Ruling Upholds OSHA Method of Calculating Silica Exposure

A federal appeals court ruled April 13 that OSHA's method of calculating actual worker exposure to respirable silica is reasonable.

The precedent setting decision stems from a case in Ohio where OSHA cited a casting company for violating section 1910.100(c) of the General Industry Standard for failing to protect its workers against respirable dust-containing crystalline quartz silica.

Overexposure to crystalline silica can cause silicosis, which results in permanent lung damage and disability. Silica sand is a commonly used abrasive in blast cleaning. It is an expendable yet inexpensive abrasive, which is known for its good cutting power and ability to create a surface profile or anchor pattern for good primer coat adhesion.

Although the use of silica sand abrasive is banned in many countries, it is allowed in the U.S. and remains one of the most widely used abrasive for blast cleaning. Many facility owners however, prohibit the use of silica sand when blast cleaning is done at their facilities. Many abrasive suppliers refuse to sell it. OSHA is currently working on crystalline silica standard for the construction industry.

At the heart of the company's contest of the citation was its belief that OSHA incorrectly calculated employee exposure. The company claimed that its method, as opposed to OSHA's, was the correct one to use to calculate exposure.

Table Z-3 of the cited OSHA standard states that a worker's exposure to respirable silica in any 8-hour work shift during a 40 hour work week, shall not exceed the 8-hour time weighted average (TWA) limit given for that substance. The standard contains a mathematical formula for calculating the permissible exposure limit (PEL) for various "mineral dusts" including crystalline quartz silica.

PEL is the maximum amount of a contaminant in the air to which workers may be exposed over a given time period.

OSHA calculates actual silica exposure by dividing the total weight of the entire respirable dust sample (silica and non-silica), by the volume of air flowing through the sampling pump.

The cited company argued that by using the total weight of the dust sample instead of just the weight of the respirable silica, OSHA was penalizing the company for exposing its workers to all respirable dust, regardless of silica content.

The company's sample showed that workers were not exposed above the PEL while OSHA's sample said they were. The cited company used its calculating method to justify not providing its workers with respiratory protection.

In supporting OSHA's calculation method, the court ruled that respirable silica and nuisance dust are interrelated. Workers exposed to silica dust, the court stated, were usually exposed to a mixture of silica and nuisance dust.

Source: U.S. Court of Appeals for the Sixth Circuit, Ohio Cast Products, Inc., v. Occupational Safety and Health Review Commission. Docket No. 99-4398/4409, April 13, 2001.