Silica and Dust Exposure

Not all dust is equal. The dust that hurts you most is often too fine to see. Respirable crystalline silica is made when you cut, grind, drill or crush stone, concrete, brick, mortar, tile or sand. It goes deep into your lungs and stays there. Damage builds up over years and cannot be reversed. The good news is that water and vacuum controls work very well, and they cost much less than a ruined pair of lungs.

What You Will Be Able to Do

• Name the materials and tasks that make respirable silica dust.
• Explain the OSHA limit and what the action level means.
• Choose a control for common tasks, and use it correctly.
• Clean up without putting dust back into the air.
• Recognize other dust hazards and know when to stop work.

What Silica Does to Your Body

Crystalline silica is a basic mineral in the earth's crust. Quartz is the most common form. The harmful particles are at least 100 times smaller than ordinary sand, and you can breathe them in without seeing a thing. Exposure can cause:

• Silicosis, an incurable scarring of the lungs that can disable or kill.
• Lung cancer.
• Chronic obstructive pulmonary disease (COPD).
• Kidney disease.

Silicosis often takes years to appear. It can also come on quickly, within months to a few years, after very heavy exposure. Workers who cut and finish engineered stone countertops have developed severe disease at young ages, because that material can be more than 90% silica.

Where You Find It

Dust spreads, so workers near the task are exposed too, even if they never touch the tool.

The OSHA Rules

There are two silica standards: 29 CFR 1926.1153 for construction, and 29 CFR 1910.1053 for general industry and maritime.

• Permissible Exposure Limit (PEL): 50 micrograms of respirable crystalline silica per cubic meter of air, as an 8-hour average.
• Action level: 25 micrograms per cubic meter, as an 8-hour average. Reaching this level triggers further steps under the general industry rule, such as more air monitoring and medical surveillance for those exposed 30 or more days a year.

A microgram is a millionth of a gram, so the limit is a tiny amount of dust. You cannot judge it by eye, and clean-looking air can still be over the limit.

Employers must have a written exposure control plan. Construction employers also need a competent person to inspect jobs and equipment and act on problems. A competent person is someone who can identify silica hazards and has the authority to fix them.

Medical surveillance is offered at no cost in construction when you must wear a respirator for silica 30 or more days a year. It includes a chest X-ray and a breathing test.

Table 1 for Construction

The construction standard has a list called Table 1, which matches common tasks with the exact controls to use. If the employer follows Table 1 fully, it does not need to measure the air for that task. Otherwise, it must measure exposure and keep it below the PEL.

Worked example: A crew uses a handheld power saw on concrete. Table 1 says to use a saw with a built-in water delivery system that continuously feeds the blade.

APF is the assigned protection factor, and a half-mask respirator with the right filter has an APF of 10. Without the water feed running, the crew is not following Table 1, and the respirator column no longer applies.

Controls That Work

Use these in order. Engineering controls come before respirators.

1. Change the material or method where you can, such as using a low-silica abrasive instead of sand for blasting, or making cuts off site in a controlled shop.
2. Use water. Wet cutting and wet drilling keep dust out of the air. Keep the water flowing, and manage the slurry.
3. Use local exhaust. Tool shrouds connected to a HEPA vacuum capture dust at the source. A HEPA filter traps at least 99.97% of very fine particles. Check the vacuum's airflow and filter, and empty it the way the maker says.
4. Use enclosures. Closed, filtered cabs on heavy equipment keep dust away from the operator.
5. Separate people. Work at a distance from others, schedule dusty work when fewer people are around, and put up barriers.
6. Use a respirator where the plan calls for one.

Warning: A dry saw with no dust control can put you over the limit within minutes, even outdoors. If the water line is empty or the shroud is missing, stop and fix it before you cut.

Cleaning Up

• Do not dry sweep or dry brush where it can raise dust, unless wet sweeping, HEPA vacuuming and other methods are not feasible.
• Do not use compressed air to blow dust off surfaces or clothing, unless it is used with a ventilation system that captures the dust, or there is no other way.
• Use a HEPA vacuum or wet methods instead.
• Wash your hands and face before you eat, and leave dusty work clothes at work if you can, so dust does not reach your home.

Other Dusts to Know

Warning: If you might disturb old pipe insulation, floor tile, roofing or paint, and you do not know what it is, stop and ask. Asbestos and lead need testing and special procedures. Sanding or cutting them first and asking later is how people get exposed.

Common Mistakes

Check Your Understanding

1. Your crew cuts block with a wet saw outdoors for 2 hours a shift, with the water on. Do you need a respirator under the Table 1 entry for that tool?

Check the Table 1 row for your specific saw. For a handheld saw with continuous water, no respirator is needed outdoors for 4 hours or less. Stationary masonry saws and other tools have their own rows.

2. The water feed fails halfway through a day of cutting concrete. The foreman says to keep going since you are outside. What should happen?

Stop and fix the water. Without it, the Table 1 controls are not being followed and exposure can go over the limit quickly.

3. A fine gray dust covers the floor after a drilling job. How do you clean it up?

Use a HEPA vacuum or wet methods. Do not dry sweep or use compressed air.

4. You are about to grind an old floor and see black tile under the carpet. What do you do?

Stop and ask. Older tile and mastic may contain asbestos. It must be tested before anyone disturbs it.

Key Takeaways

• Respirable silica comes from cutting or crushing concrete, stone, brick, tile and sand.
• The damage is permanent. It can cause silicosis, lung cancer, COPD and kidney disease.
• The limit is 50 micrograms per cubic meter, and the action level is 25.
• Water and HEPA vacuum controls come first. Respirators come after.
• Never dry sweep or blow dust around with compressed air if a safer way exists.
• Stop work if you might disturb asbestos or lead.