Many things like bees and rattlesnakes, if left alone, won’t cause you any harm. Once agitated, however, they can be deadly. It’s the same with silica. Crystalline silica is found inalmost all rock, sand and soil in the earth’s crust. Left alone, silica quartz (rock) is harmless. Once “agitated” or airborne, however, silica dust can be deadly.

So if you grind, cut, stone, batch, core, drill, sweep or sandblast any material that came from the earth, like cement and concrete, you could be supplying silica with its ticket to fly through the air as a very fine dust. Once silica dust is airborne, it is called RCS, or respirable crystalline silica, and it is a microscopic but unforgiving killer (see the sidebar “Inhaled Silica Dust Can Lead to Death”).

For precast workers, it is important to know that cement dust is comprised mostly of calcium and silica. If there’s even a remote chance you could breathe in silica dust, you must wear a NIOSH1-approved respirator. Simple, right? Unfortunately, proper respirator use is not simple.

Respirators in the real world

In the real world, using a respirator in a precast concrete plant can sometimes be viewed as a nuisance. Either it’s too hot to wear, it’s difficult to talk through or it just gets in the way. Another reason workers often neglect the respirator is that silica dust gives no clear warning – the danger isn’t always obvious. As such, workers may grab a disposable dust mask in lieu of strapping on the appropriate respirator.

NIOSH publishes the recommended exposure limit for RCS as 0.05 mg/m3 as an average over a 10-hour day during a 40-hour workweek. But measuring particulates this small is the business of industrial hygienists and has little relevance for the average worker. Recent studies show that workers have a significant risk of developing chronic silicosis if they are exposed to RCS over a working lifetime, even at the NIOSH recommended exposure limit.2

So what does all this mean? It means that if you work with materials that contain silica and you work in an area where silica can become airborne – due to concrete cutting, grinding, coring, stoning, cement mixing and sweeping, or sandblasting – you need to wear a respirator.

Some straightforward facts about respirators and silica dust

The following list is not meant to be inclusive of all respirator-related guidelines. Refer to OSHA Regulation (Standard 29CFR) 910.134, “Respiratory Protection,” for complete requirements of a respirator program.

1. Precast plants need the services of an industrial hygienist consultant to conduct air sampling (some insurance companies provide this service free) and to provide management with the reading’s results.

2. From the air sampling results, the specific contaminant and a rough estimate of its airborne concentration at the plant can be identified. This will help determine whether workers are within the permissible exposure limit for silica dust.

3. Wherever respirators are used, someone at the precast plant must serve as the program administrator. This person needs to understand the health hazard, the type of respirator needed, and how to use the respirator safely and effectively. He or she must maintain written operating procedures and records (medical evaluations, fit-testing and training) for respirators.

4. Respirator user instructions must be understood by anyone who wears a respirator.

5. With very limited exception, all respirator users must be medically evaluated as to whether they can safely wear a respirator, and the plant must keep records of the evaluations, fit tests and training. Workers with asthma or other diseases may not be able to safely wear a negative-pressure respirator.

6. The seal between the worker’s face and the respirator is critical; facial hair, glasses, or even skin and facial features can greatly reduce the effectiveness of a respirator. Workers must be fit-tested annually and perform a negative or positive pressure seal check each time a respirator is used.

7. Respirators must be inspected prior to use, and worn or missing parts/spent cartridges must be replaced. A minimum daily respirator inspection and a weekly cleaning with isopropyl alcohol should be required. Employees should be responsible for their own equipment.

8. Rule-of-thumb: If dust containing silica is visible in the air, it is almost always over the permissible limit.

9. Never wear a disposable dust mask in place of a NIOSH-certified respirator for possible silica dust exposure. The dust mask typically has only one plastic band; the respirator will have two bands, the NIOSH approval and a rating.

10. Wear a NIOSH-certified N95 respirator to minimize inhalation of silica dust and a P95 respirator when spraying form oils.

1 NIOSH is the National Institute for Occupational Safety and Health

2 NIOSH Hazard Review “Health Effects of Occupational Exposure to Respirable Crystalline Silica,” 2002.

3 See NIOSH pamphlet, “Construction Workers: It’s Not Just Dust! … Prevent Silicosis” at

Inhaled Silica Dust Can Lead to Death

Inhaled silica dust can cause silicosis, a disease from which scar tissue forms in the lungs and reduces the ability to breathe. It is a progressive, debilitating disease that can lead to death. There is no cure. Symptoms of silicosis include shortness of breath, coughing, fatigue and chest pains.

Silicosis occurs when microscopic particles of silica become embedded in the lungs. With continued exposure, lungs become scarred and the affected worker has difficulty getting enough oxygen when breathing normally. Silicosis often remains undetected in its early stages.3


Here’s a test on the dangers of silica dust and the proper use of respirators that you can use during your regularly scheduled safety or staff meeting. All are true/false statements and the answers are below.

1. Sandblasting always requires the use of a respirator.

2. Precast concrete does not contain silica.

3. Silicosis is a minor ailment that can be readily treated.

4. Acute silicosis may develop even after very short periods of high exposure to silica dust.

5. As a worker, your exposure to silica dust will depend on the wind, where you stand and whether you use water to control dust.

6. You must wear a respirator while cutting wet concrete.

7. An exposure assessment should be done to determine the proper respirator to use for a given silica exposure.

8. Engineering controls such as wet sawing or ventilation/vacuum systems should be used before relying on respirators.


1. True.

2. False. Silica is found in all concrete products and in bricks.

3. False. Silicosis is a debilitating lung disease with no known cure.

4. True.

5. True. Exposure may vary significantly from day to day, depending on site conditions.

6. False. According to Industrial Hygiene in Construction, if wet concrete cutting is done correctly, you should not need a respirator.

7. True. The proper type of respirator used depends on the exposure level and the type of work being done (sawing or abrasive blasting).

8. True. OSHA requires that all feasible engineering controls be used before relying on respirators.