OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

February 22, 1985

                 Deputy Assistant Secretary 

THRU:            ED BAIER 
                 Directorate of Technical Support

                 Deputy Director
                 Directorate of Technical Support

SUBJECT:         Chocolate Manufacturer's Association (CMA)
                 Noise Petition

Summary CMA Petition

The CMA has petitioned OSHA to adopt a new sampling technique for measuring noise exposures. The CMA states that the procedure is more "accurate" because the dosimeter circuitry can integrate the exact time of very short duration peak noise. They are urging the agency to adopt this procedure because it would result in a reduction of "measured exposure" that impulse noise now adds to any continuous noise present. However, whether this reduction should be granted because employees exposed to impulse noise under the present exposure monitoring technique overstates their exposure from a dose response relationship is not clear. In addition, the conversion to fast response dosimeters would result in significant equipment modification costs to the agency and the private sector. The task of gathering additional information and investigating whether this new technique should be incorporated would preferably involve the Directorates of Health Standards Programs and Technical Support. The agency may have to seek input from the public due to the significance of this change to the present procedure. The NBS study will help the agency to better understand impulse versus continuous monitoring results but will not generate information on biological effects. Staff from the Directorates of Health Standards Programs, Field Operations and Technical Support have provided comments into this response.

The CMA's petition merely argues that a fast response would be a more accurate measurement technique. They argue that this technique would result in lower exposure readings for their employees. However, they do not address whether this lessening of exposure results also indicates that their employees are at less risk. A vast majority of studies that the standard was based upon were with instruments using the A-scale, slow response. Changing the technique of instrument sampling would result in unknown health effects.

The OSHA current noise standard includes the original Walsh-Healey regulations 1910.95(a)-(b) and the 1981 promulgated Hearing Conservation Amendment. Both require noise levels to be measured on the A-scale, slow response. Measuring sound pressure level on the A-scale, slow response was a technique developed many years ago. New technological equipment is now available (or could be readily available to the public) that can measure and record the exact time duration of a sudden or very brief impulse or impact noise. This equipment was not available when the original Walsh-Healey standard was recommended in the 1960s. If this new or modified equipment and different measuring technique could be used in industry, the exposure readings from some industry operations could be considerably less.


The current government and industry noise measuring procedures date back prior to the time dosimeters were available and all noise level measurements were taken with a sound level meter and recorded manually. The slow response circuit was adopted to integrate the noise pulses so that the human eye could more easily read the meter output. However, since that time, audio dosimeters have been developed that automatically measure, record and integrate this information for a full work shift. More recently, advanced circuitry has been developed that could very rapidly measure the exact sound profile of a peak for very brief or sudden noise. For example, the banging together of two metallic objects may indicate on a sound level meter set to the slow response, a one-two second level above 90 or 100 dB. This same event measured on the fast response may only indicate the same or higher exposure for 0.5 second. Assuming this type of noise may occur several thousand times per day in an industrial environment, the daily integrated exposures measured both ways would give significantly different results. The CMA has asked OSHA to change its measuring techniques because they believe that this new technique will give a more accurate picture of industry noise exposures.

Prior to the agency promulgating the Hearing Conservation Amendment (HCA) the agency attempted to distinguish between continuous noise (i.e., noise lasting greater than one second) and intermittent or impact noise) peak noise less than one second). Instructions were included in the Industrial Hygiene Field Operations Manual for estimating the contribution that impact noise would add to dosimeter reading. However, the HCA specifically addressed this type of noise exposure and stated that impulse noise should be combined with continuous noise for the purposes of calculating employee noise exposure. This decision was based on evidence that impulse noise is certainly as hazardous and may be more hazardous than continuous noise.

After the HCA was published, the Industrial Hygiene Technical Manual was revised and all references to separating out continuous versus impulse noise were deleted. The references in CMA's petition describing the distorting effects of short duration impulses are merely informational bulletins developed by the Cincinnati Laboratory and placed in the back of the manual. The present agency policy for determining personal noise exposure is to use the dosimeter incorporating an A-scale slow response mechanism for all types of noise.

Health Effects

Although the HCA was vacated by the Courts, it contains a useful and extensive review of past occupational noise surveys and attempts to correlate dose and response. In the case of impulse noise, impulse noise has generally been superimposed on moderate-to-high levels of continuous noise and exposures resulted in detrimental effects. Since instrumentation, until very recently, has not been available that would minimize the contribution that impulse noise adds to continuous noise exposure, very few health studies exist that could clearly separate out the precise biological effects of just impulse noise. A few studies indicate impulses superimposed on background noise resulted in exacerbated hearing loss.

National Bureau of Standards (NBS) Study

OSHA contracted with NBS in 1984 for $150,000 to conduct a study that would more clearly indicate the contribution impulse noise may add to continuous noise using the A-scale, slow response. The final results of this study will be made available around May 1, 1985. The work that NBS will produce will certainly add to the agency's understanding of how impulse noise interacts with the measuring of all noise with slow response.

Other Issues

Discussions with members of the ACGIH and ANSI Committee representatives concerning this new measurement technique produced little more information. Individuals stated that both ACGIH and ANSI presently recommend to sample noise using OSHA's present technique. The representatives felt uncomfortable in changing this technique unless sufficient health data were available so that they could clearly separate out and understand just how the short duration impulse noise contributes to hearing loss. They felt that while the technology is now available, the biological understanding of whether impulse noise should be given less weight (incorporating fast response) or more weight (adding multiplier circuits) is not available. They stated that until this relationship develops, they must use the present technique because this is the basis of their current recommended exposure levels.

From an agency cost standpoint, Dave Loebach of the Cincinnati Laboratory estimates that some (less than 50 percent) of the dosimeters could be converted. However, conversion costs would be as high as $100-200 per unit including software replacement. However, approximately 1,700 of the DuPont D-376 and 2,700 of the GenRad 1954 dosimeters are probably not convertible. Total conversion and replacement costs would be substantial (greater than $500,000).