Workers Health & Safety Centre

Research on silica exposure controls finds PPE comes at a cost

Emile Tompa
Research estimating cancers averted and intervention costs of two silica control measures offers an important new perspective on the control of occupational cancers.

Among the compelling findings, researchers concluded that personal protective equipment (PPE) is not the most cost-effective method of protecting workers from silica exposures, calling into question the common practice of providing PPE to workers exposed to hazardous materials.

The research findings were presented at a recent plenary by lead investigator, Emile Tompa (see photo), health and labour economist and senior scientist at the Institute for Work & Health.

Silica—widespread exposure, significant disease burden

Silica is a common mineral and a component of soil, sand and rocks (granite and quartzite). CAREX Canada estimates 380,000 Canadian workers are exposed to crystalline silica, of these 237,000 have high exposure levels. Workers in the construction sector have the greatest source of exposure but other exposures can occur in mining and manufacturing, oil and gas extraction and transportation.

Workers are commonly exposed when products containing silica are disturbed by grinding, cutting, drilling, or chipping which creates respirable silica dust. Crystalline silica dust is classified as a human carcinogen by the International Agency for Research on Cancer. Silica also causes silicosis and is linked to chronic obstructive pulmonary disorder, rheumatoid arthritis and pulmonary tuberculosis.

The 2017 Burden of Occupational Cancer in Ontario report estimates 142,000 Ontario workers are exposed to crystalline silica, causing almost 200 lung cancer cases every year, half of which are in the construction sector.

Research objectives and key findings

The research team led by Tompa, also included researchers from the Occupational Cancer Research Centre, the University of British Columbia and Ryerson University. The research was funded by the Ontario Ministry of Labour Research Opportunities Program.

Researchers conducted an impact analysis to assess the benefits and averted lung cancers associated with two exposure methods—wet methods which involve spraying down work surfaces to minimize dust and PPE, in this case the use of half-face respirators. They further set out to determine when the benefits equaled or exceeded the intervention costs or, break-even point.

Researchers considered costs (direct health care, productivity and health-related quality of life) at a societal level. They also estimated the number of future workers exposed to silica dust spanning 30 years and the future silica-related lung cancers under current practices. They then calculated the numbers of cancers prevented with each of the two methods, monetized the benefits and determined a break-even point.

Some of the key research highlights are:
  • Due to disease latency, it can take many years for intervention costs to break even with the costs of averted cancers
  • It was assumed all exposed workers could use PPE (100 per cent) vs wet method (62 per cent)
  • Baseline compliance levels were assumed to be higher for PPE than wet methods
  • Costs for PPE were approximately $400/person compared to $200/person for wet method
  • Break-even point for the wet method occurred four years earlier than PPE method
  • Occupations where wet methods could be used and which employ the greatest number of construction workers, include construction trades helpers and labourers, heavy equipment operators, bricklayers and concrete finishers.

Researchers note, their cost estimates are somewhat conservative because the research did not account for other diseases that might also be prevented by these control methods, nor did it consider other controls such as local ventilation, nor the effectiveness of a combination of controls.

Support for prevention action now

The burden of illness associated with occupational silica exposure is significant. The average lifetime cost of a lung cancer case is estimated to be $1,002,175. With continued growth in the construction sector, researchers estimate the number of silica exposed workers will increase.

This latest research evidence highlights the societal cost of occupational cancer and something more difficult to measure—the value of prevention.

Prevention advocates have long argued both regulatory reform and effective workplace measures are needed to protect worker health. Since 1983 silica, and several other carcinogens, have been regulated as Designated Substances under Ontario’s Occupational Health and Safety Act and yet, construction projects remain exempt, something many would like to see end.

These Regulations adopt the hierarchy of controls, understanding the most effective and protective hazard controls rely upon PPE as the last, not the first, line of defense.

Primary prevention looks to eliminate or reduce worker exposure altogether. With changes in 2017 construction worksites are now covered under O. Reg. 833 (Control of Exposure to Biological or Chemical Agents) which sets out occupational exposure limits (OEL) for a host of substances, including silica. Many however, also continue to call on Ontario’s Ministry of Labour to lower the OEL for crystalline silica to 0.025 mg/m3—the level currently recommended by the American Conference of Governmental Industrial Hygienists and adopted by six other Canadian provinces.
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