In evaluating a community's public fire protection, ISO considers the distribution of fire companies. Generally, ISO's criteria say that a built-upon area of a community should have a first-due engine company within 1.5 road miles of the protected properties and a ladder-service company within 2.5 road miles.
Those benchmark criteria produce an expected response time of 3.2 minutes for an engine company and 4.9 minutes for a ladder-service company, based on a formula developed by the RAND Corporation.
RAND conducted extensive studies of fire department response times. They concluded that the average speed for a fire apparatus responding with emergency lights and siren is 35 mph. That speed considers average terrain, average traffic, weather, and slowing down for intersections.
Taking into account the average speed and the time required for an apparatus to accelerate from a stop to the travel speed, RAND developed the following equation for calculating the travel time:
||time in minutes to the nearest 1/10 of a minute
||a vehicle-acceleration constant for the first 0.5 mile traveled
||a vehicle-speed constant validated for response distances ranging from 0.5 miles to 8.0 miles.
ISO, working with several fire departments, recently conducted its own review of the formula and found the earlier RAND work still valid as a predictive tool.
In our analysis of company distribution, ISO does not measure or use actual historical response times of individual communities. Many fire departments lack accurate and reliable response-time information, and there is no standardized national recordkeeping system that would allow us to determine accurate departmental response times.
Also, it would be inappropriate to incite fire service personnel to push fire apparatus beyond a safe driving speed for the sake of faster response times, especially since U.S. Fire Administration statistics for 2005 indicate that 17 percent of firefighter on-duty fatalities resulted from responding to alarms.
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