§ 43.43. Special protection against dust.
(a) Special definitions. The following words and terms, when used in this section, have the following meanings, unless the context clearly indicates otherwise:
(1) Rock drilling—Drilling, cutting, chipping, channeling, broaching or crushing by means of machinery or hand hammers.
(2) Silica-bearing rock—Any rock formation, natural or synthetic, containing as a component part, free silicon dioxide. This shall include the following classes:
(i) Class I—Any rock formation of substantially uniform geological character having free silicon dioxide as a component part which is known from geological studies or otherwise may be shown by the applicant to the satisfaction of the Department to run uniformly less than 10% by weight, of the rock formation.
(ii) Class II—All rock formations having free silicon dioxide as a componenet part, 10% or more by weight, and all other formation, natural and synthetic, having a variable and unpredictable content of free silicon dioxide of more than 10%.
(3) Injurious silica dust concentration—Dust particles less than ten microns in size produced from drilling silica-bearing rock which is in excess of the following values as determined by an approved dust count method:
(i) Class I—100 million particles per cubic foot of air.
(ii) Class II—Ten million particles per cubic foot of air.
(b) Drilling. All drilling in silica-bearing rock shall be so executed that there is no dissemination of injurious silica dust concentrations in the breathing zone of the worker.
(c) Ventilation. In order that the dust concentration shall be kept within specifications, only wet drilling or local collection employing suction or exhaust, with the necessary ventilation is permitted. Ventilation shall consist of general ventilation, exhaust systems or a combination of the two to produce the desired results.
(d) Vision. During any and all excavations and construction operations in the tunnel, the atmospheric conditions at the point of the operations shall be maintained so that there is clear vision at all times in order that work may be conducted safely.
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