Hazard Identification and Risk Assessment
This domain tests whether you can find hazards before they cause harm, choose an assessment method that fits the task, score and rank risk reproducibly, and select controls in the correct order.
Finding hazards
- Routine sources: walkthroughs, inspections, job hazard analysis for non-routine and high-consequence tasks, incident and near-miss trends, worker reports, exposure monitoring, and change review.
- Formal methods: HAZOP applies guide words to process nodes and parameters; FMEA scores failure modes by severity, occurrence, and detection; fault tree analysis works backward from a defined top event; bow-tie diagrams map threats, the top event, consequences, and barriers.
- Match method to stage: HAZOP and FMEA fit design-stage process risk, JHA fits task-level risk, and fault tree fits a single serious outcome you need to decompose.
Exposure limits
- OSHA permissible exposure limits are enforceable; ACGIH threshold limit values and AIHA workplace environmental exposure levels are guidance values and are often lower.
- Limits are time-weighted over eight hours, with short-term exposure limits (typically 15 minutes) and ceilings for some agents. IDLH values drive respirator selection and escape planning.
- Noise: hearing conservation program at the 85 dBA TWA action level, PEL of 90 dBA TWA under 1910.95.
- Personal breathing-zone samples represent worker exposure; fixed-area samples do not.
Scoring and controls
- Risk = likelihood × severity on a matrix, with written criteria so two assessors reach the same score. Re-score residual risk after controls.
- Hierarchy of controls: elimination, substitution, engineering, administrative and work practice, then PPE. PPE depends on fit, training, and consistent use, so it is the last line.
- PPE selection requires a hazard assessment certified in writing under 1910.132(d).
Worked example
An open-top vapor degreaser exposes three workers to solvent vapor for a full shift. Initial scoring: likelihood 4 (continuous exposure, no local exhaust), severity 4 (chronic neurological effects) = 16, high risk. First option is substitution to an aqueous cleaning process, which removes the exposure. If substitution fails, add local exhaust ventilation at the tank lip, cutting likelihood to 2; add work-practice limits on dwell time. Residual score 2 × 3 = 6, medium. Issuing respirators alone would leave likelihood near 4, because respirators fail silently when fit or use is poor.
Traps that cost marks
- Labeling PPE as elimination or as an engineering control.
- Assessing only normal operation and skipping startup, shutdown, maintenance, and jam clearing.
- Reading a low injury rate as proof of low risk; exposure and near-miss data may say otherwise.
- Treating threshold limit values as legally enforceable.
- Using area sampling results to represent individual exposures.