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Government Affairs

Construction workers are exposed to a wide variety of occupational hazards each year and existing silica regulations have not been revised in quite some time. Accordingly, due to pressure from labor organizations and increased concerns about overexposure and the resulting health problems in the construction industry, The Department of Labor has been forced to do research and feasibility studies to determine how to develop a new formula for measuring exposure limits of respirable dust. Although a proposal is not imminent, I thought it might be useful to give our readers a general overview of some of the issues associated with new silica standards.

Silicosis is a permanent, disabling and sometimes fatal lung disease caused by breathing dust containing extremely fine particles of crystalline silica. When concrete, masonry and rock are made into a fine dust — through abrasive blasting of concrete, demolition of concrete and masonry structures, or chipping, hammering, drilling, sawing, and grinding of concrete or masonry — and suspended in the air, breathing in these fine particles can produce lung damage.

The U.S. Department of Labor reports that more than one million U.S. workers, in all industries, are exposed to crystalline silica each year. More than 250 American workers die with silicosis each year, yet only a very small percentage of those fatalities are attributable to occupational exposures in the construction industry.

While there is no cure for silicosis, it is 100 percent preventable if employers, workers and health professionals work together to reduce exposures. Working in any dusty environment where crystalline silica is present generally can increase a person's chances of getting silicosis.

As one might imagine, screening and monitoring for silicosis can be very expensive. More importantly, although exposure to silica can lead to other diseases such as bronchitis, tuberculosis and lung cancer, contractors must be leery of whether or not those illnesses can definitely be linked to on-the-job performance. Smoking and predisposition to allergies or bronchial problems are just a few of the many real complex problems with reducing exposure limits to silica for those in the masonry industry.

Crystalline silica is regulated by a number of OSHA standards, all of which employers should understand. In order to comply with established OSHA permissible exposure limits, the employer must first implement engineering or administrative controls whenever possible. Administrative control methods include job rotation to minimize exposure and protect workers. Also, when sawing concrete or masonry, workers can use saws that provide water to the blade. Second, during rock drilling, use water through the drain stem to reduce the amount of dust in the air and, third, use dust collection systems where possible.

OSHA established Permissible Exposure Limits (PELs) for many substances, including airborne crystalline silica. PEL is the maximum amount of a contaminant in the air to which workers may be exposed over a given time period. (The OSHA PEL for crystalline silica in general industry is listed in the Code of Federal Regulations, 29 CFR 1910.1000, "Air Contaminants," under Table Z-3, "Mineral Dusts." )

This is a time-weighted average amount that cannot be legally exceeded for an eight-hour shift during a 40-hour week. OSHA has published general industry PELs for three different forms of crystalline silica. Cristobalite and tridymite are forms of crystalline silica, less abundant than quartz, that have lower PELs than quartz. OSHA PELs for respirable crystalline silica, expressed in milligrams of respirable dust per cubic meter of air (mg/m3) are as follows:

Permissible Exposure Limits
Silica, Crystalline


Cristobalite: Use 1/2 the value calculated from the above mass formula for quartz.

Tridymite: Use 1/2 the value calculated from the above mass formula for quartz.

The chart accompanying this article shows a sample calculation for a mixture of crystalline silica.

One can easily see why so many in the construction industry believe this formula is complicated and should be revised and simplified. Yet a federal appeals court ruled recently 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 of the General Industry Standard for failing to protect its workers against respirable dust containing crystalline silica. 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. 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 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.

What sort of impact will this court decision have on OSHA's revisions to the existing silica exposure standard? It is difficult to say but it should give us all at MCAA a greater sense of urgency to be an active and prudent participant in the development of a new silica exposure standard to ensure that it is not overly broad and correspondingly difficult to administer and costly to enforce.

Marian Marshall was named director of the MCAA Government Affairs office July 1, 2002. She has nearly 25 years experience working with the Congress and Executive branches of the U.S. government and oversees all MCAA legislative, regulatory and political action activities.

Sample Calculation for a
mixture of crystalline silica: 1

Calculation of the TWA from the sampling and analytical data:
Step No. 1:
Calculate the percentage of quartz, cristobalite, and tridymite in the respirable particulate collected

Percentage = (weight of quartz in Sample A) + (weight of quartz in sample B) x (100) Total weight of respirable particulate collected

= 0.052(0.855 mg) + 0.048(0.619 mg) x (100)/(0.855 mg + 0.619 mg)

= 0.044 mg + 0.03 mg x (100)/1.474 mg = 0.074 mg x (100)/1.474 mg = 0.05(100) = 5%

Percentage = (weight of cristobalite in sample A) + (weight of Cristobalite in sample b) x (100)/Total weight of respirable particulate collected

= 0.023(0.855 mg) + 0.017(0.619 mg) x (100)/1.474 mg

= 0.02 mg + 0.011 mg x (100)/1.474 mg

= 0.031 mg x (100)/1.474 mg = 0.021(100) = 2.1% = 2%

Tridymite: None Detected = 0%

Step No. 2:
Calculate the PEL for the mixture (use the formula in the OSHA Technical manual Appendix I-1.5)

PELmixture = 10 mg/m3/[ % quartz + 2(% cristobalite) + 2(% tridymite) + 2]

= 10 mg/m3/[5.0 + 2(2.0) + 2(0) +2]

= 10/11 = 0.91 mg/m3

Step No. 3:
Calculate the employee's exposure to respirable dust

Exposure = (sample weight A + Sample weight B)/Total volume of air sampled

= (0.855 mg + 0.619 mg)/ 731 liters (1 m3/1000 liters)

= 2.0 mg/m3

Step No. 4:
Adjust (where necessary) for sampling period less than 8-hours. Assume a zero exposure time for the sampling period remaining.

Adjusted Exposure = (2.0 mg/m3)(430 minutes) + 0(50 minutes)/480 minutes

= 2.0 mg/m3 (430 minutes)/ 480 minutes = 1.8 mg/m3

Step No. 5:
Calculate the Severity of the exposure:

Severity = Adjusted Exposure/PELmixture

= (1.8 mg/m3)/(0.91 mg/m3) = 2.0

If the result from Step 5 is greater than 1.0 than an overexposure to the mixture of crystalline silica exists.

1. Occupational Safety and Health Administration Technical Manual: OSHA Instruction TED 1.15.
References Related to Appendix A



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