Respirable Crystalline Silica Exposure

Created by the crushing, sawing, sanding, cutting, drilling, and grinding of stone, concrete, brick and mortar, small silica dust particles create a significant hazard for worker in a variety of industries. Crystalline silica particles with a diameter less than 10 μm are considered respirable, posing the most potential danger to employees. The extended inhalation of respirable silica particles can lead to these particles becoming embedded in lung tissue, significantly increasing the risk that workers develop silicosis, lung cancer, chronic obstructive pulmonary disease (COPD), and/or renal disease. With recent studies showing the harm of even low-level silica exposure, both the National Institutes of Health’s National Toxicology Program and the World Health Organization’s International Agency for Research on Cancer have classified crystalline silica as a known human carcinogen.

In recognition of these well-documented hazards, both OSHA and the European Union have recently announced new standard exposure limits, intended to provide better protection for workers. Previous exposure limits failed to reflect newly found correlations between low-level silica exposure and worker health and were inconsistent between industries and countries within the EU.

 

OSHA Silica Exposure Standards

OSHA published a final rule on respirable silica on March 25th, 2016, establishing two new standards: 29 CFR 1910.1053 and 29 CFR 1926.1153. Both standards establish a new 8-hour, weighted average exposure limit of 50 micrograms per cubic meter (μg/m³), and an action level of 25 μg/m³ for construction, general industry, and maritime workplaces. Compliance timelines vary by industry and should be verified to ensure worker safety and compliant working conditions. Workplace silica exposure is most commonly tested using either the OSHA 142 or NIOSH 7500 method. OSHA has verified that both testing methods are accurate and sensitive enough to measure samples for the new exposure limits.

 

EU-OSHA Silica Exposure Standards

EU-OSHA directive 2004/37/EC regarding worker exposure to carcinogens and mutagens in the workplace was recently amended on December 12th, 2017. This amendment lowered the binding limit value of respirable crystalline silica to an 8-hour, weighted average exposure limit of 0.1 mg/m3 (2004/37/EC, Annex III). The Directive enters into force as of January 16th, 2018 and the deadline for transposition into law by all EU member states is January 17th, 2020. While no testing methods are specified in this directive, both the OSHA 142 or NIOSH 7500 method can be used to test for compliance in the workplace.

 

Methods for Testing Crystalline Silica Exposure

Several methods can be used to determine the concentration of free crystalline silica within the workplace.

 

Method Description
OSHA 142 OSHA 142 is used to determine quartz and cristobalite concentration by x-ray diffraction (XRD).
NIOSH 7500 NIOSH 7500 is used to measure exposure to crystalline silica in the workplace and can be used to distinguish the concentration of all three polymorphs (quartz, cristobalite, and tridymite)

 

Products for Testing Crystalline Silica Exposure

 

Product # Description
AG4502550 Silver Membrane Filter, 0.45 µm, 25 mm
AP1003700 Absorbent Pad, 37 mm
M00003700 Empty Monitor Case, without ring
M000037A0 Empty 37 mm Monitor Cassette, with rings and plugs
PVC503700 PVC Membrane Filter 5.0 µm pore size, 37 mm diameter, hydrophobic PVC, white, plain
XX5000000 Flow-limiting Orifices, set of 5
XX6200004 Aerosol Adapter, Luer slip to 1/4 in.– 3/8 in. ID hose, stainless steel
XX6200006P Filter forceps, blunt end, stainless steel
XX1012500 Millipore Glass Microanalysis Filter Holder Kit
XX1012502 Millipore Glass Base and Stopper, 25 mm, Glass frit support
XX1012514 Millipore Glass Funnel, 15 mL, 25 mm, Borosilicate, Ground glass seal
XX2504700 6-place manifold, 47mm, stainless steel