What’s the Risk?
A worker’s chance of becoming ill from exposure to silica dust depends on the tasks performed, the amount of dust they are exposed to, and the frequency of the exposures. Each exposure to silica adds into the total load of silica in the lungs – in other words, each exposure adds to the lung damage.
Health professionals express the total silica dose one person accumulates over time as “mg/m3 years," usually calculated as an average exposure each year in mg/m3 multiplied by the number of years with that exposure, or by an estimated average for each year. As the total dose increases, so does the likelihood, or the risk, for developing silicosis, lung cancer, or chronic obstructive pulmonary disease (COPD). Some workers become ill after many years of low exposure levels, while other workers who perform less frequent but high exposure tasks can become ill with a lower cumulative exposure. Why? Because a high exposure to silica dust overwhelms the lungs’ defenses and most of the dust settles deep into the lungs where it does the most damage.
Researchers have developed estimates of the total dose likely to cause disease. For example:
- Among granite workers in the U.S. the rate of death from silicosis doubled at a cumulative exposure of less than 1 mg/m3.
- A recent study of pottery workers found high rates of silicosis, up to 20%, among workers with an average exposure of 0.2 mg/m3 over many years.
- The likelihood of getting lung cancer from silica exposure follows a similar pattern, with a significant risk at levels around 0.2 mg/m3 over many years, or higher exposures in a shorter period of time.
- There is less information available to estimate the risk for COPD, but there is documentation showing that about 25% of cement masons, bricklayers, and plasterers have COPD after many years of work in the trade.
These very general estimates do not take into account individual susceptibility or other exposures at work that add onto the injury caused by silica and lead to disease at an earlier age.
It is important to remember that repeated exposures to silica add up to a total dose that can cause serious lung disease. The kinds of exposures we see in high exposure tasks, such as sandblasting and tuckpointing, over time can give a worker enough exposure to put him or her at serious risk for a silica-related illness.
To learn more about the risk….
- A Case-Control Study of Airways Obstruction Among Construction Workers; John Dement, PhD; Laura Welch, MD; Knut Ringen, Dr.PH; Patricia Quinn, BA; Anna Chen, BS and Scott Haas, MJ (2015)
- Update: Silicosis Mortality - United States, 1999-2013; Jacek M. Mazurek, MD; Patricia L. Schleiff, MS; John M. Wood, MS; Scott A. Hendricks, MS; Ainsley Weston, PhD (2015)
- Silica: A Lung Carcinogen; Kyle Steenland, PhD; Elizabeth Ward, PhD (2014)
- Exposure-Response Analysis and Risk Assessment for Lung Cancer in Relationship to Silica Exposure: A 44-Year Cohort Study of 34,018 Workers; Yuewei Liu; Kyle Steenland; Yi Rong; Eva Hnizdo; Xiji Huang; Hai Zhang; Tingming Shi; Yi Sun; Tangchun Wu; Weihong Chen (2013)
- Determinants of Respirable Crystalline Silica Exposure Among Stoneworkers Involved in Stone Restoration Work; Catherine B. Healy, Marie A. Coggins, Martie Van Tongeren, Laura Mac Calman and Padraic McGowan (2013)
- Long-Term Exposure to Silica Dust and Risk of Total and Cause-Specific Mortality in Chinese Workers: A Cohort Study; Chen W, Liu Y, Wang H, Hnizdo E, Sun Y, et al. (2012)
- Chronic obstructive pulmonary disease and longitudinal changes in pulmonary function due to occupational exposure to respirable quartz; Mohner, M., Kersten, N., Gellissen, J. (2012)
- Chronic Obstructive Pulmonary Disease and Occupational Exposure to Silica; Rushton, L.