

October 1, 1991

Mr. Robert Screws
Project Engineer
Knott Laboratory, Inc.
2727 West 2nd Avenue
Denver, Colorado 80219

Dear Mr. Screws:

This is in response to your July 18, 1991, letter in which you request information concerning the force factor used in the Occupational Safety and Health Administration's (OSHA) regulations for fall arrest systems. We apologize for the delay in responding to your inquiry.

In response to your inquiry, please be advised that OSHA has adopted a 1.4 force factor as the appropriate conversion ratio to be used to convert human force limits to equivalent force limits when rigid test weights are used. This concept is briefly discussed in the preamble to the July 28, 1989, Final Rule for Powered Platforms for Building Maintenance [54 FR 144]. A copy of the relevant preamble is enclosed for your information.

If we may be of further assistance, please don't hesitate to contact Mr. Roy F. Gurnham at (202) 523-8136.


Patricia K. Clark, Director
Directorate of Compliance Programs


July 18, 1991

Attn. Roy Gernum, Office of Construction
and Maritime Compliance Assistance
Room N3610
200 Constitution Ave,. N.W.
Washington, D.C. 20210

Dear Mr. Gernum,

After an extensive review of the Code of Federal Regulations and Federal Register, I have not been able to find a direct reference to the conversion factor for the maximum arrest force registered with a rigid mass to the maximum arrest force registered with the articulated manikin or the human body when testing fall arrest systems.

In "Introduction to Fall Protection" by J. Nigel Ellis, Ph.D., CSP, the author states that OSHA has adopted a 1.4:1 force factor of a steel weight to the human body. I called Dr. Ellis to determine the specific location of his statement in the Federal Register and he pointed out an indirect description in 1910.66 appendix C.

It states that personal fall arrest systems when stopping a fall shall limit the maximum arresting force on an employee to 1,800 pounds (8kN) when used with a body harness. And in the force test, a system fails the force test if the recorded maximum arresting force exceeds 2,520 pounds (11.2kn) when using a body harness. Since the force test requires the use of a rigid weight, the accepted conversion factor can easily be calculated as:

            c = 2520 pounds (11.2kN) = 1.4
                1800 pounds (8kN)

However there is no direct statement that addresses this force conversion factor in the code or preamble.

In my research I have personally called Dr. Ellis, Andrew Sulowski, and Barbara Belaski in your office, and they all agree that OSHA accepts 1.4 for the force conversion factor of steel or rigid weight to a manikin or human body.

Since my situation involves the construction industry, and the proposed safety standard to Walking and Working Surfaces and Personal Protective Equipment (Fall Protection Systems) dated Tuesday, April 10, 1990, is very similar to 1910.66 appendix C I would like to formally request a letter of interpretation from you.

Specifically, I am in need of a statement similar to:

OSHA has adopted a 1.4 force factor of a steel or rigid weight to a manikin or human body with respect to fall arrest systems.

If I can clarify any portion of this letter for you please contact me. I have included all material referred to for your information. I sincerely appreciate the effort your staff has made to accommodate my situation. It has been a pleasure dealing with competent and informative employees in the Washington D.C. OSHA branch.

Very truly yours,


Robert E. Screws
Project Engineer