Manually-suppressed fires require about twice the number of firefighters and apparatus than sprinkler-suppressed fires. Depending upon the scope of the ordinance, the fire official will need to describe the varying suppression requirements in the different occupancies. Fire department deployment studies describe the risk categories for different structures, and the RFSI has examples. A typical study will use five risk categories: minimum, low, moderate, high and maximum.
The categories of structural fire risk are defined in terms of the demand that a pre-flashover fire places on fire suppression crews, in other words the minimum number of firefighters and apparatus needed to stop a pre-flashover fire. For example, a single-family detached dwelling requires a minimum of 12 firefighters, three apparatus and a supervisor to handle a working fire with a reasonable degree of safety. The RFSI has examples for each risk level, as well as the maximum response times deemed adequate to get the firefighters to the fire scene.
The fire official's immediate reaction to this might be to say, "Why be so restrictive? After all, many fire departments simply are not staffed and equipped to stop fires at the pre-flashover stage." The RFSI reply is, "Every fire department can stop a fire at the pre-flashover stage - if sprinklers are installed." There is no valid reason for setting fire suppression goals at anything less than stopping loss before flashover.