Silicosis

Background

What is silicosis?

Silicosis is scarring and thickening of the lungs caused by inhalation of silica dust. Silicosis reduces lung capacity and can cause symptoms such as chronic cough.

Risk factors
    • Crystalline silica dust, including quartz and cristobalite

Workers in construction, mining, and manufacturing industries are at an increased risk for developing silicosis due to occupational silica exposure. Tasks such as drilling or grinding concrete, sandblasting, and stonecutting can lead to high levels of exposure.

Key Findings

The greatest risks of silicosis were observed among workers employed in the mining and processing sectors.

Mining 

Based on the ODSS results, the mining, quarrying, and oil well industry is at a significantly increased risk of silicosis. Within the mining industry, the gold quartz and uranium mining sectors have particularly high risks of silicosis. By occupation, the highest risk of silicosis is observed among mining foremen, who tend to be longstanding workers within the mining industry and likely incur significant exposure to silica dust over their careers. Drilling and blasting occupations also showed high risks of silicosis.

    • Mining foremen: 28 times the risk
    • Gold quartz mines: 22 times the risk
    • Uranium mines: 15 times the risk
    • Drilling and blasting occupations: 15 times the risk
    • Iron foundry workers: 7.5 times the risk
Mineral, metal, clay, and chemical processing occupations

These processing occupations are at an increased risk of silicosis. This work involves cutting and handling materials such as stone, clay, and brick, which would expose workers to high levels of crystalline silica.

    • Processing occupations (mineral, metal, clay, chemical): 2 times the risk
 
Machining

Machining and related occupations include welding and flamecutting and metalworking-machine operators. This work involves handling and shaping metals, wood, clay, glass and other raw materials. Tasks include buffing, grinding, and polishing these materials, which leads to dusty work environments and potential exposure to crystalline silica.

    • Metalworking-machine operators: 1.6 times the risk
    • Welding and flamecutting: 1.4 times the risk
Construction

Based on the ODSS results, the workers in the construction industry and construction occupations are not at increased risks of silicosis. The handling and use of raw materials in construction occupations could lead to dusty work environments and possible exposure to silica dust. However, no increased risk of silicosis was seen among these groups.

    • Excavation grading, paving and related occupations: No increased risk
    • Other construction trades occupations: No increased risk
    • General contractors: No increased risk
Relative Risk by Industry and Occupation

Figure 1. Risk of silicosis diagnosis among workers employed in each industry group relative to all others, Occupational Disease Surveillance System (ODSS), 1999-2016

The hazard ratio is an estimate of the average time to diagnosis among workers in each industry/occupation group divided by that in all others during the study period. Hazard ratios above 1.00 indicate a greater risk of disease in a given group compared to all others. Estimates are adjusted for birth year and sex. The width of the 95% Confidence Interval (CI) is based on the number of cases in each group (more cases narrows the interval).

 

Figure 2. Risk of silicosis diagnosis among workers employed in each occupation group relative to all others, Occupational Disease Surveillance System (ODSS), 1999-2016 

The hazard ratio is an estimate of the average time to diagnosis among workers in each industry/occupation group divided by that in all others during the study period. Hazard ratios above 1.00 indicate a greater risk of disease in a given group compared to all others. Estimates are adjusted for birth year and sex. The width of the 95% Confidence Interval (CI) is based on the number of cases in each group (more cases narrows the interval).

Table of Results

Table 1. Surveillance of Silicosis: Number of cases, workers employed, and hazard ratios in each industry (SIC)

SIC Code * Industry Group Number of cases Number of workers employed Hazard Ratio (95% CI) †
1 Agriculture <5 27,780
2/3 Forestry, Fishing and Trapping 0 7,846
4 Mines, Quarries and Oil Wells 29 18,105 9.65 (6.47, 14.4)
5 Manufacturing 101 565,241 1.25 (0.97, 1.62)
6 Construction 28 175,557 1.20 (0.80, 1.8)
7 Transportation, Communication and Other Utilities 9 165,863 0.37 (0.19, 0.71)
8 Trade 24 357,119 0.54 (0.35, 0.82)
9 Finance, Insurance and Real Estate <5 19,374
10 Community, Business and Personal Service 53 483,653 0.91 (0.66, 1.25)
11 Public Administration and Defense 17 157,830 0.71 (0.44, 1.17)
         
* SIC: Standard Industrial Classification (1970)    
† Hazard ratio in each group relative to all others    

 


Table 2. Surveillance of Silicosis: Number of cases, workers employed, and hazard ratios in each occupation (CCDO) group

CCDO Code * Occupation Group Number of cases Number of workers employed Hazard Ratio (95% CI) †
11 Managerial, administrative and related <5 26,751
21 Natural sciences, engineering and mathematics <5 22,780
23 Social sciences and related fields <5 24,933
25 Religion 0 110
27 Teaching and related 5 41,679 0.97 (0.40, 2.38)
31 Medicine and health 15 108,721 1.21 (0.70, 2.11)
33 Artistic, literary, recreational and related 0 12,723
41 Clerical and related 12 162,055 0.56 (0.31, 1.01)
51 Sales 8 123,185 0.63 (0.31, 1.28)
61 Service 37 297,987 0.96 (0.68, 1.37)
71 Farming, horticultural and animal husbandry <5 40,929
73 Fishing, hunting, trapping and related 0 463
75 Forestry and logging 0 7,724
77 Mining and quarrying, including oil and gas field 26 10,005 16.10 (10.60, 24.40)
81 Processing (mineral, metal, chemical) 19 67,193 2.18 (1.36, 3.49)
82 Processing (food, wood, textile) 8 81,486 0.74 (0.37, 1.50)
83 Machining and related 35 161,762 1.49 (1.04, 2.15)
85 Product fabricating, assembling and repairing 42 276,583 0.98 (0.70, 1.37)
87 Construction trades 22 181,269 0.78 (0.50, 1.22)
91 Transport equipment operating 10 143,762 0.45 (0.24, 0.85)
93 Materials handling and related, not elsewhere classified 15 128,454 0.88 (0.52, 1.48)
95 Other crafts and equipment operating 5 23,380 1.34 (0.55, 3.24)
99 Other occupations not elsewhere classified 23 180,530 0.98 (0.64, 1.52)
         
* CCDO: Canadian Classification Dictionary of Occupations (1971)  
† Hazard ratio in each group relative to all others    

Please note that ODSS results shown here may differ from those previously published or presented. This may occur due to changes in case definitions, methodological approaches, and the ongoing nature of the surveillance cohort.