Document re4gMbREL34q6Oam3mnNvoz4a

Industrial Noise Threshold limit values for physical agents for 1969 These threshold limit values refer to levels of physical agents and represent conditions under which it is believed that nearly all workers may be repeatedly exposed day after day without adverse effect Because of wide variations m individual susceptibility, ex posure of an occasional individual at, or even below, the threshold limit may not prevent annoyance, aggravation of a pre-existing con dition, or physiological damage Threshold limit values refer to levels of exposure for a 8-hour workday for a 40-hour work week Exceptions are those limits which are given a ceiling value (C) They should be used as guides in the control of health hazards and should not be used as fine lines between safe and dangerous levels of exposures These threshold limits are based on the best available information from industrial experience, from experimental human and animal studies, and when possible, from a combination of the three These limits are intended for use in the practice of industrial hygiene and should be interpreted and applied only by a person trained in this discipline They are not in tended for use, or for modification for use, (a) in the evaluation or control of the levels of physical agents in the community, (b) as proof or disproof of an existing physical dis ability, or (c) for adoption by countries whose working conditions differ from those in the USA These values are reviewed annually by the Committee on Threshold Limits for Physical Agents for revisions or additions, as further information becomes available Ceiling value There are some physical agents which produce physiological response from short intense exposure and whose threshold limit is more appropriately based on this particular response Physical agents with this type of response are best controlled by a ceiling "C" limit which is a maximum level of exposure which should not be ex ceeded Notice of intent At the beginning of each year, proposed actions of the Committee for the forthcoming year are issued in the form of a "Notice of Intent " This notice provides not only an opportunity for comment, but solicits suggestions of physical agents to be added to the list The suggestions should be accompanied by substantiating evidence As Legislative code. Although the Con ference does not consider the Threshold Limit Values appropriate matter for adoption in legislative codes and regulations, it recog nizes that the values may be so used If so used the intent of the concepts contained in the Preface should be maintained and provi sions should be made to keep the list current Reprint permission This publication may be reprinted provided that written permission is obtained from the Secretary-Treasurer of the Conference and that this Preface be pub lished m its entirety along with the Threshold Limit Values Threshold limit values tor noise for 1969 These threshold limit values refer to sound pressure levels that represent conditions under which it is believed that nearly all workers may be repeatedly exposed without adverse effect on their ability to hear and understand normal speech The medical profession has defined hearing impairment as an average hearing threshold level in ex cess of 15 decibels (ASI Z24 12 --1952) at 500, 1000, and 2000 Hz, and the limits which are given have been established to prevent a hearing loss in excess of this value These values should be used as guides in the con trol of noise exposure and, due to individual susceptibility, should not be regarded as fine lines between safe and dangerous levels Continuous or intermittent. The sound level shall be determined by a sound level '"Guides for the Evaluation of Heanng Impair ment" Transactions of the American Academy of Ophthalmology and Otolaryngology, pp 167-8, March-Apnl, 1959 "Guides to the Evaluation of the Permanent Im pairment, Ear, Nose, Throat and Related Struc tures " Journal of the American Medical Associa tion, 197 489 August 1961 1534