A person wanting protection from noise levels of 120+ dBA due to a steel hammer forge will want a protector with a high amount of noise reduction; usually dual protection as recommended by NIOSH (1998) and verified by an AIHA case study (http://www.aiha.org/votp_NEW/study/hearing.html).
A person needing protection from steady-state background noise levels of 92 dBA will want a protector that provides enough noise reduction to prevent noiseinduced hearing lost (NIHL), but not so much as to cause isolation from the general environment (NIOSH, 1998).
OSHA’s Field Manual states, “The actual effectiveness of any individual hearing protector cannot be determined under workplace conditions. However, OSHA's noise standards (1910.95(j)(2) and 1926.52(b)) require that personal hearing protection be worn to attenuate the occupational noise exposure of employees to within the limits shown in Tables G-16, G-16a, and D-2, respectively.
“Hearing protectors are evaluated under laboratory conditions specified by the American National Standards Institute in ANSI S3.19-1974 (OSHA's experience and the published scientific literature indicate that laboratory-obtained real ear attenuation for hearing protectors can seldom be achieved in the workplace).” The manual then provides instructions for applying an NRR that has been divided by two.
NIOSH, in the revised Noise Criteria Document (1998) recommends derating HPDs with different values depending on the type of protector they are. The recommended derating for earmuffs is 25 percent, for slow-recovery foam earplugs it’s 50 percent, and for all other earplugs and semi-insert devices it’s 75 percent (NIOSH, 1998).
Further studies have shown that the amount by which the NRR over-estimates the actual noise reduction provided by a hearing protector is not simply a matter of type. The amount is unique to each protector. Thus, for earplug A an appropriate derating may be 30 percent, while for earplug B it may be 150 percent (Franks et al., 2000).
Because of these problems, due in part to the EPA’s incorporation of the experimenter fit method of ANSI S3.19-1979 that required the experimenter fit the earplugs into or earmuffs over the ears of the subject being tested, the EPA decided to review the rule. As well, a sufficient number of laboratory and field studies had been done and the ANSI standards had been revised to support the development of a new labeling rule (Royster, 1996; Murphy et al., 2008)
The old EPA rule provided a single-number rating and implied by its statistical methods that more than 98 percent of wearers would experience the amount of noise reduction on the label. The proposed revision has been switched to two numbers as part of a Noise Reduction Range. The lowest number is supposed to convey the amount of noise reduction that 80 percent of wearers wound receive while the upper number supposed to convey he amount of noise reduction that only 20 percent of the wearers would received. An example of the label for passive HPDs appears below: The lower NRR is 18 and the higher NRR is 32. dB
For HPDs designed to allow sound to a certain level to reach the ear regardless of the sound outside the HPD, the new proposed EPA rule calls for two NRR ranges. One would be the same passive range as if the electronics turned off. The other would be the range with the protector turned on. So for the example in Figure 2 below, the passive NRR range is from 11 to 20 while the active NRR range is from 15 to 22 dB.
For HPDs designed to protect from impulsive noise, such as weapons fire and drop hammer forges, there is a proposed label as shown in Figure 3. The device is tested passively and its NRR range is between 22 and 35, while when the impulse characteristics of the HPD are considered, the NRR range changes to 11 to 25 dB.
All in all, it would seem the newly proposed hearing protector labeling rule addresses most of the shortcomings of the previous rule. Whereas the previous rule could account for only the passive attenuation of HPDs, the new rule accounts for those with electronic circuits to either let outside sound come in at a safe level or to cancel the incoming sound.
Also, the older rule required that a hearing protector be testing only once during its sales life unless the materials or manufacturing processing changed. The new rule requires retesting every five years unless there is a change in the HPD that would require retesting sooner. And, the EPA reserves the right to conduct a compliance audit for any reason.
What’s still wrong: The only problem with the new rule is its continued reliance on the experimenter-supervised fit (Method A) for the testing of the protector’s passive NRR range. Studies have shown that not only does the experimenter-supervised fit method result in NRRs that are higher than the typical wearer will realize, there is also a laboratory effect so the results may vary in a statistically significant amount from one laboratory to another. The subject-fit method of the present standard (ANSI S3.12-2008), usually referred to as Method B, provides NRR values that most closely predict what the wearers will achieve and will also allow the greater reproducibility of results between testing facilities.
ANSI S3.19-1974 Standard for the Measurement of Real- Ear Hearing Protector Attenuation and Physical Attenuation of Earmuffs
ANSI 12.6–2008, Method A, Real Ear Attenuation at Threshold (REAT)
ANSI S12.42-1995 (R2004) Microphone-in-Real-Ear and Acoustic Test Fixture Methods for the Measurement of Insertion Loss of Circumaural Hearing Protection Devices.
Berger, E, Franks JR, and Lindgren, F. (1996) International review of field studies of hearing protector attenuation. In: Axlesson A, Borchgrevink H, Hamernik RP, Hellstrom P, Henderson D, Salvi RJ, editors. Scientific basis of noise-induced hearing loss. New York, NY: Thieme Medical Publishers, Inc. pp. 361–77.
Franks JR, Murphy WJ, Harris DA et al . (2003) Alternative field methods for measuring hearing protector performance. AIHA J (Fairfax, Va); 64: 501–9.
NIOSH (1998) NIOSH Publication No. 98-126: Criteria for a Recommended Standard: Occupational Noise Exposure
Royster, Julia D. et al., ‘‘Development of a New Standard Laboratory Protocol for Estimating the Field Attenuation of Hearing Protection Devices. Part I. Research of Working Group 11, Accredited Standards Committee S12, Noise,’’ Journal of the Acoustical Society of America, 99(3):1506– 1526, March 1996.