Safety, Health, and Environment
What to master
The hierarchy of controls (elimination, substitution, engineering controls, administrative controls, PPE -- in that order of preference), hazard identification and risk assessment (risk as probability times consequence), job hazard analysis, lockout/tagout, confined-space entry, machine guarding, electrical safety, fall protection, and fire prevention. Industrial hygiene: routes of exposure, air sampling, time-weighted averages, permissible exposure limits and threshold limit values, noise exposure in dBA and the 5 dB exchange rate, heat stress, and ventilation. Environmental topics: Clean Air Act and Clean Water Act permitting, RCRA hazardous waste identification and manifesting, spill reporting, stormwater, air dispersion basics, and waste minimization. Also know Safety Data Sheets, hazard communication, incident investigation and root-cause analysis.
Traps
- PPE is the last resort, not the first answer: engineering controls outrank administrative controls and PPE.
- Noise is logarithmic -- doubling identical sources adds about 3 dBA, not double the dBA value.
- A TWA must be weighted by hours of exposure and normalized to an 8-hour shift.
- Concentration times time is dose; comparing a short high exposure directly to an 8-hour PEL is wrong without weighting.
Worked example
A worker is exposed to 85 dBA for 4 hours and 95 dBA for 4 hours. A proper noise dose weights each level by duration against its allowable time (roughly 8 h at 85 dBA); the 95 dBA segment alone carries a much shorter allowable duration, so the combined dose exceeds 100% even though neither segment ran a full shift.
Rule of thumb: control the hazard at the source before protecting the worker, and always convert measured exposures to shift-weighted values before comparing to a limit.