Occupational Safety and Health
Controls and limits
OSHA requires controls in order: elimination, substitution, engineering controls, administrative controls, and only then PPE as the last line of defense. Distinguish the exposure limits, a reliable source of wrong answers. OSHA PELs are enforceable legal limits, mostly 8-hour time-weighted averages, with some ceiling and short-term limits. ACGIH TLVs and NIOSH RELs are health-based recommendations, and RELs are often lower than the corresponding PEL.
HAZWOPER training
Under 29 CFR 1910.120(e), general site workers need 40 hours of instruction plus three days of supervised field experience. Workers on site only occasionally for a specific, limited task, and unlikely to exceed exposure limits, need 24 hours plus one day of field experience; so do workers at fully characterized sites where respirators are not required. Supervisors need 24 additional hours, and everyone needs an 8-hour annual refresher, medical surveillance, and annual respirator fit testing.
PPE levels
Level A is a fully encapsulating suit with SCBA, the highest skin and respiratory protection. Level B is SCBA or supplied air with chemical-resistant clothing giving splash but not vapor protection. Level C is an air-purifying respirator with the correct cartridge, used only when the concentration is known and below IDLH. Level D is a work uniform.
Traps
- Oxygen below 19.5% is an IDLH atmosphere; never use an air-purifying respirator there.
- Never use an APR for unknown concentrations or above IDLH.
- TWA is time-weighted, not a simple arithmetic average of samples.
Worked example. A worker spends 4 hours at 200 ppm and 4 hours at 50 ppm, so TWA = (200×4 + 50×4) ÷ 8 = 125 ppm. Compare that directly to an 8-hour PEL of, say, 100 ppm to document an overexposure.