Air monitoring and medical surveillance
Air monitoring and medical surveillance are the two feedback loops of a HAZWOPER program: one measures the workplace in real time, the other measures the worker over a career. Exam items tend to be scenario-based - interpret a four-gas reading, choose a monitoring strategy, or decide who belongs in the medical program.
Monitoring strategy
Characterize first with direct-reading instruments, then confirm with validated methods and personal samples. The core suite is a four-gas meter (oxygen, combustible gas as %LEL, carbon monoxide, hydrogen sulfide), plus a PID or FID for volatile organics and colorimetric tubes for specific gases. Know the limits: PID response depends on lamp energy and the compound's ionization potential, and an LEL sensor calibrated to methane misreads other flammable vapors without a response factor.
Instrument discipline: bump test before each day's use, calibrate per the manufacturer, and record both. Set action levels - commonly 10% LEL, oxygen outside 19.5–23.5%, and any reading approaching an exposure limit or IDLH - and define what happens when one is reached: stop, ventilate, upgrade PPE, or evacuate.
Medical surveillance under 1910.120(f)
Covered employees include those exposed above a PEL for 30 or more days a year, those wearing a respirator 30 or more days a year, hazardous materials team members, and workers injured or made ill by exposure. The program provides a baseline exam before assignment, periodic exams (generally annual), and an exam at termination. Records are kept for the duration of employment plus 30 years and are accessible to the employee. A respirator medical evaluation under 1910.134(e) is a separate, earlier gate - you cannot fit test first.
Worked example
A four-gas meter in a utility vault reads 20.2% oxygen, 12% LEL, 3 ppm hydrogen sulfide, and 6 ppm carbon monoxide. Oxygen is acceptable, but 12% LEL exceeds the 10% action level and the atmosphere is trending flammable, with toxic gases present. Decision: no entry, withdraw, ventilate, and re-monitor from outside. Do not watch the reading for a minute - the LEL is climbing.
Traps
Treating one instrument reading as proof of safety, ignoring calibration drift, or reading %LEL as a concentration. Confusing respirator medical clearance with the HAZWOPER surveillance exam, and forgetting that exposure records must be kept 30 years.