The concentration of silica in the air workers breathe exceeded occupational health criteria at all 11 hydraulic fracturing sites tested by the National Institute for Occupational Safety and Health, the American Industrial Hygiene Association announced July 31.
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In some instances, the samples exceeded OSHA's PEL by a factor of 10 or more.
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In some instances, the samples exceeded OSHA's PEL by a factor of 10 or more.
