Domain 5: Hazardous Materials, Processes, and Special Storage
This domain covers the conditions most likely to produce a catastrophic incident: hazardous materials, flammable and combustible liquids, LP-gas, high-piled storage, dust-producing operations, and hot work. Items ask you to convert the quantities you see in a room into the correct code threshold, then into the right occupancy, separation, cabinet, or permit requirement.
Quantities and control areas
- The maximum allowable quantity table sets limits per control area by hazard class and physical state. Allowable quantities can be increased by sprinkler protection, fire-resistive construction, and grade-level location, applied in the defined order.
- Quantities aggregate across all materials of the same hazard class in the control area; they are not evaluated one container at a time.
- Exceeding the maximum allowable quantity converts the space to a Group H occupancy, with H-1 through H-5 subclasses based on the material.
Cabinets and separation
An approved flammable-liquid storage cabinet may hold no more than 120 gallons of Class I, II, or III liquids, and no more than 60 gallons of Class I or Class II liquids. Incompatible materials must be segregated. High-piled storage above the code threshold requires a permit and a sprinkler design evaluated for the commodity and storage arrangement - not the original design assumption.
Hot work
Hot work requires a permit, clearance of combustibles within 35 feet or protection with guards, a fire watch during the operation and for at least one hour after, and a final check of the area after the watch ends.
Worked example
A maintenance room holds two 55-gallon drums of a Class II combustible liquid and 30 gallons of a Class IB liquid - 140 gallons total. Reasoning: the 120-gallon cabinet limit, with a 60-gallon cap for Class I and II liquids, means a single cabinet cannot be used to comply. Evaluate the combined quantity against the maximum allowable quantity per control area for the occupancy; if the limit is exceeded, a Group H classification or a properly separated storage room is required.
Traps that cost marks
Applying cabinet limits as though they were room limits; ignoring aggregation across classes; forgetting the high-piled storage permit; assuming LP-gas installations are exempt from permits and separation distances.