Construction workers are exposed to cancer-causing silica dust when they do jobs such as concrete work, abrasive blasting, demolition, excavation and tunnel construction, to name a few. According to an estimate by the Occupational Cancer Research Centre, silica dust is responsible for 570 cases of lung cancer in Canada a year, with the majority of these—about 56 per cent—diagnosed in workers from the construction industry.
Worksites can use different prevention methods to reduce silica dust exposure. These include:
- the wet method, which involves applying water to materials before the dust is generated to prevent it from getting into the air—a method applicable to activities such as demolishing concrete surfaces, unloading gravel and excavating;
- local exhaust ventilation, which captures silica dust close to the source before it reaches the breathing zone of a worker—a method applicable to activities such as drilling, stone/concrete cutting and grinding; and
- personal protective equipment (PPE) in the form of air-purifying respirators, used by workers in areas with silica dust in the air—a method applicable to most activities and occupations in the construction sector.
To help construction workplaces decide which of these three methods—or combination thereof—would be the most cost-beneficial, a team of researchers led by the Institute for Work & Health (IWH) conducted an economic evaluation of the options in Ontario’s construction sector.
The team found a combination of all three methods can avert the highest number of lung cancer cases (107 cases per year). However, the most cost-beneficial approach is the wet method used in combination with local exhaust ventilation. This pairing can deliver $1.40 in benefits for each dollar spent—a benefit-to-cost ratio of 1.4.
The level of exposure is an important variable to consider in selecting the most cost-beneficial intervention, says Dr. Amir Mofidi, lead author of the open access article about this study, published in BMC Public Health in February 2020 (doi: 10.1186/s12889-020-8307-7).
With low levels of silica dust—i.e. levels at or below 0.025 milligrams per cubic metre—the team’s recommendation would be the wet method combined with local exhaust ventilation, he explains. With a higher level of exposure, the combined use of all three methods is expected to result in a higher net benefit.
Mofidi notes, however, that due to long latency periods, the benefits realized as a result of averted cases of lung cancer are only seen many years after the interventions are first introduced. He adds that the team is working on another paper that offers an estimated timeline to realize maximum net benefits.
Drawing on past research
The study used an innovative method that drew on past studies on the epidemiology and economic burden of occupational cancer, and on workplace interventions to reduce silica dust exposure. For estimates of silica dust exposure in Ontario’s construction sector, the team relied on work by the Occupational Cancer Research Centre and CAREX Canada. For the cost-benefit analysis, the team used a method developed by IWH Senior Scientist and study lead Dr. Emile Tompa. In recent years, Tompa has used this method to estimate the societal costs of occupational cancers caused by asbestos in Canada, and the societal costs of work injuries and diseases in European Union countries.
Here’s how the different methods compare.
The highest number of lung cancer cases can be averted when workplaces use a combination of all three methods—for a total reduction of 107 cases per year. This method is the most expensive. It would cost $138.6 million per year to cover all Ontario construction workers exposed to silica dust. The benefit-to-cost ratio is 1.3, meaning that for every dollar spent, a benefit of $1.30 is gained.
Using the wet method in combination with local exhaust ventilation can avert 95 cases. This pairing of methods would cost $57.6 million a year to implement, resulting in a benefit-to-cost ratio of 2.9.
The results showed the use of PPE on its own can deliver similar outcomes as the use of the wet method in combination with local exhaust ventilation, in terms of averted cases (96 cases). However, PPE would have higher implementation costs, about $81.1 million, resulting in a lower benefit-to-cost ratio of 2.2.
The wet method on its own can avert 55 cases at a cost of $42.0 million—a benefit-to-cost ratio of 2.2. Local exhaust ventilation on its own has a benefit-to-cost ratio of 4.4 at a cost of $15.5 million, though it averts only 40 cases. Since these methods on their own can protect only a proportion of workers, the team considered the costs and benefits of each in combination with PPE.
The findings of this study suggest that employers in the construction sector might consider several factors when selecting a control method, says Tompa. These are:
- the coverage of the control method, since some methods are applicable only to certain types of construction activities;
- the level of silica dust exposure, since the most cost-beneficial control method is not the same for different levels of silica dust exposure (for estimates of the costs and benefits of several intervention methods at different levels of silica dust exposure, see the open access journal article); and
- the availability of resources for prevention, since the control method that can avert the highest number of lung cancer cases is not necessarily the method that results in the highest benefit-to-cost ratio.