Sixth Sense Safety Solutions Gives Presentation to Holmes Safety Association Annual Meeting – Silica

Respirable Crystalline Silica (RCS) and MSHA Proposed Rules

I had the privilege of speaking at the Great Lakes District Council (Holmes Safety Association) Annual Meeting on October 5th in Gaylord, MI. Thank you Mark Zinser, for inviting me to speak. What a great opportunity to talk again with a variety of people from the metal/non-metal mining and construction industry, see some old friends from Michigan Tech University’s Mine Safety Program (Ron Gradowski, CMSP, Jake Drenth, Marisa Roerig), meet Mine Safety and Health Administration (MSHA) staff from Lansing, MI and Duluth, MN,  and other folks who attended.

Occupational exposures to respirable crystalline silica may cause various adverse health effects, and MSHA is proposing a new rule that it believes would better protect miners from health effects that can stem from to respirable crystalline silica. Many types of mining involve the collection and processing of materials that can contain crystalline silica in varying concentrations, and mining processes can alter the mined product to create dusts of a size that can penetrate deeply into the lungs and cause adverse health effects. The type of particles of concern are referred to as “respirable,” and so the proposed standard pertains to better controlling exposures to “respirable crystalline silica” or RCS.

The rule for what MSHA categorizes as metal/non-metal mining, is a bit different than the proposal for coal mining. Our discussions were about protecting workers in metal/non-metal mining, and potential impacts to companies.

MSHA’s proposed rule would both decrease the allowed amount of exposures to RCS, and also require mine operators and companies working in mine sites where miners’ exposures exceed certain levels, to take particular actions to decrease exposures to further protect miners. The new rule would set the permissible exposure limit of respirable crystalline silica at 50 micrograms per cubic meter of air (µg/m3) for a full shift exposure, calculated as an 8-hour time weighted average, for all miners. It would also set an “action level” of 25 µg/m3. Note that the Occupational Safety and Health Administration (OSHA), which regulates occupational safety and health in “general industry,” “construction” and other industries, had updated “its” RCS rules which became effective starting in 2017.

Talking about proposed regulations is not usually an exciting or entertaining thing, but we discussed what RCS is, where it can be found, why exposures to it can be of concern, some methods of control, an overview of the MSHA proposed RCS rule, some suggestions for how to frame the proposed rule, some basic information about exposure assessment and engineering controls, potential impacts to companies, and possible preparatory actions. 

There are some definite differences between the MSHA proposed rule and the OSHA rules, and nuances to some of the MSHA proposed rule. For example, where OSHA would permit the use of N95 type filtration for negative pressure air purifying respirators for conditions where a respirator was deemed necessary and where the level of exposure was appropriate (so that the facepiece type provides the required level of protection), the MSHA proposal would require at least a 100-type filter (such as N100), where exposure assessments would deem the use of filters (with particular facepiece type) appropriate. It will be interesting to see what MSHA does with the comments it received during the public comment period for the proposed rule, which ended (after an extension) on September 11th, 2023.


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