Fire station planning principles Example of fire response coverage area calculation using SANS 10090 A worked example of coverage area for a fire station to meet Category ‘A’ fire risk travel time of five minutes based on the estimated appliance speed of 30km/h would look like: STEP 1: Calculate linear travel distance Distance = speed x time Where: d=? s= 30km/h t = ,08 hours ie five minutes travel time required for category A fire risk divided by 60 minutes Thus: d = 30 x 0,08 = 2,4 km is the distance that can be travelled in five minutes at 30 km/h STEP 2: Establish polygon
NFPA 1710 methodology Taking into account that the NFPA 1710 is provision of SANS 10090, the American system considers the distribution of fire stations based on the required response times (table 3) for the area protected rather than risk protected and on the Fire Suppression Rating Schedule (FSRS), which is an analysis tool of the Public Protection Classification (PPC™) programme of the Insurance Service Office-USA (ISO).
This criteria produces 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 New York City RAND Institute (USA). 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 (56.32kmh). This average 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:
STEP 3: Establish polygon
Figure 3: RAND Institute equation for calculation of travel time
STEP 4: Factor 25 percent deduction allowance SANS advises that an allowance of 25 percent must be deducted in order to make provision for complexities of street grid networks. = 15,02 km2 – 25 percent = 11km2 is the area to be covered with five minute response window travelling at 30km/h. STEP 5: Repeat step 1 to Step 4 for B, C and D categories Using the same travel speed (30km/h) but the different maximum time requirements for each remaining fire risk category; calculate the fire response coverage areas for B, C and D fire risk categories. STEP 6: Overlay polygons on map
Calculations on SANS and NFPA methodologies It is suggested (as essential) that when planning for optimal siting of future fire stations, that both the SANS and NFPA methodologies for calculation, where one is risk categorybased and the other community centric, be utilised. The results for optimal siting of fire station will then be based on variable ranges of risk, maximum required travel times, estimated speed of appliance, distance, resultant coverage areas that when inputted into the RAND equation, will provide resultant average travel time to actually cover the road kilometres. The tables below show the calculations for the categories of fire risk based on maximum travel times, estimated speeds of appliance and actual time to cover the road kilometre distance. Table 1: Fire response coverage for category A fire risks
Consolidate polygons for each risk category and overlay on map to provide indicative fire response coverage for each risk category. Map and polygon shown below only for illustrative purposes 32 | FIRE AND RESCUE INTERNATIONAL
Volume 4 | No 1