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2016SummerShotcreteEMag

Technical Tip OSHA’s New Crystalline Silica Rule– Potential Impact on Shotcrete Operations By Charles S. Hanskat Background The Occupational Safety and Health Administration (OSHA) recently issued a final rule dealing with worker exposure to crystalline silica. The rule represents years of effort by OSHA to develop a standard that is intended to help protect over 2 million construction workers from respirable crystalline silica. This is one of the biggest rules OSHA has developed, and it is addressed to two different workplace environments: construction and general industry/maritime operations. Our field shotcrete operations fall into the construction category. This is a very comprehensive standard addressing not only permissible levels of exposure but also exposure monitoring, medical surveillance, and housekeeping. Crystalline silica has been a known health hazard for decades. Significant levels of exposure can lead to silicosis, lung cancer, other respiratory diseases, and kidney disease. How is one exposed to respirable crystalline silica? Common jobsite concrete work including cutting, drilling, jackhammering, chipping, grinding, or sand blasting of concrete present the highest potential for exposure above the safe limits established in the rule. The new rule was published June 23, 2016, and requires compliance of the rule by June 23, 2017, except for the requirements for laboratory evaluation of exposure samples that will begin 1 year later. The rule deals with all exposures of respirable crystalline silica, except those environments that have proven exposure less than an action level of 25 μg/m3 over an 8-hour time-weighted average (TWA). Many contend the 25 μg/m3 level is at or below the limit that can be measured accurately and consistently with current technology. So what about silica fume, a common supplemental cementitious material widely used in shotcrete? ACI defines silica fume in CT-13, ACI Concrete Terminology, as “very fine noncrystalline silica produced in electric arc furnaces as a byproduct of the production of elemental silicon or alloys containing silicon.” The key here is that silica fume is a noncrystalline material. However, most producers of silica fume do note that trace amounts of crystalline silica—less than 0.5% of the overall silica fume material—are present in their materials. Thus, as OSHA significantly reduces the permissible exposure limits (PEL) in construction environments from the previous 250 μg/m3 over an 8-hour TWA to 50 μg/m3, there may be concern that even trace amounts of crystalline silica in silica fume may impact our shotcrete crew’s exposures. All of our shotcrete mixtures use sand as an aggregate, so handling of quantities of sand in site-batching operations or from rebound may also produce small amounts of crystalline silica that add to the worker exposure. Also, many of our shotcrete projects involve repair of existing concrete, so surface preparation techniques may produce crystalline silica. Two Alternative Approaches for Compliance Provided in Rule Work Tasks Covered by Table 1: The new rule offers two ways to be in compliance. The first method, and the one OSHA expects most contractors to use, provides a table (refer to Table 1) that predefines specific equipment and associated exposure conditions, along with control and respiratory protection measures required. If the work environment is covered in Table 1 and the specified engineering and work practice control methods are met, along with the required respiratory protection, there 30 Shotcrete • Summer 2016


2016SummerShotcreteEMag
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