Silica

Crystalline silica is found in a variety of occupations and industries, including mining, quarrying, crushing and processing, road construction, cement finishing and demolition. Despite engineering controls and respiratory protection, over-exposure remains common.

Chronic inhalation of airborne crystalline silica can cause simple silicosis and obstructive airway disease. Symptom questionnaires, standard chest x-rays, and lung function tests are used to screen for these diseases. High-resolution chest CT scans can detect silicosis at an earlier stage, but cost, availability, and radiation exposure have limited their use to confirmatory (diagnostic) testing.
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When a worker’s cumulative (life-time) exposure to silica exceeds 1-2 mg/m3-years, screening for these diseases becomes feasible. Key challenges include:
* accurate estimation of a worker’s historical exposure to silica
* risk communication and informed consent
* quality and interpretation of chest x-rays
* quality and reliability of lung function testing
* interpretation of longitudinal lung function testing.
* determining when exposure (work) restrictions are warranted
* secure long-term retention of medical records 
Reference Article
Double US Occupational Safety and Health Administration (OSHA). Occupational Exposure to Respirable Crystalline Silica -- Review of Health Effects Literature and Preliminary Quantitative Risk Assessment [2010]
UK Health and Safety Executive (HSE). Health surveillance in silica exposed workers. [2010]

Lappi VG et al. Silica exposure and silicosis in Alberta, Canada. J Occup Environ Med. 2014 Oct;56 Suppl 10:S35-9.

American Conference of Governmental Industrial Hygienists (ACGIH). Recommendations for a Threshold Limit Value – Crystalline Silica. [2010]

US National Institute for Occupational Safety and Health (NIOSH). Health Effects of Occupational Exposure to Respirable Crystalline Silica. [2002]

Dahmann et al. Assessment of exposure in epidemiological studies: the example of silica dust. Journal of Exposure Science and Environmental Epidemiology (2008) 18, 452–461
Raymond LW and Wintermeyer S. Medical Surveillance of Workers Exposed to Crystalline Silica. JOEM (2006) 48;1 95-101
UK Health and Safety Executive (HSE). Variability in fibrogenic potency and exposure-response relationships for silicosis. EH75/4
(2002)