Abstract
Pneumatic framing nail gun use is ubiquitous throughout the modern homebuilding industry. This tool has dramatically increased framing productivity beyond what could be achieved with a hand hammer. However, the dramatic increase in productivity introduced a new injury: You're using a gun to do something faster, and fast isn't safe. . . . It might be making it easier, but all around, it's shooting a projectile at a high speed to go through hard materials. It's just dangerous to work with. (Union carpenter, St. Louis, MO) Before pneumatic nail guns were available, nail puncture injuries on a construction site typically occurred when a carpenter or other tradesperson stepped on a nail protruding from a piece of lumber. Carpenters did not accidentally drive nails into their own bodies or that of a coworker with repeated strikes from a hammer. However, such injuries became more common when pneumatic nail guns were introduced to drive nails at a high speed to go through hard materials. Pneumatic nail guns have a safety device (workpiece contact, nose, yoke, tip) at the end of the gun muzzle that must be depressed before the fastener can be discharged. Generally, these devices have two types of trigger systems that then define how the nail gun fires in response to a trigger press: 1) The sequential actuation trigger (SAT) requires that each nail can only be discharged when the safety tip is first depressed and, while held depressed, the trigger is squeezed. 2) The contact actuation trigger (CAT) allows the operator to first squeeze the trigger and, while holding the trigger squeezed, repeatedly bump the safety tip on the workpiece to shoot multiple nails. Of these two trigger mechanisms, the SAT provides a positive safety advantage (European Committee for Standardization, 2009; Stanley Works, 2002) in that it prevents the unintended firing of a nail that can otherwise occur when the trigger is depressed and the workpiece contact is bumped. Traumatic injuries can occur when an operator using either type of actuation device intentionally discharges a nail that subsequently penetrates through the wood or misses it altogether. However, an SAT-equipped nail gun is much less likely to be discharged unintentionally, as the trigger must be activated while the safety tip is depressed against the workpiece (NIOSH/OSHA, 2011). Unintentional nail discharge using a CAT-equipped device typically occurs following nail gun recoil (resulting in a double fire - a second, unintended shot) or when the operator has his/her finger on the trigger and the nail gun nose inadvertently contacts an object (Lipscomb, Dement, Nolan, et al., 2003). Although operators are advised to not hold the trigger in the depressed position when not intending to shoot a nail, a nail gun's physical characteristics, including weight (8 lb to 9 lb), balance, trigger location and hand-grip design, make it easier to hold the gun with a full power grip that includes the index finger.
