Silica dust: when you have to sample, and how

This page explains what the rules and common practice call for. Every site is different, and what a survey or a filing needs at your facility is something we work out with you after we see it.

OSHA has two silica standards. If you run a plant or a shop, you fall under the one that gets written about less.

One standard covers construction. The other covers general industry, which takes in foundries, mineral processors, glass and ceramics plants, countertop shops and most other fixed workplaces. The two are not the same, and the gap between them matters.

Silica is found in sand, stone and concrete. Cutting, grinding or blasting these materials produces a very fine dust that workers can inhale, which OSHA calls respirable crystalline silica.

The difference that costs employers money

The construction standard has a shortcut, known as Table 1. The general industry standard does not.

Table 1 lists common construction tasks and, for each one, the dust controls and respiratory protection to use. A construction employer who fully and properly implements those controls on a listed task is following that path and does not have to measure worker exposure for that task.

The general industry standard has nothing like it: no shorter table, no alternate table, and no task list at all.

What general industry gets instead is called the performance option. You may rely on air monitoring results, on objective data, or on a combination of the two, provided the data is good enough to show what your workers are actually breathing. This path rests on data, not on a task list, so you cannot skip the exposure assessment by following a recipe.

Installing the Table 1 controls does not satisfy your obligation under the general industry standard. You still have to assess exposure.

Exposure limits

• Permissible exposure limit (PEL): 50 micrograms per cubic meter of air (µg/m³), as an 8-hour time-weighted average (TWA).
• Action level: 25 µg/m³, as an 8-hour TWA. At or above the action level, you have to continue monitoring.
• Silica has no short-term exposure limit (STEL) and no ceiling limit.

Where plants and shops find silica dust

• Foundries: sand handling, shakeout, core making and finishing
• Glass manufacturing
• Ceramics and pottery
• Brick and refractory work
• Cutting and fabricating engineered and natural stone
• Abrasive blasting with silica-containing media
• Mineral processing and crushing
• Asphalt and concrete products
• Cement
• Dental laboratories
• Handling sand for hydraulic fracturing

In a foundry, shakeout and finishing usually have the highest exposures in the building. They are often sampled as a single exposure group together with pouring, and they should not be.

How we sample for it

Appendix A is where the standard lists the approved analytical methods. Your sampling plan should name which of those methods the laboratory will use.

Sample volume is a detail people often overlook. The laboratory has to be able to measure amounts well below 25 µg/m³, which requires enough air to pass through the cyclone. That means a full shift at the correct flow rate.

A short sample can come back as “none detected” only because too little dust reached the filter. That result is worse than useless, because it looks like a pass when it is not one.

What your results require you to do

The silica standard sets out these steps:

• Initial monitoring below the action level: you may stop monitoring. You do not need a second round to confirm an initial result.
• At or above the action level, but at or below the PEL: repeat the monitoring within 6 months.
• Above the PEL: repeat the monitoring within 3 months.
• A later result (not your initial one) below the action level: continue monitoring every 6 months. You may stop once two consecutive results, taken 7 or more days apart, are both below the action level.
• Notify your workers within 15 working days, in writing. If a result is above the PEL, the notice must describe what you are doing to correct it.

Keep this distinction between initial and later monitoring in mind, because it matters for every substance you monitor. → See how often monitoring is required, by substance