OSHA recently updated the permissible exposure limits for respirable crystalline silica. Read on to learn more about the timeline to implement the new lower exposure limits and the processes that will improve employee health and minimize exposure.
Each day, about 295,000 general industry workers and two million construction workers are exposed to respirable crystalline silica. When crystalline silica particles are inhaled, they can cause irreversible health problems including silicosis, lung cancer and other respiratory diseases.
More than half of the Earth’s crust is comprised of silica and about 95 percent of rocks contain it. Silica is a naturally occurring mineral that is used to create many useful products. It is also used as filler in a variety of plastic materials, rubber and house paint, as well as sheet rock, batteries, optics, refractory materials, iron and steel. Common building materials, like concrete, cement, sandpaper, sandstone, granite and limestone, also contain silica. You can’t drill a well or dig a mine without encountering silica and it’s essential in the manufacture of fine china, glass and ceramics.
Silica is benign in its undisturbed state but becomes a health hazard when the solid crystals are reduced to tiny dust particles that can be easily inhaled. Whenever materials containing crystalline silica — masonry, brick, stone, concrete, glass — are sawn, drilled, chipped or crushed, silica dust is created and released. Silica sand is especially problematic because it is grainy and dusty, even in its natural state. Most particles are 100 times smaller than sand found on beaches.
Silica comes in two forms: crystalline and amorphous. In this article, we’ll focus on crystalline silica exposure as amorphous silica hasn’t been linked to adverse health effects.
In 1971, the Occupational Safety and Health Administration (OSHA) recognized respirable crystalline silica as a health hazard and established a permissible exposure limit (PEL) for it. The PEL was based on studies conducted in the 1960s. Technology advancements and demands for safer work conditions prompted OSHA to update their silica exposure rule to reflect these changes. OSHA published an updated final rule in March 2016. The rule requires employers to monitor their workplace to determine if workers are exposed to respirable crystalline silica and create a workplace exposure plan that outlines the procedures and controls that will be taken to prevent unsafe levels of exposure.
Workers in many industries can be exposed to respirable crystalline silica in the form of sand or when materials containing crystalline silica are ground, cut, milled or otherwise handled in a manner that causes silica dust to become airborne, including:
- Glass manufacturing
- Pottery products
- Structural clay products
- Concrete products
- Dental laboratories
- Paintings and coatings
- Jewelry production
- Refractory products
- Ready-mix concrete
- Cut stone and stone products
- Abrasive blasting in maritime, construction, and general industry
- Refractory furnace installation and repair
- Railroad transportation
- Oil and gas operations
Employers are required to identify workplace hazards and take all reasonable measures to eliminate or control those hazards so thry don’t injure employees. When workers may be exposed to respirable crystalline silica, employers in general industry and maritime must monitor the air in the workplace to determine the concentration of silica dust in the air that workers are breathing.
For general industry and maritime, OSHA has set an action level of 25 µg/m³ of respirable silica, averaged over an 8-hour day. If air monitoring results show that workers can be exposed to a time-weighted average (TWA) of 25 µg/m³ of silica dust, employers must create a written exposure control plan that describes the procedures that will be taken to minimize employee exposure. In addition to the basic planning requirements, if employees are exposed to more than a TWA of 50 µg/m³, employers must also provide respiratory and other forms of protection.
Because control measures to minimize airborne silica dust are well established in the construction industry, OSHA gives construction employers the choice to either conduct air monitoring to determine if their workers are exposed to the action level of 25 µg/m³, or use the control measures listed in Table 1, which lists common construction activities and the methods that must be used to control hazardous dust levels and minimize exposure.
Written Exposure Control Plans
Like most safety plans, employers may choose the methods, procedures, controls and products that they will use to prevent exposure and minimize risk. The facility’s written crystalline silica exposure control plan must identify all tasks that expose workers to silica hazards and detail the procedures that will be used to protect workers from overexposure.
Dust control methods, such as using water to control the amount of airborne dust that is generated, are an example of a procedure that may be implemented. Vacuums, local ventilation and isolating processes are additional examples of control methods that may be used.
Medical Evaluations and Surveillance
Overexposure to respirable crystalline silica can cause irreversible health effects. Routine medical surveillance can help to determine and identify the health effects associated with exposure to silica dusts so that employers can take appropriate actions.
Where employees are required to wear personal protective equipment, medical evaluations are necessary to determine an employee’s fitness to wear a respirator. Some health conditions, such as lung and heart diseases, may prevent a worker from wearing a respirator. Lung diseases can also make an employee more sensitive to respirable silica dust.
General industry and maritime employees who will be exposed at or above the action level for 30 or more days per year must receive chest x-rays and lung function tests every three years. Construction employees who are required to wear respirators for 30 or more days per year must also receive chest x-rays and lung function tests every three years.
For each employee, the employer receives only the physician’s recommendation for respirator use. Any other findings are given only to the employee. Employers must keep records of both silica exposure and medical examinations. OSHA doesn’t say in the rule how long you’re required to keep records, so it’s a good idea to keep all records forever to be safe.
Although it may seem like an easy solution to some employers, providing respirators should not be the only procedure listed in the exposure control plan. OSHA is clear about the use of engineering and other controls to control exposure and the use of respirators only as a last resort.
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Some of the controls that employers may use include:
- Limiting access to areas where exposure above the PEL could occur
- Using water to control dust levels
- Installing local ventilation or using vacuums to collect dust
- Restricting housekeeping practices
- Wetting dust before sweeping it up
- Using recommended water flow rates for tools with water controls
Health and Safety Blogsays:12/16/2016 at 2:28 am
This was a very good example and it set things straight and in a good understanding way.
Brittanysays:12/20/2016 at 9:03 am
Thank you for the feedback!
Erik Hallsays:12/21/2016 at 3:30 pm
Curious why there isn’t a manufacturing category in this list?
Brittanysays:12/22/2016 at 11:56 am
Great question, Erik! Manufacturing falls under the general industry category.
Mariesays:01/03/2017 at 9:28 am
Maybe I missed it, but the particle size of concern is PM10 and less, correct?
Karensays:01/10/2017 at 6:32 pm
In the final rule, OSHA did not include a particle size. Instead, they defined respirable crystalline silica as “quartz, cristobalite, and/or tridymite contained in airborne particles that are determined to be respirable by a sampling device designed to meet the characteristics for respirable-particle-size-selective samplers specified in the International Organization for Standardization (ISO) 7708:1995: Air Quality – Particle Size Fraction Definitions for Health-Related Sampling” [29 CFR 1910.1053(b)].
The ISO Standard provides definitions for “respirable fractions” of airborne particles as well as charts to help industrial hygienists determine inhalation ratios. In practice, most monitoring devices that would be used to sample respirable dust levels (such as respirable cyclones) are capable of detecting particles in the 1 to 10 micron range.
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