Hazard Classification and Design Criteria
What this domain tests
This domain tests whether you can classify an occupancy or commodity correctly and then select the density, design area, and hose allowance. The exam focuses on light, ordinary, and extra hazard groups, plus the separate storage chapters that override simple occupancy labels.
Core rules and concepts
- Light hazard includes offices, schools, churches, and similar low-fuel occupancies. Typical starting criterion is 0.10 gpm/ft2 over 1,500 ft2.
- Ordinary Hazard Group 1 includes parking garages, laundries, and machine shops; typical criterion is 0.15 gpm/ft2 over 1,500 ft2. Ordinary Hazard Group 2 includes woodworking, paper processing, and similar moderate-fuel areas; typical criterion is 0.20 gpm/ft2 over 1,500 ft2.
- Extra Hazard Group 1 starts at 0.30 gpm/ft2 over 2,500 ft2; Extra Hazard Group 2 starts at 0.40 gpm/ft2 over 2,500 ft2.
- Storage occupancies are classified by commodity, storage height, aisle width, and ceiling height, not by a simple light/ordinary label.
- Dry-pipe and double-interlock preaction systems increase the design area by 30 percent.
Worked example
A 2,000 ft2 cabinet-assembly room uses finished wood, glue, and cardboard packaging. The fuel load is moderate and the operation is not a high-piled storage array. Classify it as Ordinary Hazard Group 2: 0.20 gpm/ft2 over 1,500 ft2 gives 300 gpm sprinkler demand. Add 250 gpm hose allowance for ordinary hazard, for a total of 550 gpm. If the room were protected by a dry-pipe system, the design area would increase to 1,950 ft2, raising sprinkler demand to 390 gpm before hose allowance.
Traps that cost marks
- Classifying by business name rather than fuel load and process.
- Treating a storage area as Ordinary Hazard 2 when Chapter 20 storage criteria govern.
- Forgetting the 30 percent dry-system area increase.
- Using the wrong hose allowance for the hazard.
- Applying a density without checking the actual design area shape and ceiling height.
Exam approach
Identify the occupancy and the commodity first. Check whether storage chapter criteria apply. Then select density and area, apply system-type increases, and add hose allowance.