One of the goals of a water distribution system is to provide adequate capacity to fight fires. HAMMER CONNECT's powerful fire flow analysis capabilities can be used to determine if the system can meet the fire flow demands while maintaining various pressure constraints. Fire flows can be computed for a single node, a group of selected nodes, or all nodes in the system. A complete fire flow analysis can comprise hundreds or thousands of individual flow solutions-one for each junction selected for the fire flow analysis.

Fire flows are computed at user-specified locations by iteratively assigning demands and computing system pressures. The program calculates a steady-state analysis for each node in the Fire Flow Alternative. At each node, it begins by running a Steady-State analysis to ensure that the fire flow constraints that have been set can be met without withdrawing Fire Flow from any of the nodes. If the constraints are met in this initial run, the program then begins iteratively assigning the Needed Fire Flow demands at each of the nodes, and checking to ensure that the constraints are met. The program then runs another set of Steady State analyses, this time either adding the Maximum Fire Flow (as set in the Fire Flow Upper Limit input box of the Fire Flow Alternative) to whatever normal demands are required at that node, or replacing the normal demands. In either case, the program checks the residual pressure at that node, the Minimum Zone Pressure, and, if applicable, the Minimum System Pressure. If the Fire Flow Upper Limit can be delivered while maintaining the various pressure constraints, that node will satisfy the Fire Flow constraints. If one or more of the pressure constraints is not met while attempting to withdraw the Fire Flow Upper Limit, the program will iteratively assign lesser demands until it finds the maximum flow that can be provided while maintaining the pressure constraints. If a node is not providing the Fire Flow Upper Limit, it is because the Residual Pressure at that node, the Minimum Zone Pressure, or the Minimum System Pressure constraints are not met while attempting to withdraw the Fire Flow Upper Limit (or the maximum number of iterations has been reached). If a node completely fails to meet the Fire Flow constraints, it is because the network is unable to deliver the Needed Fire Flow while still meeting the pressure constraints.

After the program has gone through the above process for each node in the Fire Flow Analysis, it runs a final Steady-State calculation that does not apply Fire Flow demands to any of the junctions. This provides a baseline of calculated results that can then be compared to the Fire Flow conditions, which can be determined by viewing the results presented on the Fire Flow tab of the individual junction editors, or in the Fire Flow Tabular Report. The baseline pressures are the pressures that are modeled under the standard steady-state demand conditions in which fire flows are not exerted.

To perform a Fire Flow analysis:

1. Change the Calculation Type calculation option to Fire Flow.
2. Open the Alternatives manager (Cick the Analysis menu and select Alternatives).
3. Double click on Base-Fire Flow to open the Fire Flow Alternative editor.
4. Define the needed fireflow, fireflow upper limit, pressure constraints and the fire flow nodes selection set.
5. After all necessary fields have been entered, close the Fire Flow Alternative and Aternatives manager and click Compute.
6. Open the Fire Flow Results Browser. Only the elements that were specified in the selection set will be color coded.