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 24, 1997

Robert Hofer, C.I.H.
Safety/Industrial Health Engineer
Goodyear Tire & Rubber Company
1144 E. Market Street
Akron, Ohio 44316

Dear Mr. Hofer:

This is in response to your letter of October 28, 1996, regarding placement of the noise dosimeter microphone for measuring the noise exposure of an employee using an airline respirator equipped with a shroud.

You informed us that the airline respirator is required for protecting the employee from carbon dioxide and dust when certain equipment is operated. In addition to these air contaminates, the job produces noise sound levels above the exposure limits. You believe you have exhausted all engineering controls based on current technology, but the noise exposure remains above the permissible limit. During your discussion about engineering controls you mentioned the noise level inside the airline respirator helmet when the airline respirator is included as an engineering control. Please be aware that the Occupational Safety and Health Administration (OSHA) does not consider an airline respirator an engineering control for either air contaminants or noise. Any noise attenuation provided by an airline respirator cannot be credited toward meeting the requirement to utilize feasible engineering or administrative controls to reduce sound levels within the exposure limits.

You performed a series of 19 simultaneous measurements of the noise levels inside and outside the respirator hood when certain equipment was operated. The mean sound level you measured outside the hood was less than 105 dBA as opposed to the mean sound level of less than 95 dBA that you measured inside the hood. Given these findings you believe that the proper location for the noise dosimeter microphone for evaluating an employee's noise exposure is inside the respirator hood. You have requested the position of the Occupational Safety and Health Administration (OSHA) on this matter.

OSHA agrees with locating the noise dosimeter microphone inside the respirator hood for the purpose of determining exposure levels and the noise attenuation required by hearing protectors provided you show you are measuring the actual noise exposures occurring inside the respirator hood and you demonstrate that the amount of noise exposure attenuation provided by the respirator hood is reasonably consistent. For example, you need to determine whether factors such as how the respirator hood is donned and positioned by the wearer, and the direction the respirator wearer faces with respect to the noise source affect the noise attenuation provided by the respirator hood. If the noise exposure attenuation afforded by the respirator hood is not consistent it is possible for the respirator hood to be providing exceptional attenuation of the noise exposure on the day you measure the noise exposure inside the hood and mislead you to conclude that the noise exposure inside the hood on other occasions is lower than it actually is.

During a telephone conversation after we received your letter you asked that we state whether the calculated noise attenuation values for hearing protectors have to be reduced by 50 percent when determining whether they provide adequate protection. If the hearing protectors are properly fitted and worn, the calculated attenuation values for them do not have to be reduced by 50 percent when determining whether they provide adequate attenuation to comply with 29 CFR 1910.95(j)(2) or (j)(3).

We appreciate the opportunity to clarify our position for you. If you have further questions please contact the Office of Health Compliance Assistance at (202) 219-8036.


Steve Mallinger, Acting Director
Office of Health Compliance Assistance


TO:       Ruth McCully, Director
                Office of Health Compliance Assistance
                Occupational Safety and Health Administration
                200 Constitution Ave., N.W.
                Washington D.C.  20210

FROM:     R. Hofer, C.I.H.
                Safety/Ind. Health Engineer
                Goodyear Tire & Rubber Co. 
                1144 E. Market St.
                Akron, Ohio  44316

DATE:     October 28, 1996

SUBJECT:  Clarification of 1910.95 Standard, paragraph(d)


The Goodyear Tire & Rubber Co. is experimenting with a new technology. Testing has been completed in-house to determine the potential hazards our employees may be exposed while using this device. A twenty-three (23) point program has been drafted to protect the safety and health of our associates. The major concern with the equipment and its use is the sound level created which is greater than 100 dBA.

We are requesting from OSHA a letter of interpretation on the placement of the noise dosimeter microphone. We believe that the placement should be inside an airline respirator hood while collecting a personal exposure sample. This would be representative of the workers actual noise exposure, as with the welding fume and sandblasting monitoring interpretation (i.e., sampling within the welding or sandblasting hood).


OSHA requires that the dosimeter microphone be placed within a two-foot diameter sphere surrounding the head when conducting the monitoring. It also states that it should be placed in the employees hearing zone (CPL. 2-2.35A). Further, through communication with several OSHA inspectors it has been indicated that the placement of the noise dosimeter microphone would be outside any head covering. There does not appear to be any documentation as to the proper placement when a hood is used.

Goodyear has had a Hearing Conservation Program that requires monitoring, education, audiometric testing/evaluation and recordkeeping as the major components. This program has been in place for many years, even prior to the Federal Hearing Conservation Amendment promulgation.

Concerning this job, the Job Safety Analysis procedure requires the operator to use hearing protector inserts with a minimum NRR of 30 dB and an airline respirator equipped with a shroud. The purpose of the respirator is to protect against carbon dioxide and dust exposures.

Initial noise measurements using this equipment resulted in outside the helmet readings of 116-120 dBA. We have consulted with the vendor and their noise engineers who have completed the following equipment modifications.

1. Nozzle pressure was reduced to an optimum pound/square inch.
2. Pellet pressure was reduced to an optimum pounds/square inch.
3. The nozzle configuration was internally modified.
4. The barrel length and configuration were modified.
5. Designed a muffler but was not successful due to the speed of release and particle size.

These modifications have reduced the mean sound level too less than 105 dBA outside the respirator helmet. When the helmet (an airline respirator) is included as an engineering control, the mean sound level inside the helmet is less than 95 dBA. Using the inside exposure level would allow the operator to work up to at least 8 hours while wearing hearing protection with a 30 dB NRR, rather than one hour based on outside the helmet testing of 105 dBA.

We believe we and the vendors have exhausted all engineering controls based on current technology. The sound levels have been reduced from 123 dBA to 102 dBA. We have also contacted the OSHA Chicago Technical Support group and tried several of their suggestions without any further reduction.

The following table summarizes the noise dosimetry data from nineteen (19) trials.

|                           |                    |                   |
|Noise dosimtry results     |80 dB threshold |90 dB threshold|
|for the exposure period*:  |     (Leq=dBA)      |      (Leq=dBA)    |
|                           |                    |                   |
|   inside respirator       |                    |                   |
|     hood (range):         |    92.7-100.4      |     91.2-100.6    |
|                           |                    |                   |
|       Mean Level          |        93.5        |       94.5        |
|                           |                    |                   |
| outside respirator hood   |                    |                   |
|       (range) :           |      98.7-106      |    98.4-106.0     |
|                           |                    |                   |
|        Mean level         |        102.3       |        102.1      |

*NOTE: The sampling period ranged from 12-42 minutes.


After conducting numerous trials and evaluation of audiograms, we feel the employee's hearing can best be protected by evaluating the noise exposure inside the respirator helmet. For this reason, we are requesting a letter of interpretation from OSHA that would allow us to evaluate the employee's noise exposure inside of, rather than outside, the helmet.

Questions can be directed to my attention on 330/796-1950.


Robert Hofer