2.3: Nails, Hammers and Pneumatic Nailers
Nails
Nails of all sizes are commonly used to assemble wood products when glue and adhesives are not of sufficient strength for a project. They are known by number size, the lesser the number, the smaller the length and diameter. The number is followed by the letter “d”. The d is the symbol for penny, which can be traced back as far as the Ancient Roman Empire. There are various theories as to how the measurement term came to be, but what is confirmed is that the d stands for the Roman coin denarius, or in English, the penny. The denarius was the coin which many people used in the Roman empire at the time when Rome occupied what is now England, so that’s why it’s called a penny but uses a “d” as the symbol.
Some styles of nails have larger heads for greater holding power while others have smaller or no head so that it can be set flush with or lower than material surfaces for cosmetic applications. When “headless” finish or casing nails are used, it is best to drive them to just slightly above the surface while being careful not to leave hammer marks on the material’s being nailed surface and then use a “nail set” tool to embed the nail.
| Size |
Length
(inches) |
Diameter
(inches) |
Standard Wire
Guage |
Number Per
Pound |
|---|---|---|---|---|
| 2d | 1 | 0.072 | 15 | 900 |
| 3d | 1.25 | 0.080 | 14 | 615 |
| 4d | 1.5 | 0.090 | 12 | 322 |
| 5d | 1.75 | 0.098 | 12 | 254 |
| 6d | 2 | 0.113 | 11 | 200 |
| 7d | 2.25 | 0.113 | 11 | 154 |
| 8d | 2.5 | 0.131 | 10 | 106 |
| 9d | 2.75 | 0.131 | 10 | 85 |
| 10d | 3 | 0.148 | 9 | 74 |
| 12d | 3.25 | 0.148 | 9 | 57 |
| 16d | 3.5 | 0.162 | 8 | 46 |
| 20d | 4 | 0.192 | 6 | 29 |
| 30d | 4.5 | 0.207 | 5 | 23 |
| 40d | 5 | 0.225 | 4 | 17 |
| 50d | 5.5 | 0.244 | 3 | 14 |
| 60d | 6 | 0.262 | 2 | 11 |
Common Nails for Building & Construction Projects
Query \(\PageIndex{1}\)
Hammers
Hammers are used to strike or cause impact and are available in traditional designs and in a variety of models, sizes, and weights to perform specific tasks. Selecting the proper hammer for a particular task can be the determining factor for being able to complete the task or be the difference between quality and sub-par craftsmanship. The following list describes the most common types of hammers and some of the types of tasks they are often used for.
Query \(\PageIndex{1}\)
General Hammer Use
No matter which type of hammer is used, employing proper techniques will help prevent injury.
- Wear safety glasses when striking any object with any type of hammer or tool.
- For hardwood, before nailing with hammer, drill pilot hole in material to prevent splitting.
- Choose a hammer weight that is comfortable.
- “Set” the nail by tapping in the point, remove the free hand before driving the nail.
- Using the center of the hammer face, drive the nail with smooth, firm blows.
- Striking face should always be parallel with the surface being hit.
- Avoid sideways or glancing blows.
- Always strike with the hammer face.
- Avoid impact with handle or shaft of hammer.
Nail Gun Safety
The following information is compiled from OSHA safety literature. Please go to https://www.osha.gov/Publications/Na..._optimized.pdf if you wish to view the brochure in it’s entirety.
- Department of Health and Human Services: Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health
- Department of Labor: Occupational Safety and Health Administration
This guidance document is not a standard or regulation, and it creates no new legal obligations. It contains recommendations as well as descriptions of mandatory safety and health standards [and other regulatory requirements]. The recommendations are advisory in nature, informational in content, and are intended to assist employers in providing a safe and healthful workplace. The Occupational Safety and Health Act requires employers to comply with safety and health standards and regulations promulgated by OSHA or by a state with an OSHA-approved state plan. In addition, the Act’s General Duty Clause, Section 5(a)(1), requires employers to provide their employees with a workplace free from recognized hazards likely to cause death or serious physical harm.
Nail guns are used every day on many construction jobs—especially in residential construction. Thy boost productivity but also cause tens of thousands of painful injuries each year. Nail gun injuries are common—one study found that 2 out of 5 residential carpenter apprentices experienced a nail gun injury over a four-year period. When they do occur, these injuries are often not reported or given any medical treatment. Research has identified the risk factors that make nail gun injuries more likely to occur. The type of trigger system and the extent of training are important factors. The risk of a nail gun injury is twice as high when using a multi-shot contact trigger as when using a single-shot sequential
trigger nailer.
The guidance is for residential home builders and construction contractors, subcontractors, and supervisors. NIOSH and OSHA developed this publication to give construction employers the information they need to prevent nail gun
injuries. Types of triggers and key terms are described. The guidance highlights what is known about nail gun injuries, including the parts of the body most often injured and the types of severe injuries that have been reported. Common
causes of nail gun injuries are discussed and six practical steps that contractors can take to prevent these injuries are described. These are:
1) Use full sequential trigger nail guns;
2) Provide training;
3) Establish nail gun work procedures;
4) Provide personal protective equipment (PPE);
5) Encourage reporting and discussion of injuries and close calls; and
6) Provide fist aid and medical treatment.
The guidance includes actual workplace cases along with a short section on other types of nail gun hazards and sources of additional information.
Introduction to Nail Gun Safety
How likely are nail gun injuries?
Nail guns are powerful, easy to operate, and boost productivity for nailing tasks. They are also responsible for an estimated 37,000 emergency room visits each year. Severe nail gun injuries have led to construction worker deaths.
Nail gun injuries are common in residential construction. About two-thirds of these injuries occur in framing and sheathing work. Injuries also often occur in roofing and exterior siding and finishing
A study of apprentice carpenters found that:
- 2 out of 5 were injured using a nail gun during their 4 years of training.
- 1 out of 5 were injured twice.
- 1 out of 10 were injured three or more times.
Worksite Story – A 26-year-old Idaho construction worker died following a nail gun accident in April 2007. He was framing a house when he slipped and fell. His finger was on the contact trigger of the nail gun he was using. The nosepiece hit his head as he fell, driving a 3-inch nail into his skull. The nail injured his brain stem, causing his death. The safety controls on the nail gun were found to be intact. Death and serious injury can occur using nail guns—even when they are working properly.
More than half of reported nail gun injuries are to the hand and fingers. One quarter of these hand injuries involve structural damage to tendons, joints, nerves, and bones. After hands, the next most often injured are the leg, knee, thigh, foot, and toes. Less common are injuries to the forearm or wrist, head and neck, and trunk. Serious nail gun injuries to the spinal cord, head, neck, eye, internal organs, and bones have been reported. Injuries have resulted in paralysis, blindness, brain damage, bone fractures, and death.
Nail guns present a number of hazards and risks. NIOSH and OSHA prepared this publication to provide builders and contractors with the latest information on nail gun hazards and practical advice on the steps they should take to prevent nail gun injuries on their construction jobs.
This guide covers nail guns (also called nailers) used for fastening wood, shingles, and siding materials. The guide refers specifically to pneumatic tools but also applies to nail guns that use gas, electric, or hybrid power sources. It does NOT cover powder actuated tools used for fastening material to metal or concrete. The guide assumes that contractors are generally familiar with how nail guns work and the various types of specialized nail guns (for example, framing, roofing, flooring)
This guide is applicable to all nail guns. The emphasis is on framing (“stick” and “coil”) nail guns because they fie the largest nails, are the most powerful, and are considered to be the most dangerous to use.
Know Your Triggers
Nail gun safety starts with understanding the various trigger mechanisms. Here is what you need to know:
How Triggers Differ
All nailers rely on two basic controls: a finger trigger and a contact safety tip located on the nose of the gun. Trigger mechanisms can vary based on: 1) the order in which the controls are activated, and 2) whether the trigger can be held in the squeezed position to discharge multiple nails OR if it must be released and then squeezed again for each individual nail. Combining these variations gives four kinds of triggers. Some nail guns have a selective trigger switch which allows the user to choose among two or more trigger systems. Each trigger type is described below along with a summary of how the controls are activated.
Query \(\PageIndex{1}\)
The bottom line: contractors should check the tool label and manual for manufacturer-specific trigger names and operating information.
Worksite Story – Two framers were working together to lay down and nail a subfloor. One framer was waiting and holding the nail gun with his finger on the contact trigger. The other framer was walking backwards toward him and dragging a sheet of plywood. The framer handling the plywood backed into the tip of the nail gun and was shot in the back. The nail nicked his kidney, but fortunately he recovered. As a result of this incident, the contractor switched to using only sequential triggers on framing nail guns. Co-workers can get injured if they bump into your contact trigger nail gun. You can prevent this by using a full sequential trigger.
How do Nail Gun Injuries Happen?
Useful Terms
- Recoil is the rapid rebound or kickback after the nailer is fired.
- A double fire occurs when a second nail unintentionally fires because the nailer re-contacted the work piece after recoil. It can also occur if the safety contact slips while the user is positioning the nail gun. Several tool manufacturers offer “anti-double fire” features for their nail guns.
There are seven major risk factors that can lead to a nail gun injury. Understanding them will help you to prevent injuries on your jobsites.
1. Unintended nail discharge from double fire. Occurs with CONTACT triggers.
The Consumer Product Safety Commission (CPSC) found that contact trigger nailers are susceptible to double firing, especially when trying to accurately place the nailer against the work piece. They found that a second unintended firing can happen faster than the user is able to react and release the trigger. Unintended nails can cause injuries.
Double fire can be a particular problem for new workers who may push hard on the tool to compensate for recoil. It can also occur when the user is working in an awkward position, such as in tight spaces where the gun doesn’t have enough space to recoil. The recoil of the gun itself can even cause a non-nail injury in tight spaces if the nail gun hits the user’s head or face.
2. Unintended nail discharge from knocking the safety contact with the trigger squeezed. Occurs with CONTACT and SINGLE ACTUATION triggers.
Nail guns with contact and single actuation triggers will fire if the trigger is being held squeezed and the safety contact tip gets knocked or pushed into an object or person by mistake. For example, a framer might knock his leg going down a ladder or bump into a co-worker passing through a doorway. Contact trigger nailers can release multiple nails and single actuation trigger nailers can release a single nail to cause injury.
Holding or carrying contact trigger or single actuation trigger nail guns with the trigger squeezed increases the risk of unintended nail discharge. Construction workers tend to keep a finger on the trigger because it is more natural to hold and carry an 8-pound nail gun using a full, four-finger grip. Tool manufacturers, however, do warn against it.
Common nail gun grip by OSHA is licensed under Public Domain
3. Nail penetration through lumber work piece. Occurs with ALL trigger types.
Nails can pass through a work piece and either hit the worker’s hand or fly of as a projectile (airborne) nail. A blow-out nail is one example. Blow-outs can occur when a nail is placed near a knot in the wood. Knots involve a change in wood grain, which creates both weak spots and hard spots that can make the nail change direction and exit the work piece. Nail penetration is especially a concern for placement work where a piece of lumber needs to be held in place by hand. If the nail misses or breaks through the lumber it can injure the non-dominant hand holding it.
4. Nail ricochet after striking a hard surface or metal feature. Occurs with ALL trigger types.
When a nail hits a hard surface, it has to change direction and it can bounce of the surface, becoming a projectile. Wood knots and metal framing hardware are common causes of ricochets. Problems have also been noted with ricochets when nailing into dense laminated beams. Ricochet nails can strike the worker or a co-worker to cause an injury.
5. Missing the work piece. Occurs with ALL trigger types.
Injuries may occur when the tip of the nail gun does not make full contact with the work piece and the discharged nail becomes airborne. This can occur when nailing near the edge of a work piece, such as a plate. Positioning the safety contact is more difficult in these situations and sometimes the fired nail completely misses the lumber. Injuries have also occurred when a nail shot through plywood or oriented strand board sheeting missed a stud and became airborne.
Nail penetration through the lumber is a special concern where the piece is held in place by hand. Nail gun by OSHA is licensed under Public Domain
6. Awkward position nailing. Occurs with ALL trigger types. Unintended discharges are a concern in awkward position work with CONTACT and SINGLE ACTUATION triggers.
Nailing in awkward positions where the tool and its recoil are more difficult to control may increase the risk of injury. These include toe-nailing, nailing above shoulder height, nailing in tight quarters, holding the nail gun with the non-dominant hand, nailing while on a ladder, or nailing when the user’s body is in the line of fie (nailing towards yourself). Toe-nailing is awkward because the gun cannot be held flush against the work piece. Nailing from a ladder makes it difficult to position the nail gun accurately. Nailing beyond a comfortable reach distance from a ladder, elevated work platform, or leading edge also places the user at risk for a fall.
Toe-nailing by OSHA is licensed under Public Domain
7. Bypassing safety mechanisms. Occurs with ALL trigger types.
Bypassing or disabling certain features of either the trigger or safety contact tip is an important risk of injury. For example, removing the spring from the safety contact tip makes an unintended discharge even more likely. Modifying tools can lead to safety problems for anyone who uses the nail gun. Nail gun manufacturers strongly recommend against bypassing safety features, and voluntary standards prohibit modifications or tampering. OSHA’s Construction standard at 29 CFR 1926.300(a) requires that all hand and power tools and similar equipment, whether furnished by the employer or the employee shall be maintained in a safe condition.
About 1 in 10 nail gun injuries happen to co-workers. This is from either airborne (projectile) nails or bumping into a co-worker while carrying a contact trigger nail gun with the trigger squeezed.
You Should Know –
Studies of residential carpenters found that the overall risk of nail gun injury is twice as high when using contact trigger nail guns compared to using sequential trigger nail guns.
*Note that the studies could not quantify injury risks associated with specific tasks; it is likely that some nailing tasks are more dangerous than others.
A voluntary ANSI standard 10 calls for all large pneumatic framing nailers manufactured after 2003 to be shipped with a sequential trigger. However, these may not always be FULL SEQUENTIAL triggers. Contractors may need to contact manufacturers or suppliers to purchase a FULL SEQUENTIAL trigger kit.
Worksite Story – A carpenter apprentice on his fist day ever using a nail gun injured his right leg. He was working on a step ladder and was in the process of lowering the nail gun to his side when the gun struck his leg and fired a nail into it. He had no training prior to using the nail gun. New worker training is important and should include hands-on skills.
Six Steps to Nail Gun Safety
1. Use the full sequential trigger
The full sequential trigger is always the safest trigger mechanism for the job. It reduces the risk of unintentional nail discharge and double fires—including injuries from bumping into co-workers.
-
At a minimum, provide full sequential trigger nailers for placement work where the lumber needs to be held in place by hand. Examples include building walls and nailing blocking, fastening studs to plates and blocks to studs, and installing trusses.
- Unintended nail discharge is more likely to lead to a hand or arm injury for placement work compared to flat work, where the lumber does not need to be held in place by hand. Examples of flat work include roofing, sheathing, and subflooring.
- Consider restricting inexperienced employees to full sequential trigger nail guns starting out. Some contractors using more than one type of trigger on their jobs color-code the nail guns so that the type of trigger can be readily identified by workers and supervisors.
-
Some contractors have been reluctant to use full sequential triggers fearing a loss of productivity. How do the different types of triggers compare?
- The one available study had 10 experienced framers stick-build two identical small (8 f x 10 ft. wood structures—one using a sequential trigger nail gun and one using a contact trigger nail gun. Small structures were built in this study so that there would be time for each carpenter to complete two sheds.
- Average nailing time using the contact trigger was 10% faster, which accounted for less than 1% of the total building time when cutting and layout was included. However, in this study the trigger type was less important to overall productivity than who was using the tool; this suggests productivity concerns should focus on the skill of the carpenter rather than on the trigger.
- Although the study did not evaluate framing a residence or light commercial building, it shows that productivity is not just about the trigger. The wood structures built for the study did include common types of nailing tasks (flat nailing, through nailing, toe-nailing) and allowed comparisons for both total average nailing time and overall project time. The study did not compare productivity differences for each type of nailing task used to build the sheds.
2. Provide training
Both new and experienced workers can benefit from safety training to learn about the causes of nail gun injuries and specific steps to reduce them. Be sure that training is provided in a manner that employees can understand. Here is a list of topics for training:
- How nail guns work and how triggers differ.
- Main causes of injuries – especially differences among types of triggers.
- Instructions provided in manufacturer tool manuals and where the manual is kept.
Hands-on training with the actual nailers to be used on the job. This gives each employee an opportunity to handle the nailer and to get feedback on topics such as:
- How to load the nail gun
- How to operate the air compressor
- How to fie the nail gun
- How to hold lumber during placement work
- How to recognize and approach ricochet-prone work surfaces
- How to handle awkward position work (e.g., toe-nailing and work on ladders)
- How best to handle special risks associated with contact and single actuation triggers such as nail gun recoil and double fires. For example, coach new employees on how to minimize double fires by allowing the nail gun to recoil rather than continuing to push against the gun after it fires.
- What to do when a nail gun malfunctions.
*Training should also cover items covered in the following sections of the guidance, such as company nail gun work procedures, personal protective equipment, injury reporting, and fist aid and medical treatment .
You Should Know
- Training is important: Untrained workers are more likely to experience a nail gun injury than a trained worker.
- Training does not trump triggers: Trained workers using contact triggers still have twice the overall risk of injury as trained workers using sequential triggers.
3. Establish nail gun work procedures
Contractors should develop their own nail gun work rules and procedures to address risk factors and make the work as safe as possible. Examples of topics for contractor work procedures include but are not limited to the following Do’s & Don’ts:
DO’s
- Make sure that tool manuals for the nailers used on the job are always available on the jobsite.
- Make sure that manufacturers’ tool labels and instructions are understood and followed.
- Check tools and power sources before operating to make sure that they are in proper working order.
- Take broken or malfunctioning nail guns out of service immediately.
- Set up operations so that workers are not in the line of fire from nail guns being operated by co-workers.
- Check lumber surfaces before nailing. Look for knots, nails, straps, hangers, etc. that could cause recoil or ricochet.
- Use a hammer or positive placement nailer when nailing metal joinery or irregular lumber.
- For placement work, keep hands at least 12 inches away from the nailing point at all times. Consider using clamps to brace instead of your hands.
- Always shoot nail guns away from your body and away from co-workers.
-
Always disconnect the compressed air when:
- Leaving a nailer unattended
- Travelling up and down a ladder or stairs
- Passing the nail gun to a co-worker
- Clearing jammed nails
- Performing any other maintenance on the nail gun
-
Recognize the dangers of awkward position work and provide extra time and precautions:
- Use a hammer if you cannot reach the work while holding the nailer with your dominant hand.
- Use a hammer or reposition for work at face or head height. Recoil is more difficult to control and could be dangerous.
- Use a hammer or full sequential trigger nailer when working in a tight space. Recoil is more difficult to control and double fires could occur with contact triggers.
-
Take extra care with toe-nailing.
- Nail guns can slip before or during firing because the gun cannot be held flush against the work piece.
- Use a nail gun with teeth on the safety contact to bite into the work piece to keep the gun from slipping during the shot.
- Use the trigger to fire only after the safety contact piece is positioned.
-
Recognize the dangers of nail gun work at height and provide extra time and precautions:
- Set up jobs to minimize the need for nailing at height
- Consider using scaffolds instead of ladders
- If work must be done on ladders, use full sequential trigger nailers to prevent nail gun injuries which could occur from bumping a leg while climbing up or down a ladder.
- Position ladders so you don’t have to reach too far. Your belt buckle should stay between the side rails when reaching to the side.
- Maintain three points of contact with the ladder at all times to prevent a fall—this means that clamps may need to be used for placement work. Holding a nailer in one hand and the work piece with the other provides only two points of contact (your feet). Reaching and recoil can make you lose your balance and fall. Falls, especially with contact trigger nailers, can result in nail gun injuries.
Don’ts
-
Never bypass or disable nail gun safety features. This is strictly prohibited.
- Tampering includes removing the spring from the safety-contact tip and/or tying down, taping or otherwise securing the trigger so it does not need to be pressed. Tampering increases the chance that the nail gun will fie unintentionally both for the current user and anyone else who may use the nail gun. Nail gun manufacturers strongly recommend against tampering and OSHA requires that tools be maintained in a safe condition.
- There is NO legitimate reason to modify or disable a nail gun safety device.
-
Encourage workers to keep their fingers off the trigger when holding or carrying a nail gun.
If this is not natural, workers should use a full sequential nail gun or set down the nailer until they begin to nail again. - Never lower the nail gun from above or drag the tool by the hose.
- If the nail-gun hose gets caught on something, don’t pull on the hose. Go find the problem and release the hose.
- Never use the nailer with the non-dominant hand.
4. Provide Personal Protective Equipment (PPE)
Worker using recommended PPE when working with nail guns: hard hat, safety glasses, and hearing protection. Worker by OSHA is licensed under Public Domain
Safety shoes, which help protect workers’ toes from nail gun injuries, are typically required by OSHA on residential construction sites. In addition, employers should provide, at no cost to employees, the following protective equipment for workers using nail guns:
- Hard hats
- High Impact eye protection – safety glasses or goggles marked ANSI Z87.1
- Hearing protection – either earplugs or earmuff
5. Encourage reporting and discussion of injuries and close calls
Studies show that many nail gun injuries go unreported. Employers should ensure that their policies and practices encourage reporting of nail gun injuries. Reporting helps ensure that employees get medical attention. It also helps contractors to identify unrecognized job site risks that could lead to additional injuries if not addressed. Injuries and close calls provide teachable moments that can help improve crew safety.
If you have a safety incentive program, be sure that it does not discourage workers from reporting injuries. Employers that intentionally under report work-related injuries will be in violation of OSHA’s injury and illness recordkeeping regulation.
6. Provide fist aid and medical treatment
Employers and workers should seek medical attention immediately after nail gun injuries, even for hand injuries that appear to be minimal. Studies suggest that 1 out of 4 nail gun hand injuries can involve some type of structural damage such as bone fracture. Materials such as nail strip glue or plastic or even clothing can get embedded in the injury and lead to infection. Barbs on the nail can cause secondary injury if the nail is removed incorrectly. These complications can be avoided by having workers seek immediate medical care.
Worksite Story – A construction worker accidentally drove a 16 penny framing nail into his thigh. It didn’t bleed much and he didn’t seek medical care. He removed the nail himself. Three days later he felt a snap in his leg and severe pain. In the emergency room, doctors removed a sheared piece of nail and found that his thigh bone had fractured. Not all injuries are immediately visible. Failure to seek medical care can result in complications and more serious injuries.
Other Hazards
Air Pressure
Pneumatic tools and compressor use are regulated under OSHA’s Construction standard at 29 CFR 1926.302(b). The provisions in this standard that are relevant for nail guns are provided below:
1) Pneumatic power tools shall be secured to the hose or whip by some positive means to prevent the tool from becoming accidentally disconnected.
Note: An OSHA letter of interpretation allows the use of a quick disconnect with a pull-down sleeve to meet this requirement. It is composed of a male fitting (connector) and female fitting (coupling) that has a sleeve which must be pulled away from the end of the hose to separate the two fittings to prevent the tool from becoming accidentally disconnected.
3) All pneumatically driven nailers, staplers, and other similar equipment provided with automatic fastener feed, which operate at more than 100 p.s.i. pressure at the tool shall have a safety device on the muzzle to prevent the tool from ejecting fasteners, unless the muzzle is in contact with the work surface.
5) The manufacturer’s safe operating pressure for hoses, pipes, valves, filters, and other fitting’s shall not be exceeded.
6) The use of hoses for hoisting or lowering tools shall not be permitted.
Noise
Pneumatic nail guns produce short (less than a tenth of a second in duration) but loud “impulse” noise peaks: one from driving the nail and one from exhausting the air. Most nail gun manufacturers recommend that users wear hearing protection when operating a nailer.
Available information indicates that nail gun noise can vary depending on the gun, the work piece, air pressure, and the work setting. The type of trigger system does not appear to affect the noise level. Peak noise emission levels for several nailers ranged from 109 to 136 dBA.15,16 These loud short bursts can contribute to hearing loss. Employers should provide hearing protection in the form of earplugs or muff and ensure that they are worn correctly. Employers should also ask about noise levels when buying nail guns—studies have identified ways to reduce nail gun noise and some manufacturers may incorporate noise reduction features.
Note: OSHA’s standard for exposure to continuous noise levels (29 CFR 1926.52) addresses both the noise level and the duration of exposure. In this standard, workers exposed for 15 minutes at 115 A-weighted decibels (dBA) have the same exposure as workers exposed for 8 hours at 90 dBA.
The NIOSH and OSHA limit for impulse noise is 140 decibels: above this level a single exposure can cause instant damage to the ear.
NIOSH recommends that an 8-hour exposure should not exceed 85 dBA and a one-second exposure
should not exceed 130 dBA without using hearing protection. hearing protection.
Musculoskeletal disorders
Framing nail guns can weigh up to 8 pounds and many framing jobs require workers to hold and use these guns for long periods of time in awkward hand/arm postures. Holding an 8-pound weight for long periods of time can lead to musculoskeletal symptoms such as soreness or tenderness in the fingers, wrist, or forearm tendons or muscles. These symptoms can progress to pain, or in the most severe cases, inability to work. No studies have shown that one trigger type is any more or less likely to cause musculoskeletal problems from long periods of nail gun use. If use of a nail gun is causing musculoskeletal pain or symptoms of musculoskeletal disorders, medical care should be sought.
Conclusion
Nail gun injuries are painful. Some cause severe injuries or death. Nail gun injuries have been on the rise along with the increased popularity of these powerful tools. These injuries can be prevented, and more and more contractors are making changes to improve nail gun safety. Take a look at your practices and use this guide to improve safety on your job sites. Working together with tool gun manufacturers, safety and health professionals, and other organizations, we can reduce nail gun injuries.


9.9: Budgeted Balance Sheet
Learning Outcomes
- Create a budgeted balance sheet
Ok, one more piece of our puzzle to finish up! The balance sheet gives us a snapshot in time. In this case, a snapshot in our budgeted time. There are lots of pieces of the puzzle, so let’s take a few minutes to review:
One more reminder: \(\text{assets}=\text{liabilities}+\text{stockholder's equity}\)
This accounting equation may come in handy as we work through this process.
If sales, costs and expenses all follow the budget, here is what our year end balance sheet will look like!
| Hupana Running Company Budgeted Balance Sheet | ||
|---|---|---|
| Assets | ||
| Current Assets | ||
| Cash | $112,275 | |
| Raw Materials Inventory | $1,000 | |
| Finished Goods Inventory | $3,825 | |
| Total Current Assets | $117,050 | |
| Plant and Equipment | ||
| Land | $25,000 | |
| Buildings and Equipment | $50,000 | |
| Accumulated Depreciation | $(4,000) | |
| Plant and Equipment, Net | $71,000 | |
| Total Assets | $188,050 | |
| Liabilities and Owner’s Equity | ||
| Current Liabilities | ||
| Accounts payable | $ – | |
| Stockholder’s Equity | ||
| Common stock | $50,000 | |
| Retained earning | $138,050 | |
| Total stockholder’s equity | $188,050 | |
| Total liabilities and stockholder’s equity | $188,050 |
So overall, Hupana Running Company is in great shape if the budget goes as planned. But, budgets don’t always go as planned, so having a cash cushion is a great thing! They could have reduced sales, or price reductions and still be ok. They did a great job of creating a cushion, where if things happen, they will still be fine.
Most businesses make some changes during the year to the budget. The budget is a guide, and must be considered a fluid document, that can be changed as new information or situations occur.
Practice Questions


6.4: Analyzing Chords
When a three-note chord is represented by four or more notes (some of which are duplicates of the original three notes) and spread out across a grand staff, we can arrive at a lead-sheet symbol by answering three questions:
- What is the root of the chord?
- What is the quality of the chord (i.e., is the chord major, minor, diminished, or augmented)?
- What is the bass note (i.e., is the chord inverted)?
To determine the root of the chord, write all the notes only on the lines of the staff in treble clef (you may need to use ledger lines).
You could also choose to write all the notes only on the spaces in a staff.
The bottom note is the root when the chord is stacked as a triad. In this case, the root is DD.
Next, determine the quality of the triad (major, minor, diminished, or augmented) by analyzing if there is a M3 or m3 from the root to the 3rd, and if there is a M3 or m3 from the 3rd to 5th.
Since there is a m3 (3 half steps) from DD to FF and a M3 (4 half steps) from FF to AA, the triad is minor.
Finally, determine if the chord is inverted by checking to see if a note other than the root is the lowest note. Since the bass note (lowest note) is the root DD, the chord is not inverted. The chord is in root position, so the lead-sheet symbol is DmDm.
Now, try the process again.
On scratch paper, stack the notes only on lines in the treble clef to determine the root.
The root is EE.
Analyze the quality of the triad by measuring from EE to GG and from GG to BB♭.
It is an EE diminished triad (EE∘).
Finally, determine if the chord is inverted. Is the root (EE) the lowest note?
Since the lowest note is GG, the chord is inverted. Our lead-sheet symbol is EGE∘/G, which means we have an EE∘ chord with a GG in the bass.


6.4D: The FISH Technique
- Describe how fluorescent in situ hybridization (FISH) is used in clinical and biomedical studies to detect and localize the presence or absence of specific DNA sequences and to identify pathogens
FISH (fluorescence in situ hybridization) is a cytogenetic technique developed by biomedical researchers in the early 1980s. It is used to detect and localize the presence or absence of specific DNA sequences on chromosomes. FISH uses fluorescent probes bind to those targets that show a high degree of sequence complementarity. FISH can be used to detect RNA or DNA sequences of interest. FISH is often used for finding specific features in DNA for use in genetic counseling, medicine, and species identification. FISH can also be used to detect and localize specific RNA targets, including mRNAs, in cells. In this context, it can help define the spatial-temporal patterns of gene expression within cells and tissues.
Central to FISH are the use of probes. The probe must be large enough to hybridize specifically with its target but not so large as to impede the hybridization process. They are anti-sense to the target mRNA or DNA of interest, thus they hybridize to targets. The probe can be tagged directly with fluorophores, or with targets for flourescently labelled antibodies or other substrates. Different types of tags can be used, therefore different targets can be detected in the same sample simultaneously (multi-colour FISH). Tagging can be done in various ways, such as nick translation, or PCR using tagged nucleotides. Probes can vary in length from 20 to 30 nucleotides to much longer sequences.
FISH is often used in clinical studies. If a patient is infected with a suspected pathogen, bacteria from the patient’s tissues or fluids, are typically grown on agar to determine the identity of the pathogen. Many bacteria, however, even well-known species, do not grow well under laboratory conditions. FISH can be used to directly detect the presence of the suspect on small samples of the patient’s tissue. FISH can also be used to compare the genomes of two biological species, to deduce evolutionary relationships. A similar hybridization technique is called a zoo blot. Bacterial FISH probes are often primers for the 16s rRNA region. FISH is widely used in the field of microbial ecology, to identify microorganisms. Biofilms, for example, are composed of complex (often) multi-species bacterial organizations. Preparing DNA probes for one species and performing FISH with this probe allows one to visualize the distribution of this specific species within the biofilm. Preparing probes (in two different colors) for two species allows to visualize/study co-localization of these two species in the biofilm, and can be useful in determining the fine architecture of the biofilm.
Key Points
- FISH can be used in a clinical setting to identify pathogens or DNA / RNA targets of interest.
- FISH is used to detect and localize the presence or absence of specific DNA or RNA sequences in tissue or cells.
- FISH can also be used to compare the genomes of two biological species, such as in ecological studies, where a bacteria may not be culturable, it can be identified using FISH.


6.11: A Comparison between Biological Reactions and Laboratory Reactions
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Objectives
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Key Terms
Make certain that you can define, and use in context, the key term below.
- enzyme
Study Notes
This section is a brief (but perhaps interesting) overview of some of the key differences between reactions performed in the lab and those in living systems. At this point, do not concern yourself with memorizing large biological molecules and reactions.
The Active Site
A critical element in the three-dimensional structure of any enzyme is the presence of an ‘ active site’ , which is a pocket, usually located in the interior of the protein, that serves as a docking point for the enzyme’s substrate (s) (‘substrate’ is the term that biochemists use for a reactant molecule in an enzyme-catalyzed reaction). It is inside the active site pocket that enzymatic catalysis occurs. Shown below is an image of the glycolytic enzyme fructose-1,6-bisphosphate aldolase, with its substrate bound inside the active site pocket.
When the substrate binds to the active site, a large number of noncovalent interactions form with the amino acid residues that line the active site. The shape of the active site, and the enzyme-substrate interactions that form as a result of substrate binding, are specific to the substrate-enzyme pair : the active site has evolved to 'fit' one particular substrate and to catalyze one particular reaction. Other molecules do not fit in this active site nearly so well as fructose 1,6-bisphosphate.
Here are two close-up views of the same active site pocket, showing some of the specific hydrogen-bonding interactions between the substrate and active site amino acids. The first image below is a three-dimensional rendering directly from the crystal structure data. The substrate is shown in 'space-filling' style, while the active site amino acids are shown in the 'ball and stick' style. Hydrogens are not shown. The color scheme is grey for carbon, red for oxygen, blue for nitrogen, and orange for phosphorus.
Below is a two-dimensional picture of the substrate (colored blue) surrounded by hydrogen-bonding active site amino acids. Notice that both main chain and side chain groups contribute to hydrogen bonding: in this figure, main chain H-bonding groups are colored purple, and side chain H-bonding groups are colored green.
Looking at the last three images should give you some appreciation for the specific manner in which a substrate fits inside its active site.
Transition State Stabilization
One of the most important ways that an enzyme catalyzes any given reaction is through entropy reduction: by bringing order to a disordered situation (remember that entropy is a component of Gibbs Free Energy, and thus a component of the activation energy). Let’s turn again to our previous example (from section 6.1C) of a biochemical nucleophilic substitution reaction, the methylation of adenosine in DNA. The reaction is shown below with non-reactive sections of the molecules depicted by variously shaped 'bubbles' for the sake of simplicity.
In order for this reaction to occur, the two substrates (reactants) must come into contact in precisely the right way. If they are both floating around free in solution, the likelihood of this occurring is very small – the entropy of the system is simply too high. In other words, this reaction takes place very slowly without the help of a catalyst.
Here’s where the enzyme’s active site pocket comes into play. It is lined with various functional groups from the amino acid main and side chains, and has a very specific three-dimensional architecture that has evolved to bind to both of the substrates. If the SAM molecule, for example, diffuses into the active site, it can replace its (favorable) interactions with the surrounding water molecules with (even more favorable) new interactions with the functional groups lining the active site.
Depiction of SAM bound in active site of enzyme
In a sense, SAM is moving from one solvent (water) to another 'solvent' (the active site), where many new energetically favorable interactions are possible. Remember: these new contacts between SAM and the active site groups are highly specific to SAM and SAM alone – no other molecule can ‘fit’ so well in this precise active site environment, and thus no other molecule will be likely to give up its contacts to water and bind to the active site.
The second substrate also has a specific spot reserved in the active site. (Because in this case the second substrate is a small segment of a long DNA molecule, the DNA-binding region of the active site is more of a 'groove' than a 'pocket').
So now we have both substrates bound in the active site. But they are not just bound in any random orientation – they are specifically positioned relative to one another so that the nucleophilic nitrogen is held very close to the electrophilic carbon, with a free path of attack. What used to be a very disordered situation – two reactants diffusing freely in solution – is now a very highly ordered situation, with everything set up for the reaction to proceed. This is what is meant by entropy reduction: the entropic component of the energy barrier has been lowered.
Looking a bit deeper, though, it is not really the noncovalent interaction between enzyme and substrate that are responsible for catalysis. Remember: all catalysts, enzymes included, accelerate reactions by lowering the energy of the transition state . With this in mind, it should make sense that the primary job of an enzyme is to maximize favorable interactions with the transition state, not with the starting substrates. This does not imply that enzyme-substrate interactions are not strong, rather that enzyme-TS interactions are far stronger , often by several orders of magnitude. Think about it this way: if an enzyme were to bind to (and stabilize) its substrate(s) more tightly than it bound to (and stabilized) the transition state, it would actually slow down the reaction, because it would be increasing the energy difference between starting state and transition state. The enzyme has evolved to maximize favorable noncovalent interactions to the transition state : in our example, this is the state in which the nucleophilic nitrogen is already beginning to attack the electrophilic carbon, and the carbon-sulfur bond has already begun to break.
In many enzymatic reactions, certain active site amino acid residues contribute to catalysis by increasing the reactivity of the substrates . Often, the catalytic role is that of acid and/or base. In our DNA methylation example, the nucleophilic nitrogen is deprotonated by a nearby aspartate side chain as it begins its nucleophilic attack on the methyl group of SAM. We will study nucleophilicity in greater detail in chapter 8, but it should make intuitive sense that deprotonating the amine increases the electron density of the nitrogen, making it more nucleophilic . Notice also in the figure below that the main chain carbonyl of an active site proline forms a hydrogen bond with the amine, which also has the effect of increasing the nitrogen's electron density and thus its nucleophilicity ( Nucleic Acids Res . 2000 , 28 , 3950 ).
How does our picture of enzyme catalysis apply to multi-step reaction mechanisms? Although the two-step nucleophilic substitution reaction between 2-chloro-2-methylpropane and the cyanide anion is not a biologically relevant process, let’s pretend just for the sake of illustration that there is a hypothetical enzyme that catalyzes this reaction.
The same basic principles apply here: the enzyme binds best to the transition state. But therein lies the problem: there are two transition states! To which TS does the enzyme maximize its contacts?
Recall that the first step – the loss of the chloride leaving group to form the carbocation intermediate – is the slower, rate-limiting step. It is this step that our hypothetical enzyme needs to accelerate if it wants to accelerate the overall reaction, and it is thus the energy of TS1 that needs to be lowered.
By Hammond’s postulate, we also know that the intermediate I is a close approximation of TS1. So the enzyme, by stabilizing the intermediate, will also stabilize TS1 (as well as TS2) and thereby accelerate the reaction.
If you read scientific papers about enzyme mechanisms, you will often see researchers discussing how an enzyme stabilizes a reaction intermediate. By virtue of Hammond's postulate, they are, at the same time, talking about how the enzyme lowers the energy of the transition state.
An additional note: although we have in this section been referring to SAM as a 'substrate' of the DNA methylation reaction, it is also often referred to as a coenzyme , or cofactor . These terms are used to describe small (relative to protein and DNA) biological organic molecules that bind specifically in the active site of an enzyme and help the enzyme to do its job. In the case of SAM, the job is methyl group donation. In addition to SAM, we will see many other examples of coenzymes in the coming chapters, a number of which - like ATP (adenosine triphosphate), coenzyme A, thiamine, and flavin - you have probably heard of before. The full structures of some common coenzymes are shown in table 6 in the tables section.


7.1: Vocabulary
In this section
- You will learn new vocabulary that relate to daily routine.
- You will practice using new words and verbs in different contexts.
Vocabulary (1)
Listen to new vocabulary and repeat as you follow along in the list of words underneath. Listen as many times for fluency.
[table id=51 /]
Activate your new vocabulary through the following section.
Vocabulary (2)
Listen to new vocabulary and repeat as you follow along in the list of words underneath. Listen as many times for fluency.
[table id=52 /]
Notes on vocabulary
Some verbs have morphological rules that affect their conjugations. Learn how to conjugate the verb “To come” and “to wake up” in the present and past.
[table id=53 /]
Activate your new vocabulary and use of new verbs in the following section.
Key Takeaways
- You have more control on verb forms and use.