Occupational noise exposure limits

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

April 1, 1991
David L. George, P.E.
Manager, Regulatory Requirements
Unisys Corporation
[Recipient address omitted]
Dear Mr. George:
This is in response to your letter of February 8, 1991, concerning the telephone equipment standard designated UL 1459 issued by Underwriters Laboratories, Inc. (UL)
The standard establishes limits for maximum acoustic pressure and for peak acoustic pressure emanating from a receiver of a telephone or similar device. You inquired whether these limits are higher than the occupational noise exposure limits established by the Occupational Safety and Health Administration (OSHA).
The UL provision for maximum acoustic pressure states:

In any operating state, during reasonable operation of the unit, the maximum acoustic pressure emanating from a receiver earpiece of a telephone or similar device shall not exceed 125 dBA (relative to 20 micro-Pascals) for supra-aural (on-ear) handsets, 121 dBA for insert type (in-ear) earphones, or 118 dBA for supra-aural headphones.

The UL limits for maximum acoustic pressure are higher than OSHA's exposure limit for continuous noise. OSHA prohibits any exposure to continuous noise exceeding 115 dBA sound level.
The UL provision for peak acoustic pressure states:

The peak acoustic pressure emanating from the receiver earpiece shall not exceed 140 dB (relative to 20 micro- Pascal) with the unit in any operating state, or with a voltage surge of 800 V peak open circuit, (either polarity), having a 10 microsecond rise time to crest and a minimum decay time to half crest of 560 microseconds, and a minimum current of 10 A peak (short circuit), and applied between the tip and ring terminals of the unit.

The OSHA limit for impulsive or impact noise is also 140 dB peak sound pressure level. This limit is independent of the duration of the noise impulse. There is no OSHA limit for number of exposures to impulsive or impact noise. Impulsive or impact noise must be integrated into the measurement of continuous noise exposure, however.
The UL provision for peak acoustic pressure also states:

"Peak hold" is defined as an acoustic response having a duration less than 50 microseconds.

You commented that this is an unclear and probably incorrect definition for impulse. We do not believe it is a definition for impulse, but instead, it appears to be a response time requirement for the instrument used to measure impulsive or impact noise. For example, the specification for the General Radio type 1556-B impact-noise analyzer states:

Peak Reading: Rise time is less than 50 microseconds for a value within 1 dB of peak value (for rectangular impulses).

You asked what should be done about those situations where the UL requirements are not sufficiently stringent to assure that OSHA employee protection requirements are not violated. It would be helpful if those situations were eliminated by making the UL requirements more stringent, but OSHA has no legal authority to intervene. Nevertheless, employers have a legal responsibility to comply with OSHA standards and may not rely on industry or consensus standards when such standards are less protective than those promulgated by OSHA.
Thank you for contacting OSHA regarding this matter.
Sincerely,
Patricia K. Clark, Director
Directorate of Compliance Programs

[Requester letter reproduced on OSHA page; omitted here.]