Why are we interested in impulsive noise? Short duration impulsive noise is typically generated by a release of pressure (impulse) or a collision of solid objects (impact). In animal models these noises have been shown to be more damaging to the ear than continuous noise of equal energy (Hamernik and Henderson 1974, Dunn, Davis et al. 1991, Hamernik, Ahroon et al. 1994). Impulsive noises are common in manufacturing, construction, public service and the military. All police and sheriff officers must qualify annually on firearms which generate impulsive noise. What is an impulsive noise? The US Occupational Safety and Health Administration (OSHA) definition of impulsive noise includes noises most researchers do not consider impulsive: "If the variations in noise level involve maxima at intervals of 1 second or less, it is to be considered continuous." That is, if maxima are 1 second or less, noises are considered impulsive. Most researchers would consider a noise impulsive if it is a single pressure peak typically lasting milliseconds to microseconds. How do we measure impulsive noises? The use of standard industrial hygiene noise dosimeters to measure impulsive noises is inappropriate (Kardous and Willson 2004). Dosimeter electronics "clip" at high input levels and do not have a fast enough time constant to capture impulses. Many sound level meters may be able to capture peak levels with a peak hold circuit depending upon the microphone and amplifier. For about the past 10 years the National Institute for Occupational Safety and Health (NIOSH) has been developing a portable measurement system to measure firearm discharges and other impulsive noise. The directional nature of impulsive sounds may require multiple sensors to capture the sound. One approach is to use a stand-alone probe with multiple microphones separated by well-known distances in a calibrated capsule such as the G.R.A.S. (Holte, Denmark) sphere. This probe consists of four matched G.R.A.S. ¼", 40-BH pressure microphones in a 1"-diameter machined aluminum sphere. The four preamplifiers for the microphones are located inside the sphere. However, the sphere itself may affect the measurement. What to measure for risk analysis? In the pre-digital days a microphone attached to a storage oscilloscope captured the configuration of the impulsive noise. The dimensions that are easily measured on an oscilloscope screen are peak pressure level and duration. A number of conventions have evolved to characterize impulses: A, B, C and D duration, etc. Although codified into American National Standards Institute (ANSI) and International Standards Organization (ISO) standards and even law, there is little evidence to correlate any of these dimensions with risk of hearing loss. OSHA and NIOSH indicate that no one should be exposed to impulses in excess of 140 dBA.
We take your privacy seriously. You can review and change the way we collect information below.
These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. They help us to know which pages are the most and least popular and see how visitors move around the site. All information these cookies collect is aggregated and therefore anonymous. If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance.
Cookies used to make website functionality more relevant to you. These cookies perform functions like remembering presentation options or choices and, in some cases, delivery of web content that based on self-identified area of interests.
Cookies used to track the effectiveness of CDC public health campaigns through clickthrough data.
Cookies used to enable you to share pages and content that you find interesting on CDC.gov through third party social networking and other websites. These cookies may also be used for advertising purposes by these third parties.