a low mammalian toxicity;  
b) the preservatives are non -corrosive;  
c) the preservatives have a wide -spectrum activity  against fungi and insects;  
d) the timber colour is unaffected after treatment;  
e) the preservatives are odourless;  
f) wetting and subsequent re -drying during treatment with these preservatives can cause grain  raising  and 
changes in the dimensions and the shape of the timber;  
g) the strength properties of a piece of timber are reduced as a result of the timber having been  wetted during 
treatment with these preservatives; the normal working stresses assigned to a  specific grade are, however, 
not affected, al though the use of wet timber in a load -bearing  application can lead to excessive deflection 
because of creep; and  
h) owing to the water solubility of borates, these preservatives are only suitable for timber for  interior use, 
unless combined with an approp riate water -repellent system that can provide long  term protection against 
leaching when used in exterior above -ground H3 conditions.  
 
4.2.2.4 Type WCuAz  
 
Type WCuAz preservatives consist of mixtures of copper and azole biocides.  Properties of preservative s of 
this type include the following:  
 
a) the preservatives are suitable for interior and exterior use (see clause 11), with the exception of  marine 
applications;    
6 © UNBS 2019 – All rights reserved  
 b) the preservatives are non -flammable;  
c) the preservatives cause corrosion of yellow metal s, but treated timber, after a fixation period of  2 days, is 
generally non -corrosive;  
d) after ha ving been re -dried , timber treated with these preservatives is odorless  and clean, and although 
slightly coloured, can be painted and glued;  
e) wetting and sub sequent re -drying during treatment with these preservatives can cause grain  raising  and 
changes in the dimensions and shape of the timber;  
f) the strength properties of a piece of timber are reduced as a result of the timber having been  
wetted during treat ment with these preservatives; the normal working stresses assigned to a  specific grade 
are, however, not affected, although the use of wet timber in a load -bearing  application can lead to excessive 
deflection because of creep; and  
 g) after having been re -dried (see 4.2.2.1), timber treated with these preservatives is more  susceptible to 
damage by fire, because of afterglow, than is timber treated with a class C  preservative . 
 
4.2.3 Class O: solutions of organic compound(s) in organic solvents  
 
4.2.3.1 Typ es OTBTOL, OTBTNP and OZP  
 
The active agent commonly used in OTBTOL is tributyltin oxide -lindane; in the case of OTBTNP it is  tributyltin 
napthenate -permethrin, and in the case of OZP it is azole -permethrin. 1  
Properties of preservatives of these types i nclude the following:  
 
a) the preservatives are more resistant to leaching than are preservatives of type OB, but can be  subject to 
loss by evaporation; they are suitable for timber for interior use (see 5(e));  
b) the preservatives are usually non -staining  and non -corrosive;  
c) when the solvents have dried off after treatment, timber treated with these preservatives can  usually be 
painted and glued satisfactorily;  
d) the preservatives do not cause any raising of the grain or swelling of the timber and can t herefore  be used 
on machined timber without causing movement or distortion;  
e) where foodstuffs are to be located near to timber treated with these preservatives, special  precautions 
could be necessary to avoid contamination of the foodstuffs; and  
f) the s olvents are readily flammable and, until the solvents have evaporated, care should be taken  with timber 
treated with these preservatives.  
 
 
4.2.3.2 Type OB  
 
Type OB preservatives consist of a volatile organic borate (tri  methyl borate) that is applied to t he timber, 
under vacuum, in the gas phase. The active ingredient in this compound is boric acid, which  is common to the 
WB type preservatives.  Properties of preservatives of this type include the following:  
 
a) the preservatives have a low mammalian toxici ty; 
b) the preservatives are non -corrosive;  
c) the preservatives have a wide -spectrum activity against fungi and insects;  
d) the timber colour is unaffected after treatment;  DUS 2021 :2019 
© UNBS 2018  – All rights reserved  7 
 e) at the end of the treatment, the timber is clean and dry, and ready for immedia te use; and  
f) owing to the water solubility of borates, these preservatives are only suitable for timber for  interior 
use, unless combined with an appropriate water -repellent system that can provide long  term 
protection against leaching when used in exter ior above -ground H3 conditions.  
 
4.2.3.3 Type OI -D 
 
Type OI -D preservatives consist essentially of deltamethrin dissolved in an acceptable solvent.  eltamethrin is 
a single -purpose preservative that provides protection against insects only. If  protection is  also needed 
against attack by fungi, a broad -spectrum preservative should be used.  Properties of preservatives of this type 
are as given in 4.2.3.1, and the following:  
a) the preservative is only suitable for mouldings, ceilings, floorboards and joinery; and 
b) the preservative is usually non -corrosive, although tests have shown that the corrosion effect of  
type OI -D preservative on mild steel and galvanized steel fittings becomes more severe with  increase in 
retention.  
 
4.2.3.4 Organic solvents  
The solven t used with a class O preservative shall be as recommended by the preservative  manufacturer,  but 
should preferably be a volatile solvent. Where relevant, it may contain the  following additives:  
a) acceptable colour pigmentation for indicative or decorative  purposes; and  
b) an acceptable waxy oil to control excessive moisture content fluctuations.  
 
NOTE 1 A solvent may consist of one or more components.  
 
NOTE 2 Certain timber preservatives, for example lindane, are not soluble in aliphatic solvents.  
 
5 Class ification of hazard conditions for timber  
For the purposes of determining the level of preservative treatment required to ensure an  acceptable service 
life of timber, the hazard conditions under which timber is normally exposed to  attack by timber -destroyi ng 
agents are classified as follows:  
   
NOTE See clause 11 for specific applications and specific hazards.  
 
a) hazard class H6 (timber in sea water) : timber constantly or periodically in contact with  estuarine or sea 
water and therefore subject to marine b orer attack;  
b) hazard class H5 (timber in fresh water) : timber constantly or periodically in contact with fresh  water or 
heavy wet soils;  
c) hazard class H4 (timber in ground contact) : timber, interior or exterior, in direct or indirect  
contact with the g round;  
d) hazard class H3 (exterior timber above ground) : timber not in direct contact with the ground  but that will 
be exposed to leaching and weathering;  
e) hazard class H2 (interior timber above ground) : timber used under a roof, not in contact with  the ground, 
and that will not be exposed to weathering and leaching;  
f) hazard class H0 -i (single -purpose insecticides, specific end uses) : interior timber used for  moldings , 
ceilings, floorboards and joinery exposed to insect (excluding termites) attack only ; and 
g) hazard class H0 -it (single -purpose insecticides, specific end uses) : interior timber used for  moldings , 
ceilings, floorboards and joinery exposed to insect (including termites) attack only.  
  
8 © UNBS 2019 – All rights reserved  
 6 Preparation of timber for treatment  
6.1 General  
Before  treatment, timber should be selected with regard to its physical properties. The  recommendations 
given in 6.2 to 6.7 (inclusive) should be carefully followed if optimum results from  a treatment process are to 
be achieved. (See also 8.2.) To achieve the re commended  penetration  of preservatives, adequate sapwood 
depth is required. Do not preservative -treat timber that  contains inadequately cured glue lines. Timber that 
contains glue lines shall not be treated with a  class W preservative,   
 
 
6.2 Sorting  
6.2.1 Species  
Ensure that the timber treated in one charge has similar receptivity to treatment (see annex A) and  is of the 
same species. In the case of the Pinus genus, however, the timber does not have to be of  the same species .  
 
Do not mix hardwood and sof twood species in a charge, except when the  weighbridge method for 
retention determination is being used and when it is permitted in the relevant  product specification.  
  
 
6.2.2 Dimensions  
Unless the weighbridge method for retention determination is being u sed, ensure that the timber  treated in 
one charge is similar in form and dimensions, especially with regard to thickness. When  mixing of dimensions 
is unavoidable, treat to at least the average net retention given in table 3 for  the largest dimension in th e 
charge.  
 
NOTE In the context of this sub clause , each load in a charge may be considered as a separate charge if the  treatment schedule applied 
is that for the largest dimension of the timber that is most difficult to treat in any of  the loads and if the  average net retention of each load 
is determined.  
 
6.2.3 Timber defects  
Only treat timber that is free from decay, resinous patches, gum veins (other than veins that occur  below the 
required minimum depth of penetration), and from splitting that is more t han that specified  in the relevant 
product specification or by the purchaser . 
 
6.3 Seasoning  
6.3.1 General  
Except in the case of timber to be treated by the diffusion proc ess timber should be  seaso ned before 
preservative treatment . 
 
6.3.2 Moisture content  
 
6.3.2.1 Timber to be treated by the pressure process  
The  OR average moisture content of timber, determined in accordance with the appropriate of  DUS 2014, 
DUS 2015,DUS 2016  immediately before preservative treatment, shall be as  required in the relevant p roduct 
specification.   DUS 2021 :2019 
© UNBS 2018  – All rights reserved  9 
 In the case of timber products where drying defects such as warp and splitting are critical, it is  recommended 
that the average moisture content should not exceed 170 g/kg for class O  preservatives and 280 g/kg for class 
C and class W preservatives.  
 
 NOTE 1  Timber at these moisture contents, although satisfactory for treatment, should not necessarily be  considered as 
being properly seasoned timber . 
 
NOTE 2  The moisture content of timber treated using the gas phase process is dependen t upon timber  species and 
dimensions, but will not normally exceed 100 g/kg. Correct moisture content should be as  recommended by the 
preservative manufacturer . 
 
6.3.2.2 Timber to be treated by the diffusion process  
Timber to be treated by diffusion should  be freshly felled or wet off saw (   
6.3.2.3 Timber to be treated by the pressure -diffusion process  
No specific requirement is applicable in terms of moisture content of timber to be treated by  pressure -diffusion 
with diffusible preservatives of type WB, p rovided that the requirements for  penetration and retention are met . 
 
NOTE  Individual pieces of timber to be treated in the same charge should be of similar average moisture  content. The 
moisture content of individual pieces should not vary by more than 10 0 g/kg from the average  moisture content of the 
charge.  
 
6.3.3 Prevention of insect attack during seasoning  
Because the sapwood of hardwoods is generally susceptible to insect attack, untreated hardwoods  should be 
protected during seasoning and storage by the application of a suitable timber protectant.  
 
6.3.4 Prevention of mould attack  
Superficial mould tends to develop during seasoning before preservative treatment, as well as  during the 
closed -stacked phase following preservative treatment of timber with  borates by using  the diffusion process. A 
mouldicide should be applied to the timber during seasoning to prevent this,  or alternatively a mouldicide can 
be added to the borate solution.  
 
6.4 Surface preparation  
Only treat timber that is free from precipit ated water, dirt and other contaminating substances, and  free from 
rot and insect attack. Remove any outer and inner bark that can inhibit penetration.  Remove the bark by 
peeling or, where minor quantities of surface resin are present, by charring, in  both cases removing as little of 
the sapwood as possible. Patches of impenetrable resin or gum  scars or pockets may, depending on the type 
of timber product, be drilled or pierced to improve  penetration of the preservative. Use a centre -to-centre 
spacing of at  least 25 mm between holes,   which should not exceed 3 mm in diameter and 10 mm in depth .   
 
6.5 Shaping  
 Whenever practicable, perform all shaping and drilling before preservative treatment  
 
6.6 Incising  
6.6.1 General  
Incising is permissible when this has  been agreed upon between the treater and the purchaser of  the treated 
timber. Incising improves penetration in timber that is difficult to treat and reduces the  size of surface checks. 
Do not incise timber of nominal thickness less than 75 mm or faces of  softwoods that will be horizontal in use.  
  
10 © UNBS 2019 – All rights reserved  
 6.6.2 Methods  
Always make incisions approximately parallel to the general grain direction and to a depth equal to  that of the 
desired penetration (unless this adversely affects the strength of the timber). Space  incisions approximately 
25 mm apart in rows that are at an angle to the general grain direction and  that are approximately 60 mm 
apart and are such that incisions on the grain direction line are  spaced as far apart as possible. Achieve 
spacing such that the  number of incisions is approximately  650 per square metre . 
 
6.7 Stacking  
So stack timber in the treatment tank or cylinder that the preservative liquid has free access to all  faces of 
each piece (except in the case of sawn softwood timber, which can be tr eated as strapped  packages or 
bundles). Do not treat a unit or an assembly of units in its wrapping or packing. Where  relevant, ensure correct 
positioning of the samples for average net retention determination.    
 
NOTE  When planed timber is treated with a class O preservative, sticks or laths should be used to separate  each layer 
from the other . 
 
7 Preparation and control of preservative mixtures  
7.1 General  
Ensure that a preservative complies with the requirements of the relevant national standard given in  table 1.  
 
7.2 Mass concentration  
In the case of class W and class O preservatives, use a preservative solution that has a mass  concentration 
such as to ensure that the appropriate requirements for average net retention and  minimum preservative 
penetration  given in table 3 are met. However, in no case may the mass  concentration of type WCCA 
solutions be less than 20 g/L and, where an average net retention for  type WCCA solutions of at least 16 .0 
kg/m3 is required, use a solution that has a mass  concentratio n of at least 40 g/L, except in the case of hazard 
class H6, where a mass concentration  of at least 60 g/L might have to be used . 
 
 NOTE 1  At low levels of mass concentration, high retentions can be difficult to achieve.  
 
NOTE 2  At no time should the tempe rature of a type WCCA solution or the temperature of timber immediately  before 
treatment with such a solution exceed 40 °C.  
 
7.3 Toxicity and safety  
All timber preservatives are pesticides and should therefore be handled, mixed and used with care,  the 
manu facturer's instructions being followed where relevant. (See also clause 9.) Avoid bodily  contact and 
ingestion and take appropriate precautions when mixing or using preservatives.   
7.4 Flammability  
Volatile solvents used in class O preservatives are flamm able. Care is therefore necessary when  class O 
preservatives are in storage and when th ey are used in confined spaces.  Exercise care to exclude water (e.g. 
rain) when a class C preservative is being used in the open  tank process, since the mixing of water with such 
a preservative can, because of frothing and  spilling over, result in a fire hazard . 
 
 DUS 2021 :2019 
© UNBS 2018  – All rights reserved  11 
 8 Application methods for preservatives  
8.1 Surface application  
 
8.1.1 Surface brushing and spraying  
Surface brushing and spraying methods are useful when the t imber has to be treated in situ , and  good results 
can be obtained on the sapwood of softwood timbers when a class O preservative in a  solvent that has good 
penetrating properties is used. Brushing and spraying by hand are less  effective than other applicat ion 
methods because coverage might be incomplete or absorbent areas  of the timber (such as sapwood) might 
not be given the chance to absorb as much as they would if  immersed . 
 
8.1.2 Immersion, steeping, deluging  
8.1.2.1 General  
The penetration and retentio n achieved by immersion, steeping and deluging are much less than  those 
obtained by the treatment processes prescribed in 8.2, and may only be used in the case of  class O 
preservatives used on softwood timber . 
 
8.1.2.2 Immersion  
Immersion is potentially a better method than surface brushing or spraying because it ensures that  all 
surfaces of the timber are covered and are able to absorb the preservative. With short periods of  
immersion (of a few minutes' duration only), low absorption and penetration are ob tained . 
 
8.1.2.3 Steeping  
Steeping is a somewhat better treatment than immersion. Steeping is immersion for longer periods  (hours or 
even days), but this is usually not practical . 
 
8.1.2.4 Deluging  
Deluging is a form of immersion in which individual pieces  of timber are passed through a machine  where they 
are spray ed with preservative for a few seconds. Often the timber is passed through an  enclosed tunnel in 
which the timber is heavily deluged with preservative from a ring of jets although  it is not actual ly immersed . 
 
8.2 Prescribed timber -preservative treatment processes  
8.2.1 General  
To be classified as a timber -preservative treatment, one of the preservative treatment processes shall  be 
used, and the required equipment, as given in 8.3 for each process,  shall be available at the treatment plant . 
 
8.2.2 Diffusion  
The diffusion process is used to treat unseasoned timber. The timber is pressure impregnated with,  sprayed 
with or immersed in a solution of class W, type WB preservative. In the case of non-pressure application 
methods, i.e. immersion or spraying, care should be taken to ensure that all  timber surfaces are adequately 
wetted. After having been wetted, the timber is closed -stacked  under cover for several weeks, to allow the 
preservative to diffuse through the timber. During this  period, the timber has to be kept covered to prevent any 
appreciable drying, since drying will retard  diffusion . 
 
The rate of diffusion depends on the moisture content of the timber, and becomes slower as the  moisture 
conten t is reduced. Diffusion is the result of the slow movement of the preservative  molecules through the  
12 © UNBS 2019 – All rights reserved  
 water in the timber; hence only preservatives that are soluble in water, and  remain so for several weeks while 
in contact with the timber, are suitable for  application by this  method. The only preservatives recommended 
for this application are of type WB. Elevated  temperatures will speed up the process . 
 
 In the case of pressure impregnation, it is important to obtain the required retention during the  treatm ent 
process. The mass concentration of the preservative solution should be adjusted in  accordance with the 
absorption obtained in timber of varying moisture content. Further penetration  of the preservative can be 
achieved by stacking the freshly treated ti mber under cover for a period  of time. The same diffusion principles 
apply as described above.  
 
 
8.2.3 Gas phase process  
The gas phase process involves enclosing timber in a treatment vessel and drawing a vacuum. A  volatile 
preservative, organic borate (tr imethyl borate) (the only preservative recommended for this  process is type 
OB), is then injected into the treatment vessel. The liquid vaporizes under vacuum.  The resulting gas 
penetrates the timber and reacts with timber moisture to form boric acid, whic h is equivalent to the active 
ingredient of type WB timber preservatives. A final vacuum is drawn at the  end of the reaction, to withdraw 
any surplus gas. The treated timber is clean, dry and ready for  immediate use . 
 
8.2.4 Hot or cold open tank process  
The hot or cold open tank process will give effective protection to permeable timbers and to  sapwood, but is 
not recommended for timbers resistant to penetration, for which a high -pressure  process (see 8.2.5) is 
recommended. Only class C preservatives are co mmonly applied by the hot  or cold open tank process. The 
timber is submerged in a tank of preservative which is heated for a  few hours. Then either the preservative is 
allowed to cool while the timber is still submerged or the  timber is transferred to a se parate tank of cold 
preservative. The heating and cooling periods will  vary with the dimensions and species of timber, the type of 
preservative and the efficiency of the  heating and cooling systems . 
 
8.2.5 High -pressure processes  
 
8.2.5.1 General  
Treatment  under pressure is the most effective way of applying a preservative to timber but in the  case of 
some resistant timbers, a high pressure can cause collapse, especially when creosote at a  high temperature 
is used. When such timbers are treated with a class  C preservative, it is advisable  to use a high temperature 
and a moderate pressure. The basic process consists of enclosing the  timber in a treatment vessel (usually a 
cylinder) and forcing the preservative into the timber under  hydraulic pressure. This pr essure is maintained 
until the  required absorption is attained   
 
The pressure may be preceded by a period under vacuum (as in the Bethell (full -cell) process) or  under air 
pressure (as in the Rueping (empty -cell) process). When no preliminary vacuum or  pressure is applied, the 
process is known as the Lowry (empty -cell) process.  After the pressure cycle, the vessel is drained; a vacuum 
is then sometimes applied to adjust the  preservative absorption and to "dry" the surface of the treated timber.   
 
The term " empty -cell" is used because surplus preservative is removed by the expansion of air  compressed in 
the cell spaces while sufficient preservative is left in or on the cell walls to give  adequate protection. The term 
"full-cell" is used because the cell space s are also filled or partially  filled with preservative  
 
 Bleeding of class C preservatives is less likely to occur after an empty -cell process than after a full  cell 
process. Empty -cell processes allow the achievement of deep penetration and the required net retention. DUS 2021 :2019 
© UNBS 2018  – All rights reserved  13 
 Furthermore, when an empty -cell process is used, there is usually less variation in net  retention in individual 
pieces of timber in a charge.  
 
Pressure processes in general can force preservatives deep into timber and achieve high  retentions . They are 
widely used to apply class C and type WCCA and WCuAz preservatives to  timber, and can also be employed 
with type WB preservatives . 
 
8.2.5.2 Bethell (full -cell) process  
Charge the treatment vessel with timber, seal the treatment vessel, apply a v acuum and maintain  the vacuum 
for an adequate period. Without increasing the pressure, introduce the preservative at  an appropriate 
temperature to achieve the requirements given in table 3. Allow the cylinder to fill to  capacity, apply a 
hydraulic pressure  and maintain this pressure until the required absorption is  attained. Release the 
pressure. Pump the surplus preservative from the treatment vessel and,  optionally, apply a final vacuum and 
maintain this vacuum for an appropriate period in order to "dry"  the surface of the timber . 
 
8.2.5.3 Rueping (empty -cell) process  
Charge the treatment vessel with timber, seal the treatment vessel, pump air into the cylinder until a  suitable 
pressure is attained, and maintain this pressure for an adequate period. Then p ump the  preservative, at its 
required temperature, into the treatment vessel at the same pressure. During this  period, the preservative 
displaces the air into an equalizing (Rueping) tank, except that in the  absence of such a tank, the air is 
allowed to es cape from the treatment vessel at such a rate that  the pressure in the treatment vessel remains 
constant .  
 
When the treatment vessel has been filled with preservative, raise the pressure by forcing in  additional 
preservative, and maintain this pressure un til the gross absorption is sufficient to comply  with the 
requirements given in table 3.  When the required gross absorption has been reached, release the pressure 
and drain the  preservative from the treatment vessel. During this period, the compressed air in the timber  
expands and drives out some of the preservative. Finally, apply a vacuum and maintain it until the  surplus 
preservative has been removed from the timber.  The amount of preservative remaining in the timber at the 
end of the treatment is the ne t retention  (see table 3), as distinct from the gross absorption, which is the 
amount contained in the timber at  the end of the pressure period . 
 
8.2.5.4 Lowry (empty -cell) process  
This process is similar to the Rueping process, except that preservative is  pumped into the  treatment vessel 
without any raising of the air pressure in the vessel. Compression of the natural air  in the cell spaces in the 
timber by the preservative helps to expel the excess preservative on  release of pressure .  
 
8.2.6 Low -pressure  process  
The low -pressure process is carried out at ambient temperature, usually by the Lowry process, with  the use of 
pressure but without the application of an initial or a final vacuum.  Charge the treatment vessel with timber, 
seal the treatment vessel,  fill it with preservative and then  introduce additional preservative until the required 
pressure is reached. Maintain this pressure until  the desired absorption is attained. Release the pressure and 
drain the preservative from the  treatment vessel.  Becaus e a final vacuum is not usually applied in this 
process, surfaces of items treated by the low  pressure  process are normally not "dry" immediately after 
treatment . 
 
 This process is only suitable for the application of class O preservatives to finished prod ucts such  as floor 
blocks, flooring strips, door and window frames and other products of normal structural  sizes, and then only 
provided that the required net retention and penetration (see table 3) are  attained. The advantage of this 
process is that it ca n be carried out with the use of light equipment .  
14 © UNBS 2019 – All rights reserved  
  
8.2.7 The vacuum impregnation (double vacuum) process  
The vacuum impregnation process consists of enclosing timber in a treatment vessel and subjecting  it to a 
vacuum. The treatment vessel is flooded with preservative while still under reduced pressure  and, when air is 
admitted, the increased pressure (either atmospheric or slightly above  atmospheric) forces the preservative 
into the timber.  
 
After an appropriate period, the treatment  vessel is drained. A final vacuum is commonly used to enable the 
preservative absorption to be  adjusted and to impart a "dry" surface to the treated timber. The penetration is 
somewhat less than  that achieved by the high -pressure processes.  This process is normally only used f or the 
application of class O preservatives to softwood.  
 
8.3 Equipment required  
At least the minimum required equipment, as given in columns 2 to 8 of table 2, for each timber  preservative  
treatment process, shall be available at the treatment plant . 
 
Table 2 — Minimum equipment required  
1 2 3 4 5 6 7 8 
Permissible treatment processes  
Equipment  Diffusion  Hot or  
cold open  
tank High-pressure processes  Low 
pressure  
process  Double  
vacuum  
process  DUS 2015   DUS 2017   DUS 1722  
Data recorder on  
treatment vessel   
–  
–  
x  
x  
x  
–  
– 
Thermometer a in 
treatment vessel   
X  
X  
X  
X  
X  
X  
X 
Vacuum gauge b on 
vacuum chest or line  – – X X X X X 
Pressure gauge on  
treatment vessel  – – X X X X – 
Retention 
determination  
Method  c X X X X X X X 
Electric moisture  
meterd (DUS 2016 ) X X X X X X X 
Air oven ( 2014  – DUS 1722   
–  
– X  
–  
– 
Increment borer   
X  
X  
X  
X  
X  
X  
X 
Reagent and relevant  
apparatus   
X  
X  
X  
X  
X  
X  
X 
Diameter tape   DUS 1722   
X  
X  
X  
X  
X 
Strength tester   DUS 1722  –  –  X –  X 
NOTE A dash  (–) means “not applicable”.  
a Of capacity 0 °C to 100 °C with a 1 °C accuracy. Thermometers are not required when cold preservatives  are used.  
b The pressure vessel and vacuum chest shall have separate pressure and vacuum gauges, and they shall  have a mi nimum 
diameter size of 100 mm with at least a resolution of 20 kPa. The pressure gauge on the  pressure vessel shall be a 
compound pressure vacuum gauge.  
c Use one of the retention methods as given in DUS 2013, DUS 2018 or ,DUS 2019 . 
d Electric resistance t ype only.  DUS 2021 :2019 
© UNBS 2018  – All rights reserved  15 
 e As required for relevant preservative type.  
 
9 Handling and safety of preservative -treated timber   
To prevent damage to treated timber, pointed tools should only be used on the ends of treated  piles, poles 
and sleepers.  
Timber treated with a class W preservative becomes wet during treatment and, to prevent distortion,  care 
should be taken when the timber is stacked for re -drying. As the mass of the timber is  substantially increased 
by treatment, freshly treated timber should be handled careful ly to avoid  breakages. Preferably do not apply 
metal fittings (excluding anti -split plates and metal markers) to  timber treated with type WCCA and WCuAz 
preservatives, until the period of fixation (see 9.3) is  complete and preferably not until the timber i s dry.  
 
In the case of timber treated with WCuAz, the fixation is less temperature dependent than for  WCCA. After 
impregnation with WCuAz preservative, the freshly treated timber should be protected  from rainfall and direct 
sunlight until the surface is d ry, especially for high retention end uses, and  before dispatch. This usually takes 
48 h.  
 
 In the case of creosoted timber, prevent excessive migration of preservative by using the timber as  soon as 
possible after treatment, subject to its attaining the e quilibrium moisture content of the area  in which it is used. 
It is recommended that creosoted timber that has to be stored for long periods  be rotated (axially) through 
180° once every six months, or be protected from direct sunlight, or  both. 
9.2 Safety  
When handling timber after treatment, wear protective gloves if the timber is still wet or contains  solvent. No 
special precautions are necessary in handling treated timber once the timber has dried,  but carry out the 
normal practice of washing hands before  handling food and before smoking. As  timber treated with creosote 
does not dry out in the same way as timber treated with waterborne or  volatile -solvent -borne preservatives, 
continue taking precautions if the surface of the timber remains  oily.  
 
Restrict  machining of treated timber to a minimum, since machining removes some of the treated  layer. 
However, if it is necessary to machine or to sand timber that has been treated, use an  efficient dust extraction 
system . 
 
9.3 Fixation of WCCA preservatives  
Due t o the toxicity of hexavalent chromium, freshly treated timber should not be dispatched before  fixation of 
WCCA preservative has been reached. The fixation of WCCA preservatives is very  dependent on time versus 
temperature (see annex B), and freshly treated  timber should be stacked  for a period of time until the fixation 
is complete before dispatch.  Fixation is assumed to be complete when the conversion from chromium VI to 
chromium III is  achieved.   
9.4 Disposal  
When treated timber is disposed of it shall b e done as specified in the relevant material safety data  sheets 
(MSDSs)2) of the preservative chemical used to treat the timber.  
9.5 Flammability  
After the solvent has evaporated, timber treated with a class O preservative is no more flammable  than 
untreat ed timber. Provided that the surface of timber has no free creosote (as after a few  months' drying or  
16 © UNBS 2019 – All rights reserved  
 weathering), creosoted timber presents no greater fire hazard than ordinary  timber. Timber treated with a type 
WCCA preservative is subject to afterglow . 
9.6 Safety handling information labelling  
It is recommended that each piece of preservative -treated timber (e.g. poles), or in the case of a  package of 
units or a bundle of pieces (e.g. laths, brandering and battens), each package or bundle,  should have a label 
attached to the piece, package or bundle bearing the following minimum safety  handling information:   
 
a) caution never to burn treated timber;   
 
b) instruction to wear overalls, a dust mask, goggles and gloves when working with treated timber;   
 
c) to dispose of any treated timber waste to a suitable waste disposal site or landfill; and  
 
 d) a reference to where a complete safety information sheet for handling and using preservative  treated  
timber can be viewed or obtained.   
 
The safety handling infor mation may also be printed on the documentation accompanying every lot,  batch, 
package, bundle or piece of preservative -treated timber (e.g. sales invoice).  
 
10 Penetration and net retention  
The appropriate minimum penetrations and net retentions that have  to be obtained to ensure  satisfactory 
service of timber exposed to specific conditions (see clause 5) are given in table  3. 
Table 3 — Requirements for preservative -treated timber  
1 2 3 4 5 6 7 8 
Hazard  
class  Exposure  
class  Timber application  End use  Preservativ
e 
type Average net  
Retention  
(assay  
zone) a 
mass fraction  Average net  
Retention  
 
kg/m3  Minimum 
preservative  
penetration  
(assay zone)  
mm 
Soft 
wood  Hardw
ood Soft 
wood c Hardw
oodd Soft 
wood  Har
dwo
od 
H6 Marine  Timber constantly 
or 
periodically in  
contact with  
estuarine or sea  
water, and subject 
to 
marine borer 
attack  Poles : pilinge; retaining 
walls;  
slipways; groynes; 
jetties; walkways  WCCA  
plus 
Creosote  – 
 
_ – 
 
_ 24 
plus 
200 24 
plus 
200 50 50 
Sawn timber f: pilingg; 
retaining  
walls; slipways; g roynes; 
jetties;  
walkways  WCCA  
plus 
Creosote  – 
 
_ – 
 
_ 24 
plus 
200 24 
plus 
200 Compl
ete 
sapwo
odh Co
mpl
ete 
sap
woo
d 
   Poles : agricultural poles; 
poles  
under flood irrigation; 
bridges;  
pilinge; groynes; 
walkways;  
slipways; jetties; WCCA  
plus 
Creosote  – 
 
0.76 
 
_ – 
 
0.83 
 
_ 16 
or 
4 
or 
130 16 
or 
5,4 
or 
130 25 20 DUS 2021 :2019 
© UNBS 2018  – All rights reserved  17 
 agricultural poles  
for li vestock 
pens/retaining wallse  
H5 Fresh water  Timber constantly 
or 
periodically in  
contact with fresh  
water or heavy 
wet 
soils Sawn  
timber f Pilingg; 
slipways;  
groynes; 
jetties;  
walkways; 
retaining  
walls; culverts; 
flood  
gates; drains  WCCA  
or 
WCuAz  
or 
Creosote  – 
 
0.76 
 
_ – 
 
 
 
_ 16 
or 
4 
or 
130 16 
or 
– 
or 
130 Compl
ete 
sapwo
odh Co
mpl
ete 
sap
woo
d 
Industrial 
cooling  
towersi   
WCCA  
  
– 
  
– 
 30  30 Compl
ete 
sapwo
od Co
mpl
ete 
sap
woo
d 
H4 Ground  
contact  Timber in direct  
contact with the  
ground  Poles  Distribution  WCCA  
or 
WCuAz  
or 
Creosote  – 
 
0.76 
 
_ – 
 
0.83 
 
_ 16 
or 
4 
or 
115 16 
or 
5,4 
or 
115 30 15 
Telephone 
and street  
light WCCA  
or 
WCuAz  
or 
Creosote  – 
 
0.76 
 
_ – 
 
0.83 
 
_ 16 
or 
4 
or 
115 16 
or 
5,4 
or 
115 25  15 
  
18 © UNBS 2019 – All rights reserved  
  
1 2 3 4 5 6 7 8 
Hazard  
class  Exposure  
class  Timber 
application  End use  Preservative  
type Average net  
Retention  
(assay  
zone) a 
mass fraction  Average net  
Retention  
 
kg/m3  Minimum preservative  
penetration  
(assay zone)  
mm 
 
H4 
(continued     Agricultural 
poles;  
landscaping 
structures;  
playground 
structures;  
building; 
fencing;  
pergolas; 
carports;  
flower boxes; 
vine and  
orchard 
trellises  WCCA  
or 
WCuAz  
or 
Creosote  Soft 
wood  Hard  
wood  Soft 
wood c Hard 
wood c 20 13 
– 
 
0,42 
 
– – 
 
0,5 
 
– 12 
or 
2,5 
or 
100 12 
or 
3,3 
or 
100 
 
 Complete  
sapwood  Complete  
sapwood  
Posts (guard -
rail) 
    Piling; 
agricultural  
poles for 
livestock  
pens   
See hazard class 
H5    
 
   Sawn  
timber f 
(and 
specified  
roundwood  
products)  Sawn 
rectangular  
posts; 
landscaping  
structures; 
playground  
structures; 
building;  
fencing; 
pergolas;  
carports; flower 
boxes;  
decking; 
bridges  WCCA  
or 
WCuAz  
or 
Creosote  – 
 
0,42 
 
–  
– 
 
– 
 
– 
 
 
 12 
or 
2,5 
or 
100 12 
or 
2,5 
or 
100 Complete  
sapwood h 
 
 
 Complete  
sapwood  
 
 
 
Complete  
sapwood h 
or 20  Complete  
sapwood  
or 13  
Rail bearers  
20 13 
General 
purpose poles  
    Stakes;  
garden  
edging  
 
 
 Sawn  
 
 
 WCCA  
or 
WCuAz  
or 
Creosote  – 
 
0,42 
 
–  
 
 
 
 – 
 
– 
 
– 6 
or 
2,5 
or 
80 Complete  
sapwood  
 
 
 
 Complete  
sapwood  
 
 
 
 DUS 2021 :2019 
© UNBS 2018  – All rights reserved  19 
  
  
20 © UNBS 2019 – All rights reserved  
  
1 2 3 4 5 6 7 8 
Hazard  
class  
 Exposur
e 
class  Timber 
application  End use  Preservativ
e 
type Average net  
Retention  
(assay  
zone) a 
mass fraction  Average net  
Retention  
 
kg/m3  Minimum 
preservative  
penetration  
(assay zone)  
mm 
Soft 
wood  Hardw
ood Soft 
wood c Hardw
oodd Soft 
wood  Hard
woo
d 
H4 
(continued     Round  
 WCCA  
or 
WCuAz  
or 
Creosote  
 
 
 – 
 
0,42 
 
– – 
 
0,50 
 
– 6 
or 
2,5 
or 
80 6 
or 
3,3 
or 
80 5 5 
 Piling                                       See hazard class H5  
H3 Exterior  
above  
ground  Timber not 
in contact  
with the 
ground but  
exposed 
to 
leaching  
and 
weatherin
g Poles  Cross -arms and 
spacers  WCCA  
or 
WCuAz  
or 
Creosote  – 
 
0,42 
 
– – 
 
0,50 
 
– 6 
or 
2,5 
or 
80 6 
or 
3,3 
or 
80 20 15 
  Landscaping 
structures; 
playground  
structures; 
buildin g; 
fencing rails; 
pergolas;  
carports; vine 
trellis  WCCA  
or 
WCuAz  
or 
Creosote  – 
 
0,23 
 
– – 
 
0,23 
 
– 8 
or 
1,4 
or 
80 8 
or 
1,5 
or 
80 20 13 
Round droppers  10 10 
 Spacer blocks j WCCA  
or 
WCuAz  
or 
Creosote  – 
 
0,23 
 
– – 
 
– 
 
– 8 
or 
1,4 
or 
80 8 
or 
– 
or 
80 Comp
lete 
sapw
ood Com
plete  
sap
woo
d 
        
   Sawn  
timber k 
(and 
specified  
roundwo
od 
products)  Balustrades; 
fencing bearers  
and slats; outdoor 
decking  
and beams; 
garden furniture;  
laminated beams; 
weather  
board; steps; 
cladding; stairs;  
gates; fasci a 
boards; plywood;  
sawn droppers l; 
slabbed  
poles; cylindrical 
rails; halfrounds m WCCA  
or 
WCuAz  
or 
Creosote  – 
 
0,23 
 
– – 
 
– 
 
– 8 
or 
1,4 
or 
80 8 
or 
– 
or 
80 Compl
ete 
sapwo
od Com
plete  
sapw
ood 
 DUS 2021 :2019 
© UNBS 2018  – All rights reserved  21 
  
1 2 3 4 5 6 7 8 
Hazard  
class  
 Exposur
e 
class  Timber 
application  End use  Preservativ
e 
type Average net  
Retention  
(assay  
zone) a 
mass fraction  Average net  
Retention  
 
kg/m3  Minimum 
preservative  
penetration  
(assay zone)  
mm 
Soft 
wood  Hardw
ood Soft 
wood c Hardw
oodd Soft 
wood  Hard
woo
d 
H3 
(conclude
d) internal  Timber 
used 
under a  
roof, not in 
contact  
with the 
ground, 
and 
that will 
not be  
exposed 
to 
leaching  
and 
weatherin
g  General purpose 
poles;  
machined poles n 
for log  
homes  WCCA  
or 
WCuAz  
or 
Creosote  
 
 
 – 
 
0,42 
 
– – 
 
0,50 
 
– 6 
or 
2,5 
or 
80 6 
or 
3,3 
or 
80 5 5 
Laths  
Poles : 
Building 
structure
s; roof  
trusses                                        WCCA  
or 
WCuAz  
or 
Creosote  
or 
TBTOL  
or 
TBTNP  
or 
Borate  
(boric acid  
equivalent
) – 
 
0,23 
 
– 
 
– 
 
– 
 
– – 
 
0,23 
 
– 
 
– 
 
– 
 
– or 
1,2 
or 
80 
or 
1 
or 
1,3 
or 
5 8 
or 
1,5 
or 
80 
or 
1 
or 
1,3 
or   
Sawn 
timber k: 
(and 
specified  
roundwo
od 
products)   Laminated  
beams; roof  
trusses; 
structural  
timber; ceiling  
boards; 
flooring;  
panelling; 
doors;  
cupboards;  
skirting; 
window  
frames; 
plywood;  
slabbed poles;  
cylindrical 
rails;  
half-rounds m WCC A 
or 
WCuAz  
or 
Creosote  
or 
TBTOL  
or 
TBTNP  
or 
ZP 
or 
Borate  
(boric acid  
equivalent
) – 
0,23 
– 
– 
– 
– 
– – 
– 
– 
– 
– 
– 
– 6 
or 
1,4 
or 
80 
or 
1 
or 
1,3 
or 
0,40 
or 
5 6 
or 
– 
or 
80 
or 
1 
or 
1,3 
or 
0,40 
or 
5 Comp
lete 
sapw
ood Com
plete  
sap
woo
d 
 
  
22 © UNBS 2019 – All rights reserved  
     
1 2 3 4 5 6 7 8 
Hazard  
class  
 Exposur
e 
class  Timber 
application  End use  Preservativ
e 
type Average net  
Retention  
(assay  
zone) a 
mass fraction  Average net  
Retention  
 
kg/m3  Minimum 
preservative  
penetration  
(assay zone)  
mm 
Soft 
wood  Hardw
ood Soft 
wood c Hardw
oodd Soft 
wood  Hard
woo
d 
H2 
(conclude
d    General purpose  
poles; machined  
poles n for log  
homes  WCCA  
or 
WCuAz  
or 
Creosote  
or 
TBTOL  
or 
TBTNP  
or 
ZP 
or 
Borate  
(boric acid  
equivalent
) 
 – 
0,23 
– 
– 
– 
– 
– – 
– 
– 
– 
– 
– 
– 6 
or 
1,2 
or 
80 
or 
1 
or 
1,3 
or 
0,40 
or 
5 6 
or 
– 
or 
80 
or 
1 
or 
1,3 
or 
0,40 
or 
5 20 13 
Laths  Deltameth
ri 
  
 
 
-  
  
 
 
-   
 
 
0,003   
 
 
0,003  5 5 
H0-io Dry 
interior  Timber 
used 
under a  
roof, not in 
contact 
with 
the 
ground, 
exposed 
to 
insects 
other than  
termites, 
and not  
exposed 
to fungal  
attack or 
leaching 
and 
weatherin
g Sawn timber k: Mouldings;  
ceilings; floorboards; joinery  Comp
lete 
sapw
ood Com
plete  
sap
woo
d  
 
 
 
 
 DUS 2021 :2019 
© UNBS 2018  – All rights reserved  23 
  
   
1 2 3 4 5 6 7 8 
Hazar
d 
class  
 Exposur
e 
class  Timber application  End use  Preservativ
e 
type Average net  
Retention  
(assay  
zone) a 
mass fraction  Average net  
Retention  
 
kg/m3  Minimum 
preservative  
penetration  
(assay zone)  
mm 
Soft 
wood  Hardw
ood Soft 
wood c Hardw
oodd Soft 
wood  Hard
woo
d 
H0-ito Dry 
interior  Timber used under a 
roof, not in  
contact with the 
ground, exposed  
to insects in cluding 
termites, and  
not exposed to fungal 
attack or  
leaching and 
weathering  Sawn timber k: 
Mouldings;  
ceilings; 
floorboards; joi  Deltameth
ri -  -  0,01  0,01  Comp
lete 
sapw
ood Com
plete  
sap
woo
d 
 
NOTE 1 A dash ( –) means “not applicable”.  
NOTE 2 Timber treated with TBTOL, TBTNP, ZP or borate could be used for hazard class H3, provided that it is continuously 
protected by a suitable well  maintained  
coating  
 
a Average net retention (assay zone) levels expressed in a mass fraction of Cu + biocide.  
b Timber treated  with WCuAz preservatives: If the actual timber density and/or sapwood content are less than those in c) and d), then 
a suitable sampling plan  
(see annex C) may be used to determine the actual net retention, using the following formula: ANR = mass fraction  (column 6) × oven 
dry timber density ×  
sapwood content.  
c In the case of softwoods treated with WCuAz preservatives, the average net retention expressed in kg/m 3 (total volume) is calculated 
by converting from  
the mass fraction active ingredients using an  oven dry timber density of 580 kg/m 3, and a sapwood content of 100 % for sawn timber 
and 90 % for poles.  
d In the case of hardwoods treated with WCuAz preservatives, the average net retention expressed in kg/m 3 (total volume) is 
calculated by converting f rom 
the mass fraction active ingredients using an oven dry timber density of 800 kg/m 3, and a sapwood content of 80 % for large poles, 
and an oven dry density of  
650 kg/m 3, and a sapwood content of 100 % for laths and small diameter poles.  
e Due to preserv ative treatment requirements, all piling and agricultural poles for use in livestock pens or retaining walls that are to be 
used in direct contact with  
the ground or that will be constantly or periodically in contact with fresh water or heavy wet soils (or  both), shall be treated and marked 
in accordance with  
hazard class H5. All piling that will be in contact with estuarine or sea water shall be treated and marked in accordance wit h hazard 
class H6.  
f The only hardwood recommended is species with a permeab le heartwood. Sawn eucalyptus species are not suitable for hazard 
classes H6, H5 and H4.  
g Preferably in round  wood form with complete envelope of sapwood, but if sawn timber is used, a large amount of sapwood shall be 
present.  
h If the required retention is to be achieved, a large amount of sapwood shall be present.  
i Timber selected for 100 % sapwood.  
j Spacer blocks: Full penetration even with lower retention.  
k In the case of hardwood species, some sawn timber products (see 12.3) need not be preservativ e treated due to their low 
penetrability.  
l Type WCCA preservatives shall not be used for the treatment of hardwood sawn droppers.  
m The treatment of half -rounds manufactured from hardwood species with a class W preservative is not recommended.  
n Machined poles for log homes manufactured from hardwood shall be machined in such a way that the sapwood required for 
penetration is not disturbed.  
o The end uses for this hazard class, unlike the other hazard classes, are restricted to those given in column 4 only  (see clauses 5(f) 
and 5(g)). Only products  
included in column 4 shall be allowed to be treated.   
24 © UNBS 2019 – All rights reserved  
 11 Recommendations  for the use of timber preservatives in specific applications  
11.1 Contact with food  
11.1.1 Direct contact with food for human consumption  
For applications in which the preservative -treated timber will be in direct contact with food intended  for human 
consumption, use only a timber preservative of type WB, type WCuAz or type WCCA.   
 
In the case of a type WCCA preservative, do not use the tim ber within 7 d ays of treatment and  thoroughly 
hose the timber down and scrub it or dress it lightly before putting it into use. Such  treated timber is known to 
have been used satisfactorily in cold storage chambers, bread bakery  tunnels, grain storage silo s and fishing 
boats .  
 
NOTE Direct contact is also considered to exist where water can cause a bridging contact between the  preservative -
treated timber and the food.  
 
11.1.2 Direct contact with feeds for livestock  
For applications in which preservative -treated timber will be in direct contact with feeds for livestock  and 
provided that, when the timber is to be used with liquid feeds, the pH value of the feeds is  within the range 6,0 
to 8,0, use only a timber preservative of type WCCA or type WCuAz.  
 
11.1.3 Indirect contact with food or feeds  
 
For applications in which preservative -treated timber will be in indirect contact with food or feeds,  use only a 
timber preservative of type WB, type WCuAz or type WCCA. Class C preservatives may  be used, provided 
that the treated timber is properly coated with an acceptable creosote -compatible  sealant . 
 
 NOTE 1  Indirect contact is considered to exist in the case of truck or container floors, wooden pallets, etc.,  used with 
packed goods.  
11.2 Human contact  
For applicatio ns in which preservative -treated timber is in direct contact with the human skin, for  example in 
the case of playground equipment, use only a timber preservative of type WB or  type WCuAz. Class C 
preservatives and a type WCCA preservative may be used, prov ided that the  treated timber is properly coated 
with an acceptable sealant which, in the case of class C  preservatives, is creosote -compatible. Timber 
preservatives could be hazardous to people with  sensitive skins . 
 
11.3 Animal contact  
11.3.1 Continuous d irect contact  
For applications in which preservative -treated timber will be in continuous direct contact with  animals (and 
bees), use only the following preservatives : 
 
a) for animals : all preservatives other than class C, and preservatives other than clas s O that  contain 
pentachlorophenol or its salts; and  
 DUS 2021 :2019 
© UNBS 2018  – All rights reserved  25 
 b) for bees : type WCuAz and suitable preservatives of type WB which should be painted or  protected by a 
suitable water repellent.  
 
NOTE  In the case of an organic solvent -borne preservative, the solvent should be allowed to evaporate  completely before 
the timber is used.  
 
11.3.2 Periodic direct contact  
For applications in which preservative -treated timber will be in periodic contact with animals, all  classes of 
preservatives may be used. Where repeated li cking of treated timber by animals can be  expected, use a type 
WCCA or a type WCuAz preservative. In the case of a creosote -based  preservative, use a type and a process 
of application such as to minimize bleeding.   
  
11.4 Contact with plants  
There are no r estrictions on the class of preservative to be used on timber that will be in direct  contact with 
plants, although damage could appear on plants as a result of direct contact with  freshly creosoted timber . 
  
11.5 Combustion gases  
Because toxic gases will b e released as a result of the combustion of preservative -treated timber,  take care to 
avoid prolonged exposure to such gases . 
 
11.6 Timber for use in cooling towers  
The use of softwood, treated as in (a) to (d) below, is recommended for cooling towers:  
a) preservative : use a type WCCA preservative;  
b) solution strength : use a solution strength of at least 60 g/L;  
c) retention : see table 3; and  
d) penetration : see table 3.  
 
12 The use of preservative -treated timber in specific areas in Uganda . 
 
12.1 Qualific ation  
To qualify as being adequate for its purpose, structural timber of the two main species used in a  permanent 
building in the areas given in 12.2 and 12.3 shall be preservative treated in accordance  with 12.4  
 
12.2 Gymnospermae (coniferous species)  
Sawn timber (including planed and profiled timber) and poles or logs (round or partly round) of the  softwood 
species shall be treated in accordance with 12.4 when used in the following municipal    
 
12.3 Angiospermae (broadleaved species  
All sawn timber, plane d timber, and poles or logs (round or partly round) of the hardwood species  shall be 
treated in accordance with 12.4 when used within the borders of  Uganda , except for  the following items:  
a) laminated timber;  
b) block and strip flooring;   
26 © UNBS 2019 – All rights reserved  
 c) ceiling bo ards;  
d) paneling ;  
e) mouldings and joinery;  
f) garden furniture;  
g) outdoor decking boards; and  
h) non -sapwood -containing, kiln -dried and planed, sawn boards processed from eucalyptus  species).  
12.4 Preservative treatment  
The preservative treatment o f timber shall comply with the provisions of us EAS 3226, US EAS 3264, USEAS 
3225    
13 Treatment plant area compliance   
All treated timber shall be treated in a preservative treatment plant that complies with the provisions  given in 
annex D. The checklist  given in annex E shall be used for conformity assessment.    
 
 
 
Annex A  
(informative)  
Permeability of commercial timber species  
A.1 Amenable to impregnation  
The sapwood of the following timbers can be easily impregnated, the heartwood only sometimes.  
 
SOFT WOODS         HARDWOODS . 
Pinus canariensis       Eucalyptus fastigata  
P. caribaea         E. fraxinoides  
P. elliottii          E. grandis  
P. patula  
P. pinaster  
P. roxburghii  
P. taeda  
 
A.2 Moderately amenable to impregnation  
The sapwood of the following timbe rs can be fairly easily impregnated, the heartwood rarely.  
SOFTWOOD        HARDWOODS  
Pinus radiata        Entandrophragma cylindricum (Sapele)  
Eucalyptus citriodora  
E. cladocalyx  
E. cloeziana  
E. diversicolor  
E. maculata  
 
 
 
 
 
 
 DUS 2021 :2019 
© UNBS 2018  – All rights reserved  27 
 Annex B  
(Informative ) 
WCCA fi xation chart  
The fixation chart in figure B.1 gives an indication of the time versus  timber temperature required for 
fixation  to be achieved.  
 
   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
28 © UNBS 2019 – All rights reserved  
 Annex C  
(Informative )  
Sapwood and density calculation for the determination  of WC uAz timber -preservative 
retentions  
C.1 Introduction  
This standard includes the option for timber treatment plants to determine preservative retentions  
(expressed as kilograms per cubic metre) using a mass fraction retention, the oven dry density of  
the tre ated or assay zone, and the sapwood content of the material being processed.   
 
This sampling method should be used to determine the target retention (kilograms per cubic metre)  
of the total timber volume by determining the basic actual oven dry density and  sapwood content of  
the timber being treated at a given timber treatment plant.  
 
C.2 Materials needed  
 
C.2.1 Determination of basic sapwood content  
To determine basic sapwood ratio, 30 or more pieces of timber from the same population as the lot  
to be trea ted is selected at random. If the samples are sawn timber, then no more than 3 pieces  
may be selected from the same package of units or bundle of pieces (e.g. brandering, battens and  
flooring, and decking boards). The sample can be kept in the stacks or in  their bundles, and merely  
marked for observation.  
 
C.2.2 Determination of basic density  
To determine basic density, 30 or more pieces of timber from the same population as the lot to be  
treated are selected at random. The maximum moisture content of the s amples shall be as required  
in the relevant product specification. The pieces are to consist of 100 % sapwood and be at least  
300 mm in length with a minimum mass of 100 g.  
 
C.3 Method  
 
C.3.1 Apparatus  
 
C.3.1.1 Calibrated digital scale , capable of measurin g to the nearest 1,0 g.  
 
C.3.1.2 Electric moisture meter , preferably fitted with insulated electrodes and suitable for the  
determination of moisture content of timber.  
 
C.3.2 Determination of the basic density ( DB) 
 
C.3.2.1 In order to determine the basic density of the timber, the oven dry density ( DOD) of each  
timber sample in kilograms per cubic metre is determined by using the following formula:  
 
D =      M X 0.001  
OD                MC 
         1+   1000         x V 
where  
M is the mass of the sample , in grams;  
MC is the average moisture content of the three measurements per sample, in grams per  DUS 2021 :2019 
© UNBS 2018  – All rights reserved  29 
 kilogram;  
V is the calculated volume of the sample, in cubic metres.  
 
C.3.2.2 The basic density ( DB) is determined by using the following formula:  
DB = DAVE + SD 
where  
DB is the basic density, in kilograms per cubic metre;  
DAVE is the average oven dry density of all the samples (as determined in C.3.2.1), in  
kilograms per cubic metre;  
SD is the standard deviation of all the samples, in kilograms per cubic metre . 
 
C.3.3 Determination of the basic sapwood content ( SC) 
 
C.3.3.1 In order to determine the basic sapwood content, the sapwood content of each timber  
sample is determined by observing the one end of each sample. Before making any observations,  
carry out th e following procedure:  
a) spray the one end of the untreated sample with a heartwood indicator pertinent to the timber  
species;  
b) measure the average diameter of the sample at the sprayed end ( OD); and  
c) measure the average diameter of the heartwood port ion (HD). 
C.3.3.2 Determine the sapwood content of the sample ( SCs) as a percentage, as follows:  
 
SCs= OD2 – HD2 X 100  
OD2 
where  
OD is the average overall diameter of the sample, in millimeters ; 
HD is the average heartwood diameter of the sample, in millimeters . 
 
C.3.3.3 Calculate the basic sapwood content ( SC) as a percentage, as follows:  
SC = SAVE + SDP  
 
where  
SAVE is the average sapwood ratio of all the samples (as determined in C.3.3.2), as a  
percentage;  
SDP is the standard deviation of all the sample s, as a percentage.  
 
C.3.4 Determination of the target average net retention (total timber volume)  
Calculate the minimum retention ( R) in kilograms per cubic metre, as follows:  
R  DBX SCX ANR  
  10 000  
where  
R is the average net retention, in kilograms of  active chemical per cubic metre total volume;  
DB is the basic density (as determined in C.3.2.2 above), in kilograms per cubic metre;  
SC is the basic sapwood content (as determined in C.3.3.3 above), as a percentage;   
30 © UNBS 2019 – All rights reserved  
 ANR is the average net retention as gi ven in column 6 of table 3, as a mass fraction.  
NOTE The sampling method should be repeated:  
a) at least every three months; or  
b) when a new timber supplier is used; or  
c) when a different timber species is used to the timber previously sampled  
or any com bination of (a), (b)  
and (c)).  
(normative)  
 DUS 2021 :2019 
© UNBS 2018  – All rights reserved  31 
 Annex D  
(Normative ) 
Treatment plant area conformity requirements  
 
D.1 Occupational hygiene  
 
D.1.1 Emergency facilities  
Emergency showers and eyewash facilities shall be installed within the bunded area.  
 
D.1.2 C ontaminated water from showers and eyewash facilities  
Water from the showers or eyewash facilities that is contaminated with treating solution shall not be  
discharged into the ablution drains or storm water drains. In the case of waterborne preservatives,  
the contaminated water could be used in the preparation of treating solutions; otherwise it shall be  
collected and stored until it can be neutralized and disposed of in an approved way (see  D 3) 
 
D.1.3 Eating, drinking and smoking  
No eating, drinking or sm oking shall be allowed within the treatment area (see D.2.2.10.1) and no  
foodstuffs shall be stored within this area.  
 
D.1.4 Rainwater  
Provision shall be made to divert all storm water from the treatment area. This diverted water shall  
remain uncontaminate d. Should there be any signs of contamination, the water shall be contained  
and used in the treatment process. (See also D.1.2.)  
 
D.2 Safety  
 
D.2.1 Chemical safety programme  
Chemical safety is an important part of an environmental management programme. Sig nificant  
elements shall include:  
a) monitoring programmes for workers’ health, in order to ensure that exposure limits are adhered  
to and that proper records are kept of accidents and incidents involving chemicals  
b) appointing a person responsible for mon itoring occupational health and safety;  
c) using only registered chemicals and keeping all relevant information on handling, storage and  
first aid up to date;  
d) controls to ensure that correct handling and safety procedures are followed by all employees;  
e) information on and training in the above, involving employees (see D.5.1); and  
f) ongoing liaison with local emergency services (fire brigade, hospitals, etc.) regarding chemical  
safety procedures.  
 
D.2.2 Plant safety  
 
D.2.2.1 Bunded area  
 
D.2.2.1.1 Gen eral 
All constituent parts of a timber treatment plant shall be within a bunded area. The bunded area  may 
be either covered or uncovered (see D.2.2.10.3). The walls and floor of the pit or bunded area  shall 
be of an impervious material and shall be maintai ned in that condition.   
32 © UNBS 2019 – All rights reserved  
  
NOTE ideally  all bund walls should finish above normal ground level.  
 
D.2.2.1.2 Size  
The pit or bunded area shall be of adequate size to accommodate the total volume of the chemicals  
present, plus 10 % of the volume. A separate bund ed tank farm of adequate size to accommodate  
the volume as determined in table D.1 shall be provided for chemicals in storage. (See D.2.4.)  
Table D.1 — Total volume of tank farm  
1 2 
Number of tanks  Total volume of tank farm  
1 110 % of the volume of the t ank 
2 100 % of the volume of the largest tank plus 50 % of the volume of the  second 
tank plus 10 % of this calculated volume of the two tanks.  
 
3 100 % of the volume of the largest tank plus 30 % of the volume of the  remaining 
two tanks plus 10 % of this  calculated volume of the three  tanks  
 
4 100 % of the volume of the largest tank plus 20 % of the volume of the  remaining 
three tanks plus 10 % of this calculated volume of the four  tanks.  
 
5 100 % of the volume of the largest tank plus 15 % of the volum e of the  remaining 
four tanks plus 10 % of this calculated volume of the five  tanks.  
 
6 100 % of the volume of the largest tank plus 12 % of the volume of the  remaining 
five tanks plus 10 % of this calculated volume of the six tanks.  
 
7 or more  100 % of the volume of the largest tank plus 10 % of the volume of the  remaining 
six or more tanks plus 10 % of this calculated volume of the  seven or more tanks.  
 
 
 
D.2.2.1.3 Position  
The location of the door of the treatment vessel relative to the pit or to the bund wall shall be such  
that any chemical solution remaining in the treatment vessel spills into the pit (or bunded area).  
 
D.2.2.2 Treatment vessels  
 
D.2.2.2.1 General  
If compressed air or liquid pressure is used during the treatment process, the treatmen t vessel shall  
comply with the requirements of the relevant national legislation (see foreword)  All treatment 
vessels shall be regularly inspected for deterioration, for example corrosion, and  immediately 
repaired when necessary.  
 
D.2.2.2.2 Seal  
Before the  door of a treatment vessel is closed, care shall be taken to ensure that the door seal is in  
position and has been wiped clean of any debris, and that the seal is in good workable condition.  
 
D.2.2.2.3 Door safety  
The door of the treatment vessel shall be  closed during non -working hours. A warning notice  
indicating that all the chemical solution in the treatment vessel has been pumped out shall be  placed 
on the door face, even though a reliable mechanical fail -safe interlock system is installed  (see DUS 2021 :2019 
© UNBS 2018  – All rights reserved  33 
 D.2.2. 2.4). Where the door is suspended from a single bolt, a safety chain shall be added in  case 
the bolt breaks.  
 
NOTE  A treatment vessel door that is not fully and safely locked during the treatment process can be  dislodged and blown 
open either by internal p ressure or by the weight of the solution . 
 
D.2.2.2.4 Fail -safe interlock system  
Except in the case of multiple -bolt doors, a fail -safe interlock system (mechanical, not  electrical) that  
will prevent the door of the treatment vessel from being opened during  the process cycle shall be  
fitted to avoid unnecessary spillage and flooding.  
 
NOTE  An example of such a fail -safe interlock system is a valve fitted over the door -opening mechanism,  which will 
prevent the operator from loosening the bolt direct, in order  to open the door. This valve will have to  be opened first and all 
remaining internal pressure will therefore be relieved . 
 
D.2.2.2.5 Control panel signal  
In the case of automated plants, the control panel shall receive an electrical signal indicating when  
the door is fully locked.  
 
D.2.2.2.6 Pressure -relief valves  
The treatment vessel shall be provided with a pressure -relief valve that prevents the plant from  
being operated at pressures exceeding the working pressure of the treatment vessel. An additional  
pressure -relief valve shall be provided if the pressure pump is capable of exceeding the test  
pressure of the vessel. It shall be set to bypass at a slightly higher pressure (+25 kPa to +50 kPa)  
than the first pressure -relief valve, thus acting as an added  safety  precaution. The valve shall be  sealed 
to prevent tampering or unnecessary adjustment.  
 
D.2.2.2.7 Vacuum chest  
If a vacuum chest is linked into the vacuum line, a quick -action valve shall be situated between the  
treatment vessel and the vacuum chest  and shall be kept in the closed position during any pressure  
cycle. The chest shall be fitted with a sight glass or with a level switch.  
NOTE When the treatment vessel is full, the solution level will show in the sight glass and the 
operator can  close the  valve to stop the vacuum pump from flooding. A level switch will stop the 
vacuum pump when the  treatment vessel is flooded.  
 
D.2.2.2.8 Marking  
Each treatment vessel defined by the relevant national legislation (see foreword) as a pressure  
vessel shall be legibly and durably marked with at least the following information:  
a) the design code;  
b) the working pressure and test pressure;  
c) the treatment vessel manufacturer's name;  
d) the drawing number;  
e) the date of manufacture;  
f) the date of the hydraulic pressure test, and the test pressure, in megapascals;  
g) the inspection authority (where applicable); and  
h) the plant manufacturer's unique identification number.  
 
D.2.2.2.9 Rails  
The rails shall be clear and in good working condition. When the treatment vessel is loaded, the  rails 
shall be aligned and properly secured to prevent derailments. Provision shall also be made to  
prevent the trolleys from floating off the rails during the treatment process.    
34 © UNBS 2019 – All rights reserved  
 D.2.2.3 Tanks  
 
D.2.2.3.1 General  
All tanks manufacture d from corrosive materials shall be protected against external corrosion (by  
means of at least a prime coating and a top coating). Where corrosive chemicals are used, the  
interior of the tanks shall be coated with a suitable epoxy coating.  
 
D.2.2.3.2 Posit ion 
The tanks shall be placed on a firm foundation within the bunded area. If mild steel tanks are used,  
they shall be elevated above the ground for air circulation by 50 mm to 100 mm.  
 
D.2.2.3.3 Vapours  
Some chemicals or solvents give off flammable vapour s. Smoking shall not be allowed in the  
treatment plant areas. "No smoking" signs shall be posted. Because vapours can accumulate in a  
closed tank or above a creosote tank or under a roof, tanks shall be well vented. Special  
precautions shall be taken when tanks are being cleaned, when samples are being drawn from a  
creosote tank or when a manhole or door is being opened. The correct safety clothing shall be worn  
at all times (see D.5.2.7). Smoking areas shall be demarcated.  
 
D.2.2.3.4 Maintenance and inspec tion 
All closed -up tanks shall be fitted with manholes for maintenance and inspection purposes. Manhole  
covers shall be secure. The manholes shall be so positioned that they are accessible and, if  
possible, well ventilated. No individual shall be allowed t o enter an enclosed tank without having  
obtained the necessary authorization by management and without supervision.  
 
D.2.2.3.5 Open tanks  
Open tanks shall be protected with suitable handrails to prevent persons from falling into them.  
D.2.2.3.6 Sampling ta ps 
All above -ground working tanks (excluding creosote tanks) shall have easily accessible sampling  
taps that give a representative sample of the contents. Each sampling tap shall be locked or shall  
have a removable handle.  
 
D.2.2.3.7 Marking  
Each tank shal l be legibly and durably marked with at least the following information:  
a) the total tank capacity, in litres;  
b) the construction material;  
c) the wall thickness, in millimeters ; 
d) the type of treatment solution that the tank contains; and  
e) in additio n, in the case of measuring and mixing tanks, the tank capacity, in litres per millimeter  of 
depth.  
 
D.2.2.4 Pipe work and valves  
 
D.2.2.4.1 Pipe work  
All pipe work shall be protected against damage and corrosion, and shall be easily accessible for  
inspect ion and maintenance.  
 
D.2.2.4.2 Valves  
Valves shall be easily accessible for operation and regular inspection. All valves shall be closely  
checked for leakages, especially on the vacuum circuit, where air leakage is more difficult to detect.  
 
D.2.2.4.3 Tan k overflow  DUS 2021 :2019 
© UNBS 2018  – All rights reserved  35 
 Tanks shall be provided with overflow pipes of suitable diameter to ensure fast drip -free overflow  
from storage tanks to measuring tanks and from measuring tanks to mixing tanks. These overflow  
pipes shall form part of a closed -circuit system.  
 
D.2.2.5 Water supply  
To prevent siphoning or back -flow, a water supply pipe shall feed into the top of a tank that forms  
part of the treatment plant unless fitted with a ball float valve. (See also D.1.2.)  
 
D.2.2.6 Mixer (if present) and mixing process  
 
D.2.2.6.1 Design  
The design of a mixer shall be such as to prevent any liquid from being splashed or spilled from the  
mixing tank.  
D.2.2.6.2 Mixing process  
 
D.2.2.6.2.1 The mixing process shall take place at atmospheric pressure. During the loading of  
chemic als into the mixing tank, the procedures recommended by the chemical supplier shall be  
followed.  
 
D.2.2.6.2.2 Treatment solutions shall be introduced from the mixing tank into the storage tanks by  
means of a closed -circuit system.  
 
D.2.2.6.2.3 Chemical con centrates in liquid or paste form shall be passed carefully into a dosing  vat, 
from where they will be gradually introduced into the mixing tank.  
 
D.2.2.6.2.4 Chemicals in powder form shall be carefully placed into a perforated cage within the  
mixing tank.  From there, they will then be flushed into the solvent in the mixing tank, to provide the  
working solution required.  
 
D.2.2.6.2.5 The mixing process should preferably be done by agitation and not by stirring. If the  
agitators create rotation of the conten ts, side baffle fins shall be installed in the mixing tank.   
 
NOTE Mixing by means of a high volume transfer pump is very efficient.  
 
D.2.2.6.3 Open container  
Open chemical containers shall not be stored in the mixing area. The chemicals needed for a mix  
shall be used up or shall be returned to the lock -up storage area. All empty containers and  
containers with unused chemicals shall also be returned to the lock -up storage area (see  also 
D.2.4). Mixes shall be calculated in full drum or bag multiples, since it is undesirable to have  small 
portions of the concentrated chemicals lying about.  
 
D.2.2.6.4 Drum washers  
A drum washer should be used to empty containers of paste products. High -pressure water jets  
should be avoided as a means of mixing, owing to the he alth hazard presented by the mist.  
 
D.2.2.7 Pumps  
 
D.2.2.7.1 Protective guard  
All couplings, pumps and motor shafts shall be well protected, to prevent loose clothing from getting  
caught in them.  
D.2.2.7.2 Leakage  
Pumps shall be regularly inspected for lea ks. Gland leakage shall be led away to the sump or pit,  for 
recovery into the treatment system.  
  
36 © UNBS 2019 – All rights reserved  
 D.2.2.8 Electrical control panel  
 
D.2.2.8.1 Protection  
All electrical control panels and switches shall be situated under cover, away from rain, chemical  
spray  and spillage.  
 
D.2.2.8.2 Labelling  
All valves, switches, isolators, etc., shall be suitably identified to enable a person to operate the  
plant after he has read the treatment manual. All functions of the plant shall be recorded step by  
step in the manual,  with all the valve numbers being given.  
 
D.2.2.8.3 Electrical installation  
All electrical installations shall be installed by a qualified competent person and shall be checked at  
regular intervals to ensure that the equipment is in safe working order.  
 
D.2.2.8.4 Flameproof equipment  
In terms of SANS 60079 -1, flameproof motors and fittings shall be used in the case of flammable  
solutions (including creosote and light organic solvent preservative (LOSP)) and shall be checked  
and maintained and the results ke pt on record.  
 
D.2.2.9 Haulage or extraction of timber from the treatment vessel  
Timber handling equipment varies and is generally dependent on local conditions. A forklift or winch  
is often used. To prevent injuries and downtime, equipment (e.g. winch dru m, rope and lifting  
devices) shall be regularly inspected and checked. The winch shall be protected with an overload  
switch and a drum guard to prevent cross -winding: in the case of bollard winches, a foot -switch that  
will allow the operator to stop the wi nch, and in the case of drum winches, a non -latching dead  
man's switch.  When applicable, crosby clamps shall be fitted correctly.  
 
D.2.2.10 Site  
 
D.2.2.10.1 Treatment and storage areas  
The areas for the treatment of timber and for the storage of treated ti mber shall be clearly  
demarcated. All practical precautions shall be taken to prevent the environment from becoming  
contaminated with timber treatment chemicals.  
 
D.2.2.10.2 Drip pads  
 
D.2.2.10.2.1 Storage drip pad  
If a treatment process without a final va cuum is used, a storage drip pad shall be provided that is  
adjacent to the treatment plant and that can accommodate a quantity of timber at least 10 % more  
than the maximum quantity treated over any 24 h period. The storage drip pad shall have an  
imperviou s floor slab that drains back to the pit or bunded area, to contain any drippage or spillage.  
(See also D.4.1.)  
 
D.2.2.10.2.2 Bogie rail drip pad  
A bogie drip pad, immediately adjacent to the treatment plant and of at least the same length as the  
treatment  vessel, shall be provided at bogie rails and traverses. The drip pad shall have an  
impervious floor slab that drains back with a minimum fall of 1:500 to the bunded area, to contain  
any drippage or spillage. The drip pad shall project at least 300 mm on e ither side of the timber  
bogies on the rails or traverses.  
 
D.2.2.10.3 Cover  DUS 2021 :2019 
© UNBS 2018  – All rights reserved  37 
 At least one of the following requirements shall be met:  a) If the size of the bunded area conforms 
only to D.2.2.1.2, then a cover is required over at least  the bunded area plus over any other drip 
pads that drain into the bunded area.  
b) A cover over the bunded area is not required if the bunded area complies with the requirements  
of D.2.2.1.2 and can accommodate a 1 in 50 year flood over an area that includes the bunded  area 
and any uncovered drip pads that drain into the bunded area.  
 
D.2.2.10.4 Housekeeping  
Housekeeping is of the utmost importance in and around the treatment plant area. All areas that are  
subject to the build -up of chemical deposits (except oil -borne preservati ves and LOSPs) shall be  
kept clean by regular hosing down with water, which shall be directed into collection sumps for 
reuse  or for suitable disposal. The practice of dry sweeping is not allowed.  Oil-borne preservatives 
and LOSP deposits shall be soaked u p with sawdust and shall be disposed  of in accordance with 
D.3. 
D.2.2.10.5 Stacking  
Timber shall be stacked safely and neatly to prevent it from falling and causing injuries. The height  
of a stack shall be not more than three times its base width.  
 
D.2.3 O perator’s office or control room  
 
D.2.3.1 General  
There shall be a functional operator’s office or control room at the plant.  
 
D.2.3.2 Ergonomics  
 
D.2.3.2.1 Lighting  
To ensure a pleasant working atmosphere, the operator's office should be large enough and have  
adequate lighting. It should be able to accommodate a suitable sink, shelves for equipment, and a  
desk, chair and filing cabinet or cupboard.  
 
D.2.3.2.2 Ventilation  
The operator's office shall be well ventilated to remove all vapours.  
 
D.2.3.3 Office rules  
Only the authorized personnel shall be allowed into the office. Only laboratory chemicals and tools  
used in the treatment process may be kept in the office, neatly stored. Chemical analysis may be  
done in the office but, after analysis, all the sampl es shall be returned to the treatment plant.  
 
D.2.4 Chemical off -loading and storage area  
 
D.2.4.1 Off -loading area  
All deliveries of chemicals shall be made in a clearly demarcated lockable storage area. This area  
shall be of sufficient size to accommodat e bulk or drum supplies (or both). Care shall be taken to  
provide adequate safety during the off -loading and storing procedures.  Protective clothing shall be 
worn while the chemicals are being handled. (See also D.5.2.)  The off -loading area shall be paved 
with impervious load -bearing material and shall be so designed  that it drains into the bunded area 
appropriate for the type of chemical being stored.  
 
D.2.4.2 Locked storage area  
Chemicals shall only enter the treatment plant in adequately sealed container s or in tankers. The  
chemicals shall be kept in a lock -up storage area or tank. A stock book of all chemicals received  
and mixed shall be kept in accordance with the Quality Management Systems procedures.  
 
  
38 © UNBS 2019 – All rights reserved  
 D.3 Waste management and disposal  
 
D.3.1 Contamin ated materials  
 
D.3.1.1 Treated timber  
 
D.3.1.1.1 Disposal of treated timber waste  
Treated timber waste shall be disposed of in a suitable and lawful way. Disposal options for timber  
waste treated with currently used chemicals are given in D.3.1.1.2 and D. 3.1.1.3. Treated timber  
shall not be used for domestic heating, or for cooking or for making charcoal.  
 
D.3.1.1.2 Timber treated with copper -chromium -arsenic (CCA)  
Timber treated with CCA shall be disposed of in an approved landfill. Timber treated with CC A shall  
not be disposed of by means of burning.  
 
D.3.1.1.3 Timber treated with other treatment chemicals  
Timber treated with other treatment chemicals shall be disposed of in an approved landfill or by  
burning. Burning shall only be carried out in non -residential areas, and the ash shall be disposed of  
in an approved landfill.  
 
D.3.1.2 Containers and packaging  
All used containers (drums, plastics bags, etc.) shall be neutralized and rinsed three times and  
returned to the chemical supplier. If this is not po ssible, containers shall be neutralized and made  
unusable by holing and crushing before disposal in a dumping area approved by the local  
authorities. (Rinsing should be re -used as process water.)  
 
NOTE Contaminated waste (drums, containers, plastics bags, etc.) that accumulates on the site 
should not  be disposed of in municipal dumping areas.  
 
D.3.1.3 Other contaminated material  
Contaminated sawdust, sand, etc., shall be disposed of in a dumping area approved for the purpose  
by the relevant regulatory autho rity. These waste materials shall not be used for mulching,  
gardening or any commercial purposes.  
 
D.3.2 Chemical sludge  
Sludge shall be stored in containers that are resistant to acid corrosion as recommended by  
registered waste disposal companies. These containers shall be stored in a secure bunded area  
and shall be disposed of by a registered waste disposal company. Chemical sludge shall not be  
disposed of into sewers or municipal drains.  
 
NOTE Chemical sludge is produced by a chemical reaction in the tr eatment solution. Sludging can 
be caused  by temperature, acidity changes, wood extractives, iron contamination and minerals in 
the water. It covers all  the solid paste and other suspensions that accumulate in, among other 
places, pressure cylinder door sum ps, open tanks (hot or cold open tank process) and flooding pits 
and at the bottom of working tanks.  
 
D.3.3 Spillages  
All spillages shall be reported to management, in accordance with the relevant national legislation  
(see foreword). (See also D.7.4.) Mino r contained spills can be  
 
a) brushed or directed into the pit or sump and pumped into the appropriate storage tanks, or  
 
b) soaked up with an absorbent material such as sand, placed in suitable containers and disposed  
of as toxic waste by a registered wa ste management company.  DUS 2021 :2019 
© UNBS 2018  – All rights reserved  39 
  
 
D.4 Post -treatment handling  
 
D.4.1 Freshly treated timber  
All freshly treated timber shall be drip free before dispatch. In the case of timber treated with CCA,  
the timber should be stacked for a period of time which will allow fo r sufficient fixation of the CCA  
chemical before it is dispatched to the purchaser or end user. Excess chemical solution shall be  
kept for re -use in the treatment process or for safe disposal (see D.2.2.10.2, D.3.2 and D.3.3).  
 
D.4.2 Manual removal from tr eatment vessel  
Special care shall be taken to avoid direct contact of the chemicals with the body when timber is  
being extracted by hand. Gloves and protective clothing shall be worn (see D.5.2).   
 
D.4.3 Cleaning the storage and bogie rail drip pads  
To pre vent dust from waterborne preservatives accumulating on a concrete drip pad area, the drip  
pad areas shall be hosed down at least once a week and the washings shall be collected for re -use 
(see D.2.2.10.2.2).  
 
D.5 Health risks  
 
D.5.1 Training  
 
D.5.1.1 Plant operators and workers shall be instructed and trained in the correct handling and use  
of the treatment chemicals. Training shall be carried out by qualified competent person(s) and shall  
include emergency procedures in the case of a personal accident or an exposure to spillage. The  
quality control manager and the safety officer shall also be trained.  
 
D.5.1.2 All training shall be provided for by management on an ongoing basis as required by the  
relevant national legislation (see foreword). Records shall be kept of all training done by the  
employees.  
 
D.5.2 Personal protective equipment  
D.5.2.1 General  
Personnel shall remove their protective clothing when they leave the treatment area and shall put it  
on again before they re -enter. Provision shall be made  for protective clothing for visitors to the  
treatment area. The basic protective clothing and accessories that shall be provided, and the  
applicable standards, are listed in table D.2.  
 
D.5.2.2 Head and eye protection  
Personnel who open drums, mix chemica ls or open the treatment vessel door shall wear hard hats  
with face visor or goggles, in order to protect the head and face and especially the eyes.  
Table D.2 — Basic protective clothing and accessories  
1 2 
Item  Description  
 
Hard hat  Made of ABS plasti cs with polyethylene suspension, adjustable hat  
Face visor or goggles  Made of clear polymethylmethacrylate, with plated metal harness to fit  
Respirator  Covers nose and mouth with replaceable filter pad.  
Barrier cream  Forms a very efficient barrier to th e action of preservative chemicals on  
the skin. Seek advice on the correct cream to use for each  
preservative. (This information is available from the preservative  
supplier.)  
Gloves  Fabric reinforced PVC. Excellent chemical resistance and physical  
protect ion 
Safety suit or overall  Special design in woven polypropylene gives the operator good   
40 © UNBS 2019 – All rights reserved  
 protection from dust or splashes of preservative and is itself unaffected  
by chemicals. The overall shall be washed after 2 d to 3 d usage.  
Apron  PVC or rubber type to be worn over the overal  
Footwear  PVC gum boots  
 
D.5.2.3 Nose and mouth protection  
A nose and mouth respirator shall be worn when powder or crystalline preservatives are being  
opened and mixed. The respirator filter pad shall be changed regularly or di sposable face masks  
shall be worn. When the door of a treatment vessel is being opened, a respirator and face mask  
shall be worn to prevent inhalation of the fumes. Respirators and face masks shall be capable of  
controlling the exposure to below the occupa tional exposure limit (OEL) for the relevant hazardous  
chemical substance (HCS).  
 
D.5.2.4 Hand, arm and face protection  
A water -resistant and chemical -resistant barrier cream   shall be  available. When handling treated 
timber, mixing treatment chemicals, o pening chemical drums or  operating the treatment plant, 
personnel shall wear strong PVC -coated gloves. Contaminated  gloves shall not be worn outside the 
treatment area.  It is recommended that persons with skins sensitive to the treatment chemical used 
shou ld not be  allowed to work in the treatment area.  
 
D.5.2.5 Body protection  
When duties are being carried out within the treatment area, a PVC apron shall be worn over the  
overall in order to protect the body. The recommended overall has no pockets and is ac id resistant;  
it should be laundered frequently on site. The laundry water may be added to other contaminated  
water (see D.1.2).  
 
D.5.2.6 Foot protection  
PVC gum boots fitted with safety toecaps provide the best foot protection. Alternatively, safety  
shoes  could be recommended for warm climates, but not on sites that are likely to be muddy and  
wet. 
 
D.5.2.7 Maintenance of protective equipment  
All protective clothing and equipment shall be inspected on a regular basis to ensure that they are  
kept in good con dition and efficient working order fit for the purpose intended.  
 
D.6 Plant emergency equipment  
The following minimum plant emergency equipment shall be available and easily accessible at all  
timber treatment plants:  
a) spade;  
b) stable broom;  
c) bucket (p referably PVC);  
d) suitable fire -fighting equipment; and  
e) bags of neutralizing chemicals (kept under lock and key), and instructions for use (as supplied by  
the chemical supplier or the manufacturer).  
 
D.7 Accident prevention, safety and first aid  
 
D.7.1  Safety awareness  
Selected posters, banners and slogans relating to safety in the workplace shall be displayed at  
strategic points at the treatment plant. Screening of safety films can effectively promote safety  
awareness.  
 
D.7.2 Labelling of chemicals  
Safety labels, as required by the relevant government department (see foreword), shall be available  
for all the relevant chemicals used.  DUS 2021 :2019 
© UNBS 2018  – All rights reserved  41 
  
D.7.3 First -aid kit  
A complete first -aid kit shall be available at the treatment plant near the treatment area. All  
emer gency medication, for example for burns, chemicals in eyes, chemical inhalation or ingestion,  
shall be available. The first -aid equipment shall never be situated in the same room as the  
chemicals.  
 
D.7.4 Material safety data sheets (MSDSs)  
MSDSs obtained f rom suppliers or manufacturers of the treatment chemicals shall be displayed in  
the operator's office or control room and in other strategic positions. Material safety data sheets  
shall include first -aid treatment and emergency spillage procedures for the preservative chemicals  
used in the treatment plant.  
 
  
42 © UNBS 2019 – All rights reserved  
  
 
Table D.2 — Basic protective clothing and accessories  
 
1 2 
Item  Item Description  
Hard hat  Made of ABS plastics with polyethylene suspension, adjustable hat size.  
Face visor 
or 
goggles  Made of cl ear polymethylmethacrylate, with plated metal harness to fit the helmet.  
Respirator  Covers nose and mouth with replaceable filter pad.  
Barrier 
cream  Forms a very efficient barrier to the action of preservative chemicals on the skin. Seek 
advice on the co rrect cream to use for each preservative. (This information is available 
from the preservative supplier.)  
Gloves  Fabric reinforced PVC. Excellent chemical resistance and physical protection.  
Safety suit 
or 
overall  Special design in woven polypropylene gi ves the operator good protection from dust or 
splashes of preservative and is itself unaffected by chemicals. The overall shall be 
washed after 2 d to 3 d usage.  
Apron  PVC or rubber type to be worn over the overall.  
Footwear  PVC gum boots.  
 DUS 2021 :2019 
© UNBS 2018  – All rights reserved  43 
 Annex E  
(Normative )  
Checklist for conformity assessment of treatment plant area  
The checklist in table E.1 shall be used to indicate requirements strictly to be followed in order to  conform to 
the standard and from which no deviation is permitted.  
 
Table E.1 — Check list for treatment plant area compliance  
 
1 2 3 
Item  Criterion  Remark  
1 Occupational  
hygiene  1) Have emergency showers and eyewash 
facilities been installed within the bunded 
area?   
 
2) Is contaminated water from the showers 
and eyewash facilities co ntained or 
recovered?   
 
3) Is the policy of no eating, drinking or 
smoking applied by means of visible warning 
signs?   
 
4) Is storm water diverted from the treatment 
plant?   
5) Have provisions been made for 
contaminated storm water to be contained?   
2 Safety  
2.1 Chemical  
safety programme  Has a chemical safety programme been 
introduced that includes the following:  
a) A monitoring programme for workers’  
health?  
b) Appointing a person responsible for 
occupational health and safety?  
c) Are only registere d chemicals used and is 
the relevant information on handling storage 
and first aid up to date?  
d) Controls to ensure that correct handling 
and safety procedures are followed by 
employees?  Information on and training in 
the above?  
e) Information on and tra ining in the  
above?  
f) Ongoing liaison with local emergency 
services regarding chemical safety 
procedures?   
2.2 Plant safety  
a) Bunded area  1) Are all the constituent parts of the timber 
treatment plant within the bunded area?  
  
2) Are the floor and wal l impervious?   
3) Can it contain the total contents of the  
plant plus 10 %?  
  
4) If there is a separate bunded tank farm,  
can it accommodate a chemical volume as 
calculated in table D.1? Table D.1   
 5) If there is no roof over the treatment plant, 
can the pit or bunded area contain the total 
contents of the plant plus 10 % plus an 
allowance for a 1 in 50 year flood?   
  
44 © UNBS 2019 – All rights reserved  
 Table E.1 (continued ) 
1 2 3 
Item  Criterion  Remark  
b) Treatment vessel  1) Is the door positioned so as to contain  
any spillage with in the pit (or bunded area)?   
 
2) If the vessel is coded, is it inspected in 
accordance with the requirements of the relevant 
national legislation (see foreword)?   
3) Is the door seal clean and in a good workable 
condition?   
 
4) Is storm water divert ed from the treatment 
plant?   
5) Is there a vessel -door warning sign indicating 
that the vessel is empty when vessel is not in 
operation?   
6) If the door is not a bolted type, does it have a 
mechanical fail -safe system?   
7) Has a pressure -relief valv e been fitted?   
8) Is a second pressure -relief valve required?   
9) If a vacuum chest is linked into the vacuum line, 
is there a valve between  
the vessel and the vacuum chest?   
10) Is the vacuum chest fitted with a sight  
glass or a level switch?   
11) If the vessel is defined as a pressure vessel, 
does it have the required information marked on it?   
12) Are the internal rails aligned and clear?   
4) If the door has a single bolt hanger, does it have 
a safety chain?   
5) If there is no roof over th e treatment plant, can 
the pit or bunded area contain the total contents of 
the plant plus 10 % plus an allowance for a 1 in 50 
year flood?   
13) Is there an anti -float system?   
c) Tanks  1) Are the tanks externally or internally painted? 
(Mild steel tank s only)   
2) Are they mounted on a firm foundation within 
the bunded area or tank farm?   
3) If mild steel tanks are used, are they elevated 
above the ground?   
4) If they contain oil -based or light organic  
solvent preservatives, are they well vented?   
5) If the tanks are closed, do they have inspection 
manholes?  
  
6) If the tanks are open, do they have handrails?  
  
7) Do the above -ground working tanks (excluding 
creosote tanks) have sampling taps?  
  
 DUS 2021 :2019 
© UNBS 2018  – All rights reserved  45 
 Table E.1 (continued ) 
1 2 3 
Item  Criterion  Remark  
c) Tanks  
(concluded  8) Is each tank legibly and durably  
marked with the following information:  
a) Total tank capacity, in litres?  
b) Construction material?  
c) Wall thickness, in millimeters ? ) 
d) The type of treatment solution  
contained in the t ank?  
e) In the case of measuring and  
mixing tanks, the tank capacity, in  
litres per millimeter  of depth?   
9) Do the tanks have a closed -circuit  
overflow system?   
d) Pipe work and  
valves   
1) Are the pipes protected against damage?   
2) Are the pipes pro tected against corrosion?   
3) Are the pipes easily accessible?   
4) Are the valves easily accessible?   
5) Do the valves leak?   
6) Are the valves clearly labelled?   
7) Do the overflow pipes form part of a  
closed -circuit system?   
e) Water supply  If there is no ball float valve, does the water supply 
pipe fill the tank from the top?   
f) Mixer and mixing  
process  1) If present, has the mixer been designed to prevent 
liquid from splashing and spilling from the mixing 
tank?   
2) Is the mixing solution  introduced to the storage 
tanks via a closed -circuit system?   
3) If the chemical is a liquid or paste, is it introduced 
into the mixing tank via a dosing vat?   
4) Does the mixing tank have a perforated cage (for 
powders only)?   
5) Does the mixing ta nk have side baffle fins to 
prevent rotation (if an agitator is used)?   
6) Are drum washers used to empty containers of 
paste products?   
 7) Are there any high -pressure water jets  
that could cause mist, which could  
cause a health hazard?   
g) Pumps  1) Do the pumps (including couplings and  
motor shafts) have protective guards?  
  
2) Is gland leakage led into the sump or  
pit for recovery?   
  
46 © UNBS 2019 – All rights reserved  
 Table E.1 (continued ) 
1 2 3 
Item  Criterion  Result  
h) Electrical control  
panel  1) Is there a locked -door signal  (automated plants only)?   
2) Is the electrical panel under cover?   
3) Are the switches and isolators labelled?   
4) Is the control panel in working order?   
5) Are there flameproof motors (oil -based and light 
organic solvent preservatives only)?   
i) Winches  If the plant has winches, then   
1) Does the winch have overload protection?   
 2) Is there a drum guard?   
3) Does the winch have a foot -switch (bollard winches 
only)?   
4) Is there a non -latching dead man’s switch (drum winch 
only)?   
j) Treatment and D.2.2.10.1  
storage area  
demarcation  1) Is the treatment plant area demarcated?   
2) Is the treated timber storage area demarcated?   
k) Drip pads  If the process has no final vacuum   
1) Is there a storage drip pad?   
2) Can it accommodate ti mber treated over a 24 h period 
plus 10 %?   
3) Is it positioned adjacent to the treatment plant?   
4) Is it constructed from impervious materials?   
5) Does it drain into the pit or bunded area so that excess 
chemical solution can be kept for re -use?   
6) Is there a bogie rail drip pad provided at the bogie rails 
and  
a) Is it at least as long as the vessel?   
b) Is it constructed from impervious materials?   
c) Is it positioned adjacent to the treatment plant?   
d) Does it drain into the pit or b unded area?   
l) Housekeeping  1) Is waterborne deposit build -up in the treatment plant 
area regularly hosed down and collected for re -use or 
suitable disposal?   
2) In the case of oil -borne preservatives and LOSPs, is 
the build -up regularly soaked up with  sawdust and 
disposed of?   
 DUS 2021 :2019 
© UNBS 2018  – All rights reserved  47 
 Table E.1 (continued ) 
1 2 3 
Item  Criterion  Result  
2.3 Operator's  
office or control room  1) Is an operator’s office or control room  
provided?   
2) Does it have adequate lighting?   
3) Is it well ventilated?   
4) Is it a ccessible to authorized personnel  
only?   
5) If the control room is used as a laboratory, are all the 
samples removed and returned to the treatment plant after 
analysis?   
6) Are MSDSs of the chemicals displayed  
in the control room?   
2.4 Chemical off -  
loading and storage  
area 1) Are the chemical off -loading and storage areas clearly 
demarcated?   
2) Is the chemical off -loading and storage area constructed 
from impervious materials?   
3) Can spillages be contained in the  loading and storage 
area?   
4) If not, do they drain into the pit or bunded area?   
5) Is the chemical kept in a lock -up storage area or tank?   
6) Is a stock book kept of all chemicals received?   
3 Waste  
management and  
disposal  
3.1 Storage   
1) Are empty containers stored in the lo ck-up storage area?   
2) Is the chemical sludge stored in appropriate containers?   
3) Are these containers of chemical sludge stored in the pit 
or bunded area?   
3.2 Disposal  1) Is treated timber waste disposed of in an approved 
manner ?   
2) Are all u sed containers neutralized and returned to the 
chemical supplier, or  
disposed of in an approved manner?   
3) Is all contaminated sawdust, sand, etc., disposed of in an 
approved manner?   
4) Is the chemical sludge disposed of in an approved 
manner?   
3.3 Spillages  1) Are spillages reported?   
2) Has provision been made for minor spillages to be 
contained within the bunded area?   
3) Is absorbent material available to soak  
up minor spillages?   
  
48 © UNBS 2019 – All rights reserved  
 Table E.1 (continued ) 
1 2 3 
Item  Criterion  Remark  
4 Pos t-treatment  
Handling  
4.1 Freshly treated  
timber  1) Is all the freshly treated timber drip free  
before dispatch?   
2) Has the timber treated with CCA been  
stacked for a period of time to allow for  
sufficient fixation of the CCA chemical  
before being dispat ched to the  
purchaser or end user?   
4.2 Manual removal D.4.2  
from treatment  
vessel  1) Has special care been taken to avoid  
direct contact of the chemical with the  
body when extracting timber by hand?   
2) Are records kept for the training done  
by each em ployee?   
4.3 Cleaning the  
storage and bogie  
rail drip pads   
1) Are the drip pad areas hosed down at  
least once a week?   
Health risks  
5.1 Training  1) Have the plant operators and workers  
been trained in the correct handling  
and use of treatment chemicals as well  
as the emergency procedures in the  
case of an incident?   
2) Are records kept for the training done  
by each employee?   
5.2 Personal  
protective  
equipment (PPE)  1) Has the appropriate PPE been  
issued to people working with  
preservative chemicals an d freshly  
treated timber and is it used?   
2) Is the appropriate PPE available for  
visitors?   
3) Is the PPE removed before leaving the  
treatment plant area and put back on  
before re -entering?   
 4) Is the PPE maintained and kept in  
good working conditio n, and is it fit for  
its intended purpose?   
6 Plant emergency  
equipment  1) Is the emergency equipment listed in  
D.6 available and in close proximity to  
the treatment plant?   
2) Are the neutralizing chemicals kept  
under lock and key?   
7 Accident  
prevent ion, safety  
and first aid  1) Is safety awareness being promoted by  
means of posters, banners or slogans?   
 2) Are safety labels available for the  
chemicals used?   
 3) Is a complete first -aid kit available at  
the treatment plant (not in the same  
room as t he chemicals)?   
 4) Apart from the control room, are  
MSDSs displayed in strategic  
positions in the treatment plant area?   
 DUS 2021 :2019 
© UNBS 2018  – All rights reserved  49 
 Bibliography  
[1] ISO ##### -#, General title — Part #: Title of part  
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© UNBS 2018  – All rights reserved  51 
 Certification marking  
Products that conform to Uganda standa rds may be marked with Uganda National Bureau of Standards 
(UNBS) Certification Mark shown in the figure below.  
The use of the UNBS Certification Mark is governed by the Standards Act, and the Regulations made 
thereunder. This mark can be used only by tho se licensed under the certification mark scheme operated by 
the Uganda National Bureau of Standards and in conjunction with the relevant Uganda Standard. The 
presence of this mark on a product or in relation to a product is an assurance that the goods comp ly with the 
requirements of that standard under a system of supervision, control and testing in accordance with the 
certification mark scheme of the Uganda National Bureau of Standards. UNBS marked products are 
continually checked by UNBS for conformity to  that standard.  
Further particulars of the terms and conditions of licensing may be obtained from the Director, Uganda 
National Bureau of Standards.  
 
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