Identification and Chemical/Physical Properties
Identification and Chemical/Physical Properties
Identification answers 'what is it?'; properties answer 'how will it behave?' The exam tests the hierarchy of identification and the response meaning of physical data.
Core rules
- Use a hierarchy: shipping papers and UN/NA numbers, placards and labels, SDS and product labels, facility documents, CHEMTREC/CANUTEC, CAMEO/WISER, then field detection. No single clue is definitive.
- Vapor density greater than 1 tends to collect in low areas; less than 1 tends to rise. Specific gravity greater than 1 sinks in water; less than 1 floats.
- Vapor pressure indicates tendency to become airborne. Flash point is the lowest temperature at which a liquid gives enough vapor to ignite; it is not autoignition temperature.
- LEL/UEL bracket the flammable range. Water solubility affects runoff, foam selection, and whether water can spread the product.
- Reactivity, pH, corrosivity, and incompatibles determine container and PPE choices.
Worked example
A tanker placarded UN 1789 is leaking. UN 1789 is hydrochloric acid. The material is corrosive, water-soluble, and can release corrosive vapor. A low-lying pool is less likely than with a dense flammable vapor, but the acid can run into drains and react with metals to generate hydrogen. Response reasoning: isolate, stay upwind, keep people away from runoff, use acid-compatible PPE, and avoid uncontrolled water application that spreads corrosive runoff. The UN number narrows the identity, but concentration and additives still matter.
Traps
- Treating a UN number or placard as a full product specification.
- Confusing flash point with ignition temperature.
- Assuming 'heavier than air' always means every vapor stays low; temperature and wind matter.
- Using water on a water-reactive material.
- Ignoring product-specific SDS sections for incompatibles.