Worker exposure to crystalline silica dust often goes unchecked in construction because many managers and workers regard dust as “just part of the job.” Unfortunately, many workers don’t know that dust containing crystalline silica can be dangerous if too much is inhaled. Every year more than 250 workers in the U.S. die from exposure to silica dust and hundreds more become disabled from related diseases.

In response, OSHA has stepped up it efforts to reduce and eliminate the workplace incidence of silicosis from exposure to crystalline silica with the implementation of an agency-wide Special Emphasis Program (January 2008). Compliance officers have been directed to watch for and identify jobsites where silica exposures may exist so that they can be targeted for inspection. Additionally, some local and state ordinances require construction contractors to minimize dust to reduce both worker and public exposure. (See photo on the next page.)

Crystalline Silica Exposure

When the tiny silica dust particles are inhaled, they can embed themselves in the alveolar sacs and airways in the lungs, where oxygen and carbon dioxide gases are exchanged. Once embedded, the lungs cannot clear out the dust via the natural mechanisms of cilia and mucous. Overexposure can lead to silicosis, which is marked by inflammation and scarring in the form of nodules in the lungs. In the acute form, it is characterized by shortness of breath, fever and cyanosis (bluish skin). It can be deadly, especially if a person is exposed to very high levels for one to three years. However, in most cases the damage is a gradual decrease in lung function. Silicosis also increases a person’s susceptibility to lung infections and lung cancer. Based on epidemiological studies, crystalline silica has in fact been classified as a known human carcinogen. There is no known effective treatment for the disease.

To protect construction worker and public health, the Arizona DOT requires that the visible dust emitted from construction sites and vehicles not exceed 20 percent opacity; additional precautions, like water spraying, must be taken to prevent a dust plume or cloud from crossing a property line. (Photo provided by EPA.)

A naturally-occurring mineral, crystalline silica is a major component of sand, granite and other rock materials. Unfortunately, there are many construction tasks that generate dust containing crystalline silica, including, but not limited to grinding or cutting concrete, using a jackhammer to break rock or concrete, drilling rock, tunneling, cement mixing, sand blasting, using mobile excavation equipment (loaders, graders, dozers), etc. Even dry sweeping and other activities that generate a visible cloud of dust can create an exposure.

On jobsites where the potential exposure is high — such as where sand blasting or concrete grinding is performed — air samples should be taken and evaluated by an industrial hygienist. If the data indicates that the eight-hour time-weighted-average (TWA) established by OSHA’s permissible exposure level (PEL) of 10mg/m3 for respirable dust is exceeded, action must be taken. (Respirable dust refers to particles that are small enough to penetrate deep into the lungs.) The National Institute for Occupational Safety and Health (NIOSH) and the American Conference of Governmental Industrial Hygienists actually recommend a lower eight-hour threshold limit value (TLV) of 0.05mg/m3 because of the known dangers associated with inhaling crystalline silica.

Controlling the Exposure

To reduce the possibility of employees being exposed to dangerous levels of silica construction employers need to be proactive. The first step is to identify jobsites and job tasks that have the potential to create an exposure. The next step is to develop a site-specific safety and health plan to control or eliminate dust. Include engineering controls, PPE, safe work practices and administrative controls. If visible clouds of dust are observed while work is being performed, equipment is operating, trucks are rolling in and out of the site, etc., implement the plan. If sampling has not been completed, don’t take chances, take action.

Employee education is important to the success of any plan. Every employee who may be exposed to dust should understand the potential hazards and the plan to eliminate or control them. Each worker should know what he or she is expected to do. Some may not have to do anything except stay clear of the clouds of dust or away from areas where dust may be created while others may have to don dust masks and implement specific work practices.

Studies of actual construction jobsites have concluded that one way to lower silica dust levels is to use a water-spray control at a low flow rate. Water spray may not completely eliminate dust, but it has been proven that it can considerably reduce the amount of airborne dust that is generated. Wetting down an area where dust has settled before sweeping or removal will also keep the dust down. If you can’t find what you need commercially, make your own water-spray dust control. To find out how visit the NJ Laborers Web site — “How to Make Your Very Own Jackhammer Spray Dust Control” (www.njlaborers.org/health/pdfs/other/jackhammer.pdf) — or NIOSH (www.cdc.gov/niosh/docs/wp-solutions/2008-127/).

Although not as effective outdoors as wetting, commercially available dust collection systems can be set up to collect dust at the source. And, dry sweeping compounds are also available to control dust during cleanup.
To protect equipment operators and truck drivers, provide mobile equipment with enclosed positive-pressure cabs with air conditioning and a filtered air supply to isolate operators from the dust.

When retrofitting older cabs, it is better to locate heating and air conditioning vents as high in the cab as possible, rather than near the floor, to prevent the incoming air from stirring up the dust on the floor.

Use high-efficiency intake and recirculation filters to capture the dust. Cab doors and windows should seal properly, be in good condition and remain closed when working in dusty areas. Equipment and vehicles should be cleaned out regularly to prevent dust build-up. Use a vacuum cleaner with a high-efficiency filter to remove dust from vehicles and worker clothing; do not use compressed air.

In some situations respirators may be used, but it is important to note that they may not always provide adequate protection. NIOSH recommends the use of half-face particulate respirators with N95 or better filters for airborne exposures to crystalline silica at concentrations less than or equal to 0.5 mg/m3. OSHA also specifies the use of at
least an N95-rated mask or respirator (29 CFR 1910.134). (Paper dust masks do not meet the N95-rated requirement.) The N95 or N100 rating will be on the respirator or packaging. If respirators are required, a comprehensive respirator program including fit-testing must be instituted prior to use. The requirements for a comprehensive respirator program may be found in the OSHA Respiratory Protection Standard (29 CFR 1910.134).

Conclusion

The key to preventing silicosis is controlling dust that may contain crystalline silica. Construction managers and safety directors must understand when and where dust may be generated and plan ahead to control or eliminate it at the source. In situations where dust is a problem monitoring will be necessary to measure worker exposure to crystalline silica to determine the appropriate methods for controlling it. Control can be as simple as wetting the dust with a water hose before it becomes airborne or as detailed as a comprehensive respiratory protection plan.

For more information and training materials visit the NIOSH Web site at (www.cdc.gov/niosh/topics/silica/) or the OSHA Web site (www.osha.gov/dcsp/ote/trng-materials/silicosis/silicosis.html).

George Kennedy is NUCA Vice President of Safety.