Impulsive/impact noise is typically generated by the rapid release of compressed gases (impulse) or the collision of solid objects (impact) and is defined as the instantaneous change in sound pressure over a short period of time. Examples may include the impact of two metal objects, or the shooting of a firearm. The standard states that exposure to impulsive or impact noise should not exceed a 140-dB peak sound pressure level. Impulsive or impact noises are considered to be much more harmful to hearing than continuous noises. In construction, most of the 500,000 workers who are exposed to hazardous noise levels are also exposed to impulsive and impact noise sources on worksites. Impulsive and impact noise is typified by a sound that rapidly rises to a sharp peak and then quickly fades. Both are transient noises of brief duration and high intensity. The sound may or may not have a "ringing" quality (such as a striking a hammer on a metal plate or a gunshot in a reverberant room). Impulsive noise can be repetitive or a single event (like a sonic boom); if impulses occur in very rapid succession (such as with some jack hammers), it is not described as impulsive or impact noise.
Many SLMs also have "peak" and "impulse" response settings for measuring transient sounds (sounds that decay or pass with time). These settings are not interchangeable; the true peak value is the maximum value of the noise waveform, while the impulse measurement is an integrated measurement. It is appropriate to use the true peak reading only when determining compliance with OSHA's 140-dB peak (instantaneous) sound pressure level [29 CFR 1910.95(b)(1) or 29 CFR 1926.52(e)]. Avoid using the impulse response setting when measuring true peak sound pressure levels.
An alternate method of interrupting the noise path is to relocate the noise source. For example, air expansion at valves can cause significant noise; these valves can be routed to an area away from the worker by extending the piping, which would remove the noise source from the worker, thereby reducing the worker's noise exposure. 2b1af7f3a8