Hazard Identification and Recognition
What the candidate must know
Hazard identification starts before contact: shipping papers, placards and labels, NFPA 704 and DOT markings, container shapes and sizes, facility pre-plans, and chemical reference sources (ERG, SDS, CAMEO). Recognize that placards indicate the hazard class of the contents in bulk, not a specific chemical identity, and that a placard may be absent on empty or residue containers. Understand the difference between identification (what it is) and recognition (that something is hazardous), and know the clues: occupancy and location, container shape, markings, sensory clues, and behavior of the release.
Traps in questions
- Treating a placard number as a UN/NA identification number; the four-digit number is the ID, the placard color/class is the hazard.
- Assuming odor is a reliable indicator; many chemicals are odorless or have odor thresholds above or below harmful concentrations.
- Forgetting that pipeline markers, rail car shapes (pressure vs. non-pressure), and tank configurations are recognition clues.
- Confusing DOT hazard classes with NFPA 704 health/fire/instability ratings; they answer different questions.
Rule of thumb
Identify from a distance using the most reliable source available, in this order: shipping papers/waybill, then placards/labels/markings, then container shape and facility knowledge, then reference sources. Never approach to read a label you cannot read safely.
Worked example
A rail tank car with a white placard bearing a four-digit number and a skull-and-crossbones: the class indicates a toxic hazard; the four-digit number is looked up in the ERG to get guide number, isolation distances, and protective clothing. The tank car shape (pressure car) narrows the product family before the number is confirmed.