Environmental and Occupational Health
Core concepts
Environmental health risk assessment has four steps: hazard identification, dose-response assessment, exposure assessment, and risk characterization. Know exposure pathways, water quality and sanitation, air pollution, solid and hazardous waste, vector control, food safety, housing, and climate-related risks. Occupational health requires hazard recognition, exposure limits such as time-weighted averages and short-term exposure limits, biological monitoring, sentinel-event reporting, and workers' compensation. The hierarchy of controls runs from elimination and substitution through engineering and administrative controls to personal protective equipment. Environmental epidemiology uses exposure biomarkers, spatial analysis, and time-series studies.
Traps
Chlorination controls many bacteria and viruses but not Cryptosporidium oocysts. PM2.5 penetrates deeply and is more harmful than larger particles. Carbon monoxide binds haemoglobin with high affinity. Personal protective equipment is the last line of defence, not the first. Exposure limits are health-based guidance and are not automatically legal limits. A single air sample may not represent personal exposure.
Worked example
A worker is exposed for 4 hours at 200 ppm and 4 hours at 100 ppm. The 8-hour time-weighted average = (200×4 + 100×4)/8 = 150 ppm. Compare this with the 8-hour limit, then check whether any short-term peak exceeds the short-term limit. Controls should first reduce the source, not merely issue masks.
Rule of thumb
Control at the source, then along the path, and only lastly at the worker.