Core Concepts
Exposure Assessment
The process of measuring or estimating the magnitude, frequency, and duration of exposure to workplace hazards.
PEL (Permissible Exposure Limit)
OSHA's legal limit on the concentration of a substance in workplace air.
TLV (Threshold Limit Value)
ACGIH's recommended airborne exposure limit for chemical substances and physical agents.
PPE (Personal Protective Equipment)
Equipment worn to minimize exposure to hazards: gloves, masks, goggles, respirators, etc.
Ventilation
The use of local exhaust and general dilution ventilation to control airborne contaminants.
Hierarchy of Controls
Elimination → Substitution → Engineering Controls → Administrative Controls → PPE (most to least effective).
Worked Examples & Applications
Hierarchy of Controls Example: Chemical solvent exposure: 1) Eliminate (remove chemical) 2) Substitute (use safer alternative) 3) Engineering (install ventilation) 4) Administrative (reduce exposure time) 5) PPE (gloves and respirator).
OSHA PEL Calculation: 8-hour TWA = (C₁×T₁ + C₂×T₂ + ... + Cₙ×Tₙ) / 8 where C = concentration in ppm/mg/m³ and T = exposure time in hours. If result exceeds PEL, action is required.
Practice Questions
Q: What is the most effective control in the hierarchy? A: Elimination — completely removing the hazard from the workplace.
Q: What is a TWA? A: Time-Weighted Average — the average exposure over a specified period, typically 8 hours.