Respirable crystalline silica is the exposure I am asked about most often and the one most often assessed by guesswork. A contractor tells me the crew wets the saw, so there is no exposure. That is a control, not a measurement, and the two are not interchangeable.
The numbers
Under 8 CCR section 5204 the permissible exposure limit is 50 micrograms per cubic metre as an eight-hour time-weighted average, with an action level of 25 micrograms per cubic metre. The action level is where monitoring obligations and medical surveillance considerations begin, which is why an employer who assumes the PEL is the only number that matters tends to be surprised.
What a sampling day looks like
Personal sampling, not area sampling, is what characterises an employee’s exposure. A calibrated pump is worn on the belt with the sampling head in the breathing zone, at the collar. The cyclone separates the respirable fraction. The pump runs across the full shift, or long enough to represent it, and is calibrated before and after; a pump that has drifted outside tolerance invalidates the sample.
What matters as much as the pump is the field record: task, duration, tool, blade or bit, material, water on or off, ventilation, respirator worn, wind, enclosure, how many other operations ran nearby. A laboratory result without that record tells you a number and nothing about what produced it, and it cannot be used to defend or to change anything.
Samples go to an accredited laboratory. Results come back with a limit of detection and a limit of quantitation, and a result reported as below the limit of detection is not the same as zero — it is a statement about the method at that sample volume.
Engineered stone is treated differently in California
California’s high-exposure trigger tasks on artificial stone containing more than 0.1 per cent crystalline silica by weight carry requirements that have no federal counterpart: wet methods regardless of what the monitoring shows, powered air-purifying respirators at an assigned protection factor of 1000 or higher with HEPA or N100, R100 or P100 filtration, a prohibition on compressed air, dry sweeping and employee rotation as a means of reducing exposure, and a medical examination within 30 days of assignment and every three years after.
The point of the rule is that for those tasks, monitoring cannot buy an employer out of the controls.
Why the data has to be yours
Objective data from a trade association or an equipment maker can inform a hazard assessment, but it describes someone else’s saw, someone else’s material and someone else’s ventilation. When a citation turns on exposure, the argument is won with sampling from that crew, on that material, doing that task — and lost with a brochure.
Michael Karl McNeil, registered industrial hygiene professional and registered environmental professional.
Michael Karl McNeil 