The case for lowering OSHA’s silica permissible exposure limits
OSHA has proposed to reduce the occupational health exposure to crystalline silica dust due to the evidence of risk of lung cancer, silicosis, chronic obstructive pulmonary disease, and kidney disease.
The current OSHA permissible exposure limit (PEL) is based on a formula based on the percent of crystalline silica in sets of bulk samples rather than the percent crystalline silica in each individual air sample. OSHA and MSHA collected and reviewed occupational health data of crystalline silica dust exposures (1974–1994) by inspecting various manufacture, construction, and maritime industries. The data showed elevated occupational exposures above equivalent permissible exposure limits of 100 micrograms/m3 (µg/m3) for general industry and a 250 µg/m3 for an 8-hour time weighted average (TWA).
MSHA exposures were elevated but not as significant as the OSHA sample results.
With technological innovations and greater awareness of hazard, the prevalence of silicosis was reduced but the occupational exposures limits remain the same.
A current longitudinal study of the entire OSHA database on crystalline silica dust exposures (1984–2013) supports changing the OSHA PEL to the NIOSH recommended exposure limit (REL) of 50 µg/m3 with an action limit (AL) to the ACGIH threshold limit value (TLV) of 25 µg/m3.
The current study also identifies the industrial divisions and major groups where crystalline silica dust exposures were found during the OSHA inspections, supporting the need for further industrial hygiene investigation of the contaminant source(s) and the provisions for training and education of workers, medical surveillance, initial periodic air monitoring, hierarchy selection and use of engineering/administrative controls and/or respirators, personal protective clothing and equipment, and more robust collaboration on the hazards and controls with all stakeholders to further reduce the risk of occupational illness and disease.
Health hazards associated with exposure to crystalline silica-containing dusts arise from the inhalation of the respirable dust fraction, which is comprised of particles sufficiently small to reach the deep lung. The respirable fraction is broadly defined as particles having a diameter of 10 μm or less (IARC, 1997). It is this portion of crystalline silica-containing dust that is of most concern to OSHA and MSHA. The occupational diseases associated with inhalation of respirable crystalline silica include: lung cancer, silicosis and other non-malignant respiratory diseases such as; pulmonary tuberculosis; chronic bronchitis with airflow limitation, and emphysema (both more commonly referred to as “chronic obstructive pulmonary disease,” or COPD); and several extra-pulmonary diseases (renal and immunologic) and cancer (lung and other).
These occupational diseases, either alone or in combination, are life-altering and debilitating disorders that annually affect thousands of workers across the United States. Many of these diseases are also life-threatening. The preponderance of evidence for the adverse health effects associated with inhalation of crystalline silica, as described extensively in the scientific literature consists of studies of exposed workers. However, many animal and in vitro studies have also been conducted in an effort to elucidate the toxicological mechanisms by which crystalline silica increases the risks of adverse health effects.
OSHA’s current permissible exposure limits (PELs) for crystalline silica polymorphic forms were adopted from national consensus standards prior to1971 and they have not been updated since that time. Based on weight of evidence from current epidemiological, toxicological, and medical information in the peer-reviewed literature, the OSHA PELs do not adequately protect workers from occupational illness or disease. The OSHA exposure limits appear outdated, inconsistent, and hard to understand when compared to other published occupational health guidelines such as the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs) and NIOSH RELs.
The National Toxicology Program (NTP), within the International Agency for Research on Cancer (IARC), and NIOSH have identified all forms of crystalline silica as a human carcinogen while the ACGIH considers polymorphs of crystalline silica – quartz and cristobalite as suspect human carcinogens. In a proposed rule to protect workers, OSHA acknowledged that inhalation of very small (respirable) crystalline silica particles puts workers at risk for silicosis, lung cancer, chronic obstructive pulmonary disease (COPD), and kidney disease.
OSHA estimates that 2.2 million US workers are exposed to crystalline silica dust, of which 1.85 million of these workers are in the construction industry. This data translates into exposures for approximately 1 to 2 workers per every 100 workers. Other industries with well documented crystalline silica dust exposures in the OSHA IMIS databased include manufacture, agriculture, forestry, some mining, wholesale and retail trades, transportation, electric and gas, real estate, public services and service trades.
Collectively, the OSHA cohort of air sampling results clearly indicate a pattern to determine if the proposed OSHA PEL (e.g., NIOSH REL) should be further considered or modified based on historical perspectives. In our opinion, the ACGIH TLV can be used as an action level and the NIOSH REL can be used as the maximum exposure guideline for all industry based on weight of evidence, toxicity, and distribution pattern of the air sample results for the polymorphs of quartz. Most industries could achieve regulatory compliance with current technology and the hierarchy of controls. Additionally, the analysis of the air sample results should discern the difference between various polymorphs rather than considering all crystalline silica dust similarly. The breakdown in sample analysis may help better understanding of the toxicity for each of these silica polymorphs.
Changes in management practices will be necessary to help protect the at-risk workforce through the construct of enforceable policy, written programs, and development of standard operating procedures for the effective use of engineering and/or administrative controls along with the use of respirators, personal protective clothing and equipment, periodic medical surveillance, initial and periodic risk assessments to monitor ambient environmental conditions, training and educating the workforce and supervisors, and collaborating with industry and trade associations, physicians and other healthcare professionals, universities, unions and labor groups, and other affiliated stakeholders regarding the relative risk of illness and disease and the overall danger crystalline silica dust exposure. The current OSHA PEL for general industry is approximately 0.10 mg/m3 and for construction and shipyards, it is about 0.25 mg/m3 as an 8-hour TWA.
Based on past OSHA initiatives and directives, many industries, business, organizations, labor groups, and workers (direct hires and contract support) will awaken to the occupational health hazard of being exposed to crystalline silica dust. The impact could affect profitability, productivity, and human performance. Industry and other stakeholders will be relied upon to develop a national campaign and awareness program, construct sustainable communications for public and social media, develop new innovative control technologies, plan new management strategies to reduce operating cost through medical and healthcare, enforce the use of engineering and/or administrative controls, solicit insurance incentives, collaborate on regulatory compliance requirements, and other concerns which affect business operation, brand, image, and reputation. Workers should be onboard and engaged to understand the significance of the occupational health hazards, risk of respiratory illness and disease, and they should be encouraged to report unhealthful exposures associated with various operations, processes, or work tasks which may expose them to elevated levels of crystalline silica dust. Together everyone can make a difference in preventing the occupational hazard and reducing the exposure risk.
The business case and value can be demonstrated by the additional cost saving, which can be achieved by reducing hidden and expensive indirect costs that reduces human performance and production output and increases the risk of human error, absenteeism, lost work time and restricted days away from work, reduced morale, and other psychosocial work stress. An effective collaborative effort is necessary to prevent workers from contracting the debilitating occupational disease or illness from crystalline silica dust exposure.Independent studies and metrics are needed to evaluate industry strategic plans by developing realistic whole goals and objectives that clearly demonstrate the economics of cost effectiveness and cost savings to all industries and business while protecting affected workers’ health.