Assessing hydrant coverage within a fire district

For the final project for a class, I took a look at how to delineate the area of a fire district that can reasonably be serviced by existing fire hydrants. The topic came up because firefighters are interested in seeing how far they can stretch an engine’s large-diameter hose from the nearest hydrant. They could use such maps to train new people unfamiliar with the reach of the hydrant network into rural areas. And the map data could be used to cross-check CAD data that automatically dispatches tenders to fires at certain addresses.

Another practical application of this work would be the prioritization of installing additional hydrants. One could easily see where can a hydrant could be added on or near existing water mains to serve the highest number of previously unserved structures.

“For effective firefighting it is of crucial importance that there are sufficient fire hydrants and that they are properly maintained” (Nisanci 2010). A fire engine arrives on scene with perhaps two to four minutes of water supply on board — connection to a hydrant or service from a team of slow-moving water tenders (tanker trucks) is therefore essential in the case of a working structure fire.

Methods

Hydrant coverage was calculated as 1000′ along the road network from each hydrant to account for the ability of a standard fire engine to deploy up to 1200′ of large-diameter hose from a hydrant to a fire scene (leaving 200′ for driveway length and hose routing). This type of buffer was calculated using the Service Area feature of Network Analysis in ArcGIS, because large-diameter hose can only practically be deployed along roadways.

In addition, a standard buffer was added to the coverage area defining a 400′ radius around each hydrant. This accounts for coverage from some hydrants that are not located on roadways or are at the end of roads but ostensibly could be utilized in the immediate vicinity (i.e. at the airport or a school).

These buffers were combined into a single layer, which was subtracted from the district’s boundary polygon, yielding a layer showing the areas not effectively served by hydrants.

Results

Sample detail of the map to ensure no further use of this unvetted analysis. Hydrants are circles colored by max water flow. The muted red shading is the area not reachable either within 1000′ by road (shown on the right) or 400′ in a direct line (shown on the left) from a hydrant.

The map above shows the un-hydranted areas of the district shaded in red. Of the 16,384 structures located within the boundaries of the district, 4,285 are located beyond hydrant coverage. Most hydrants are concentrated within the city.

Discussion

This fundamental output of the analysis can be used both in fire response (adaptation to the problem) and in adding hydrants (mitigation of the problem).

First, the map above can be used in greater detail to provide firefighters a concise expectation of where they will have effective hydrant coverage versus where they will need a tender-based water supply. The layer file can also be imported into the 911 center’s computer-aided dispatching system to automate tender response where it will be required.

Again, a detail of the map showing in blue-to-yellow heat map the high concentrations of structures that lie in the area unserved by hydrants.

Second, we can use this analysis to respond to the problem by adding fire hydrants where they are especially needed. For this purpose we turn to the map above, which is a heat map showing relative concentration of structures that are beyond hydrant coverage. The areas of high concentrations of significant size would, provided water lines are located nearby, be logical neighborhoods in which to add fire hydrants.

As with the first map, the muted red shades areas unserved by hydrants, and hydrants are shown as colored dots. The black squares are structures located in the unserved area.

Above is an area from the heat map in greater detail. It features a concentration of structures located adjacent to hydrant coverage but in the uncovered, shaded area. Given the adjacent water supply, areas such as this present opportunities for near-term addition of relatively few hydrants to better protect high concentrations of structures.

Suggestions for future study include performing fire-flow analysis based on building construction type, occupancy type and size and comparing required water flow to available water flow for each structure. Kaufman and Rosencrants (2014) describe a GIS-based method for doing and provide the tables necessary to make the calculations. Given the necessary inputs for structures, GIS would make such an analysis practical.

References and Data Sources

Road centerline, trail. park and district boundary data from Jefferson County GIS. Hydrant data from City of Port Townsend GIS and Jefferson Public Utility District GIS. Hydrology and structure data from WA Department of Natural Resources.

Kaufman, M. M., & Rosencrants, T. (2015). GIS method for characterizing fire flow capacity. Fire Safety Journal, 72, 25-32. doi:10.1016/j.firesaf.2015.02.001

Nisanci, R. (2010). GIS based fire analysis and production of fire-risk maps: The Trabzon experience. Scientific Research and Essays, 5(9), 970-977. Retrieved December 13, 2020, from https://academicjournals.org/journal/SRE/article-abstract/DDFB12518871