Hazard Recognition and Identification
Hazard recognition is the first tactical decision: you cannot protect against what you have not identified. Candidates must know the recognition clues that appear in scenarios - occupancy and container type (rail tank cars, MC/DOT cylinders, totes, drums), placards and labels, shipping papers, facility pre-plans and SDSs, NFPA 704 markings, pipeline markers, and sensory clues such as vapor clouds, dead vegetation, or unusual odors. Understand the difference between recognition (something is wrong) and identification (what the substance is), and that identification drives ERG guide selection, PPE, and isolation distances.
Traps in questions: treating an odor as proof of identity (odor thresholds vary; some toxic gases are odorless, and olfactory fatigue misleads); assuming a placard names a specific chemical when it names a hazard class; and forgetting that shipping papers may be inaccessible or wrong in a spill. Another common trap is confusing container shape with contents - a white cylinder is not automatically a specific gas, and a tank car's dome position does not guarantee a single product. Questions also test the order of operations: approach from upwind/uphill, establish command, and identify before committing resources.
Rule of thumb: recognize, isolate, then identify - never let identification delay initial isolation and notification. Use the ERG's four-digit UN/NA number and name index rather than guessing from the placard alone.
Worked example: A placard reads "FLAMMABLE" with UN 1203. You do not have a specific chemical from the placard, but the UN number resolves to gasoline - enabling guide selection, isolation, and ignition-source control.