Page 2 of 4
Exploring Crystalline Silica Exposure
What do a dentist, a pottery shop owner, and a foundry worker have in common? They all work in environments that could expose them to respirable crystalline silica. In fact, OSHA estimates more than 2 million employees in the United States share this potential risk.
Exposure to respirable crystalline silica can cause silicosis, a form of lung cancer, as well as many other respiratory diseases. Because these risks are well documented, OSHA has established safety standards to help prevent health problems caused by silica.
Sources of Silica
Although crystalline silica is an inhalation hazard, it is very useful. Sand containing silica is used to make glass and ceramics. It’s also used to form molds in foundries and for sandblasting operations. Gravel and sand are used to make concrete for roads and other construction projects, and sand is an essential filter for water and sewage treatment.
Activities that involve drilling, grinding, cutting, crushing, or polishing materials such as stone, masonry, concrete, tile, rock, and other minerals can expose workers to respirable silica dust. It also can be present in floor sweeping compounds and loose absorbents that are used in many facilities. The industries most commonly at risk for silica exposure are mining, construction, foundries, manufacturing, and agriculture. However, exposure can also occur in industries such as jewelry making, dentistry, and porcelain finishing.
Silicosis
Silicosis is a preventable fibrotic lung disease that is caused by the inhalation of crystalline silica dust, causing the formation of scar tissue that reduces the lungs' ability to take in oxygen. There is no known cure for silicosis.
Documented cases of silicosis date as far back as ancient Greece. By 1800, the disease was commonly known as "grinders' asthma," "masons' disease," "potters' rot," and "stonemasons' disease." From 1968 to 1990, silicosis was listed as the underlying cause of death for 6,322 workers in the United States.
The effects of silica exposure can happen rapidly or may take 15-20 years to develop. The three most common forms of silicosis are chronic, acute, and accelerated. Chronic silicosis is the most common form and typically occurs after 15 to 20 years of low to moderate exposure. As the disease progresses, shortness of breath occurs; in later stages, fatigue, chest pain, and eventual respiratory failure often happen. Acute silicosis occurs within a few months or up to two years after exposure to very high concentrations of respirable silica dust. Accelerated silicosis can occur 5-10 years after exposure to respirable silica dust. With both of these latter forms of silicosis, symptoms include shortness of breath, weakness, and weight loss.
Other diseases that may be accelerated by and have been linked to crystalline silica exposure include tuberculosis, emphysema, chronic bronchitis, chronic obstructive pulmonary disease (COPD), and renal diseases.
Recognition of the Hazard
Crystalline silica dust can be extremely fine and, in fact, sometimes the particles may not even be visible. Where silica dust is generated, employers must test air quality and establish a safety program to prevent exposure when dust exceeds the permissible exposure limit (PEL).
OSHA and other workers’ safety organizations, including ASTM International, NIOSH, the National Institutes of Health, the American Lung Association, and the Centers for Disease Control and Prevention, recognize the hazards of crystalline silica and have established standards and guidance to help protect workers from its dangers. OSHA issued its first guidelines for workplaces with silica exposure in 1972, and in 1996 it initiated a silicosis national emphasis program. This program is aimed at significantly reducing exposure by providing ways to control the hazard, as well as providing outreach and compliance assistance to employers.
OSHA recently published a notice of proposed rulemaking that would amend its current regulations regarding crystalline silica exposure. The proposal seeks to lower the PEL of crystalline silica for workers in general industry, construction, shipyards, manufacturing, and other trades. It would also incorporate many common-sense work practice controls and other measures, such as air monitoring and respiratory protection programs, to help prevent or limit dust from entering workers' lungs.
Control Measures
Successful silica safety programs combine different types of control measures into a framework that identifies specific issues faced by workers and addresses how each hazard will be prevented. Many of the control measures that can be used to prevent or reduce silica exposure are common-sense approaches that are not overly expensive or difficult. In addition to guidance provided by safety groups, tool manufacturers and insurance carriers are traditionally good sources for suggesting engineering controls that increase the safety of different types of power tools.
Written Plans and Engineering Controls
Written plans are used to document the locations where respirable crystalline silica exposure may exist and to describe steps that will be taken to protect workers from these hazards. Plans should list how hazardous areas will be identified and how access to these areas will be restricted.
Engineering controls and respiratory protection protocols are important parts of safety plans. Because processes change and new control measures are always being discovered, plans must be reviewed at least annually and should be readily available for employees and inspectors to review.
OSHA has long held the belief that establishing work practices and engineering controls are preferential to relying solely on personal protective equipment when protecting workers. Work practices prescribe the way a worker performs a given task and in turn help to protect the worker as well as others who are in the area.
According to OSHA, "Engineering controls are reliable, provide consistent levels of protection to a large number of workers, can be monitored, allow for predictable performance levels, and can efficiently remove a toxic substance from the workplace. The effectiveness of engineering controls does not generally depend on human behavior to the same extent as personal protective equipment does, and the operation of equipment is not as vulnerable to human error as is personal protective equipment."
Engineering controls for silica vary slightly depending on the tools or processes used. They can be grouped into four categories: substitution, isolation, ventilation, and dust suppression. Substitution involves replacing silica with another less-hazardous material. Isolation is the process of creating a physical barrier around a process to contain and restrict dust from spreading throughout the workplace. Ventilation can be achieved either by supplying clean air to a worker performing a dusty task or by exhausting dust-filled air before it can be inhaled. Using water to wet down an area is the most common form of dust suppression; saws, grinders, drills, milling machinery, and other tools easily can be fitted with water-based dust suppression systems.
Respiratory Protection
Sometimes, engineering controls are not feasible or do not reduce crystalline silica exposure below the PEL. In these cases, respiratory protection can be used to supplement the safety program and bring exposure levels below the PEL.
OSHA currently enforces PELs for crystalline silica exposure in general industry, shipyards, and construction. Under the new proposal, PELs would be reduced from 100 μg/m3 in many industries to 50 μg/m3 for all industry sectors covered by the rule.
When respirators are used to lower exposure to respirable crystalline silica, employers must establish a written respiratory program that meets the requirements of 29 CFR 1910.134. The program must describe how respirators will be selected, fitted, and maintained, and it must describe how respirators are to be worn, cleaned, maintained, and replaced.
Medical Surveillance and Training
To help ensure that workers have not been exposed to excessive amounts of silica dust, the OSHA proposal would require employers to provide medical surveillance to all employees who are exposed to respirable crystalline silica above the PEL for 30 or more days per year. The examination would need to be provided at no cost and should include a physical examination, a chest x-ray, and a pulmonary function test. These evaluations would need to be performed at least every three years.
Because exposure to crystalline silica can cause lung cancer, employers are obligated under OSHA's Hazard Communication standard to ensure that workers understand this hazard and that they have access to labels, safety data sheets, and other information about it. After training, employees should be able to demonstrate how to use engineering controls and, when necessary, PPE to protect themselves from silica exposure.
Recordkeeping and Exposure Assessments
Recordkeeping establishes an employer's diligence in helping workers avoid hazards. Employee exposure measurements and sampling data are two types of records that should be kept. To help ensure that employees are aware of sampling and monitoring results, notifications must be provided to employees in writing or by posting the results in an accessible location in the facility, according to 29 CFR 1910.1053(d)(6)(i). If the PEL is exceeded, the notification must contain a description of the corrective actions the employer is taking to bring exposure below the PEL.
Understanding the hazards of respirable crystalline silica and developing written plans that document how engineering controls and PPE help to control these hazards increases safety and decreases the likelihood of workers developing silicosis or other respiratory diseases. As OSHA and other industry groups develop new regulations and guidance, facilities will be able to implement more advanced safety protocols to provide greater protection to workers and help prevent silica-related diseases.
This article originally appeared in the November 2013 issue of Occupational Health & Safety.