Document LoogDx8Qz8mGMYBgQKnNYrmv3

Hygiene standards for asbestos 13 develop. Of the 10S workers exposed to less than 5 mp/ft', 82 had worked less than 5 years and only 4 had more than 10 years exposure. Moreover, it was a "point-in time" study; many of the ill were missing, the dead uncounted, and were not considered in the over-all evaluation of the limit. The British Hygiene Standards Committee finalised its views in November 1967 after studying the British data, and these views were immediately communicated to the ACGIH TLV committee. In May 1968 the ACGIH (Committee on Threshold Limits, 1968) proposed changes to its hygiene standard. The new asbestos limit, while taking into account the British views, had to be based on Ameri ran experience and considerations applicable to the American industrial scene. Recent evaluation of the health experience in asbestos plants in the U.S.A. had, nevertheless, indicated that the 5 mp/ft* limit was not sufficiently low to protect workers exposed for 30 years, a period rarely exceeded in America. In accordance with these findings, the 5 mp/ft* limit was made a ceiling value below which all concentrations should fluctuate. This corresponds to a time-weighted average concentration over a shift of 2 mp/ft*. Since the count by Irapinger procedure often consists primarily of extraneous particulates, an alternative fibre count was recommended, using the membrane filter method in which fibres greater than 5 p in length are counted as in Britain. On this basis, for a time-weighted 8-hr average limit by Impinger count of 2 mp/ft*, the corresponding limit based on the fibre count is 12 fibres/cm*. This limit is intended to reduce to an insignificant risk, the occurrence of asbestos disease among those exposed for 30 years to all forms of asbestos. The intended changes in American TLVs give two years' notice and objections to them should be conveyed to the TLV committee of the ACGIH. All objections are given the most serious and sympathetic consideration and users are strongly advised to take advantage of this if they have reason to question the proposed changes. The standards of the British Occupational Hygiene Society recommend that a person's accumulated exposure to chrysotile asbestos should not exceed 100 fibre ycars/cm*. It is probable that the risk of being affected to the extent of having early clinical signs of asbestosis will be less than 1 per cent if the conditions comply with these standards. It is believed that this is the first time a hygiene standard has been associated with such a specified degree of protection. The standards refer essentially to an average concentration during working hours over 3 months of 2 fibres/cm*. In an environment where this 3 monthly average just equals 2 fibres/cm*, the concentration within this period will sometimes be above this value and sometimes below. The maximum 8-hr average will thus be somewhat higher than 2 fibres/cm*. The proposed change in the American TLV is to a maxi mum 12 fibres/cm* 8-hr average, which if exceeded on a shift demonstrates noncompliance. Thus, there may be a rough degree of consistency between the hygiene standards from the two countries' organisations, so far as this is possible. The Factory Inspectorate in their work have often only a short time during a day to come to a judgment on conditions and are considering a development of this, applying a maxi mum for even shorter periods, of a few minutes, which if exceeded would indicate a probability that the Asbestos Regulations are not being complied with. There is a growing body of information on chrysotile dust and other asbestos dusts from many countries, and it is ^hoped that in future the views from different