Silicosis

Background

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, shortness of breath, and fatigue. It is a rare disease that develops decades after exposure to silica dust.

 

Risk factors
    • Crystalline silica dust, including quartz and cristobalite [1]

Workers in construction, mining, and some manufacturing industries are at an increased risk for developing silicosis due to occupational silica exposure. Silica is found naturally occurring in rocks, soil, and sand and is also found in construction materials including concrete and brick. Tasks such as drilling or grinding concrete, sandblasting, and stonecutting can lead to high levels of silica exposure.

Key Findings

The greatest risks of silicosis were observed among workers employed in the mining and primary metal processing sectors. Increased risk of silicosis was also observed among construction industry workers.

 

Mining 

Workers in mining and quarrying occupations may be exposed to silica during processes such as drilling, crushing, or blasting rock and stone.

    • Mining and quarrying including oil and gas occupations: 18.6 times the risk
      • Rock and soil-drilling occupations: 19.7 times the risk
      • Mining and quarrying: cutting, handling and loading occupations: 16.5 times the risk
Primary metal industries

Workers in iron and steel foundries are exposed to silica dust contained in foundry sand [2].

    • Iron foundries: 9.72 times the risk
    • Iron and steel mills: 1.40 times the risk
 
 
Metal processing and metal working occupations

Metal processing occupations involve operating furnaces, metal smelting, moulding, casting, rolling, and extruding, and related activities. Foundry workers have known exposure to silica in foundry sand. Metal workers are involved in metal shaping and forming, including forging, welding and flame cutting which can release silica into the work environment [3].

    • Metal processing and related occupations: 2.45 times the risk
    • Metal shaping and forming occupations: 1.41 times the risk
      • Metalworking-machine operators: 1.69 times the risk
      • Welding and flame cutting occupations: 1.26 times the risk
Construction

Workers can be exposed to silica dust during construction processes such as sandblasting, and breaking, grinding, cutting, drilling or sawing silica-containing materials including concrete, brick and mortar [4].

    • Construction industry overall: 1.20 times the risk
      • General contractors: 1.27 times the risk
        • Building construction: 1.48 times the risk
      • Special-trade contractors: 1.14 times the 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 27,816 —
2/3 Forestry, Fishing and
Trapping		 0 7,857 —
4 Mines, Quarries and
Oil Wells		 27 18,186 10.60 (6.98-16.10)
5 Manufacturing 74 565,737 1.13 (0.84-1.51)
6 Construction 22 175,679 1.20 (0.77-1.89)
7 Transportation, Communication
and Other Utilities		 7 165,949 0.36 (0.17-0.77)
8 Trade 18 357,388 0.55 (0.34-0.90)
9 Finance, Insurance and
Real Estate		 <5 19,415 —
10 Community, Business and
Personal Service		 37 484,003 0.85 (0.58-1.25)
11 Public Administration and
Defense		 12 157,933 0.63 (0.35-1.12)
         
* SIC: Standard Industrial Classification (1970)
† Hazard rate 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 26,772 —
21 Natural sciences, engineering
and mathematics		 <5 22,792 —
23 Social sciences and
related fields		 <5 24,940 —
25 Religion 0 113 —
27 Teaching and related <5 41,694 —
31 Medicine and health 12 108,760 1.46 (0.78-2.73)
33 Artistic, literary,
recreational and related		 0 12,730 —
41 Clerical and related 9 162,138 0.57 (0.29-1.13)
51 Sales 6 123,290 0.66 (0.29-1.50)
61 Service 31 298,291 1.08 (0.73-1.59)
71 Farming, horticultural
and animal husbandry		 <5 40,975 —
73 Fishing, hunting,
trapping and related		 0 463 —
75 Forestry and logging 0 7,729 —
77 Mining and quarrying,
including oil and gas field		 25 10,051 18.60 (12.00-28.60)
81 Processing
(mineral, metal, chemical)		 15 67,243 2.26 (1.33-3.84)
82 Processing
(food, wood, textile)		 8 81,535 1.01 (0.49-2.04)
83 Machining and related 25 161,901 1.34 (0.87-2.05)
85 Product fabricating,
assembling and repairing		 31 276,757 0.93 (0.63-1.38)
87 Construction trades 19 181,408 0.84 (0.52-1.36)
91 Transport equipment
operating		 6 143,841 0.34 (0.15-0.77)
93 Materials handling and related,
not elsewhere classified		 10 128,518 0.78 (0.41-1.48)
95 Other crafts and
equipment operating		 <5 23,409 —
99 Other occupations not elsewhere classified 15 180,651 0.83 (0.49-1.41)
         
* CCDO: Canadian Classification Dictionary of Occupations (1971)
† Hazard rate 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.

References

  1. Leung CC, Yu ITS, Chen W. Silicosis. Lancet. 2012;379:2008–18.
  2. Morteza MM, Hossein K, Amirhossein M, Naser H, Gholamhossein H, Hossein F. Designing, construction, assessment, and efficiency of local exhaust ventilation in controlling crystalline silica dust and particles, and formaldehyde in a foundry industry plant. Arh Hig Rada Toksikol. 2013;64(1):123–31.
  3. Canadian Centre for Occupational Health and Safety. Welding – Fumes And Gases: OSH Answers. (Updated 2016).
  4. US Occupational Safety and Health Administration. Metalworking Fluids: Safety and Health Best Practices Manual.