Standard Interpretations - Table of Contents Standard Interpretations - Table of Contents
• Standard Number: 1910.95(a)


April 1, 1991

David L. George, P.E.
Manager, Regulatory Requirements
Unisys Corporation
Post Office Box 500
Blue Bell, Philadelphia 19424-0001

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



February 8, 1991

U.S. Department Of Labor - OSHA
Director of Health Compliance
200 Constitution Ave.
Washington, DC 20210

Attention: Ms. Patricia Clark

Dear Ms. Clark;

I was referred to you by Dr. Barry in the Philadelphia office as the person who could help me with an acoustical standards problem.

Enclosed with this letter is a copy of parts of a standard which I believe is in violation of OSHA requirements. Please refer to Sections 57 and 59 of UL Standard 1459.

The first violation is, the standard allows sound levels in excess of 115 dBA and it allows it for and indeterminate amount of time. Furthermore, there is no consideration for the number of noise impulses between the levels of 120 and 140 dB. The UL 1459 definition for impulse is unclear and probably not correct since it defines the peak hold response as being "an acoustic response having a duration less than 50 microseconds". What about the treatment of longer impulses?

Apparently other people share my views. A copy of an advertisement is also enclosed which tries to promote the virtues of protection from acoustic emissions which are above OSHA rules.

Please consider the attached material and let me know if the requirements are in violation of OSHA rules and what should be done about the situation.

Sincerely,



David L. George, P.E.
Manager, Regulatory Requirements

Enclosures:



January 16, 1989

Telephone Equipment - UL 1459
Copyright 1985, 1989
Underwriters Laboratories Inc.

57. Acoustic Pressure Test

57.1 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 unit shall be tested in accordance with paragraphs 57.2 --- 57.8. Handsets, earphones, and headphones should be tested with the equipment they are intended to be used with, or equivalent equipment. Typical signals that should be considered are alerting and paging signals (on-hook operating state), and DTMF-tone (Dual Tone Multi Frequency tone) and other signals generated within the device and network signals that can cause high acoustic pressure output (off-hook operating state).

Revised paragraph 57.1 effective October 1, 1990

59. Peak Acoustic Pressure Test

59.1 The peak acoustic pressure emanating from the receiver earpiece shall not exceed 140 dB (relative to 20 micro-Pascals) 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 tho 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. For equipment no intended to be directly connected to the telecommunication network, such as equipment used with specialized PBX or Key systems and the like, the voltage surge is to be applied between the tip and ring terminals of the system. Response is to be measured using the appropriate coupler as specified in paragraphs 57.7 and 57.8. The sound pressure within the coupler in measured with a sound level meter set to use an unweighted "peak hold" response. "Peak hold" is defined as an acoustic response having a duration less than 50 microseconds.

Revised paragraph 59.1 effective October 1, 1990

REFERENCE: Advertisement

ACS Telephone Headsets

ACS Communications, Inc.



Standard Interpretations - Table of Contents Standard Interpretations - Table of Contents