Fire Hydrant Flow Testing

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Fire Hydrant Flow Test Guidelines
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In general, the waters that are discharged during fire hydrant flow testing have little potential to contain pollutants.  The primary exception is chlorine, which is a common constituent of municipal waters.  However, fire hydrant flow testing generates large quantities of water with high velocity flows.  Uncontrolled, these flows can create erosions and contribute sediment to receiving water bodies.  In addition, these flows pick up other pollutants from the surfaces over which they travel and wash them to the receiving waters.


  • Prior to discharge, the areas of discharge shall be cleaned of debris, sediment, and other pollutants.
  • The primary discharge stream from the hydrant shall always be directed to rock, riprap, concrete, asphalt or other solid areas with little potential for erosion.
  • The discharge shall not cause or result in erosion to the area of the discharge or downstream areas.  Adequate detention structures and velocity dissipation devices should be used when necessary to decrease velocities, prevent erosion, reduce scouring and reduce turbidity.  When discharging to streets, gravel bags should be used to reduce flows.  When flows will travel through natural or vegetated areas, gravel bags, check dams, silt fences, fiber rolls and hay bales should be used to control the flow and reduce velocities.
  • During discharge, the downstream areas shall be monitored so as to ensure it is not causing erosion or producing other impacts.  If such a scenario occurs, the discharge should be stopped immediately and necessary measures shall be taken to clean up and correct the problem.
  • The discharger shall take into account the conveyance capacity of the discharge outlet structure and/or conveyance structure prior to discharge and shall manage or control the flow of the discharge accordingly. The discharge shall not cause or create downstream flooding conditions.

When chlorinated municipal waters are the source of water for the discharge and the discharge will travel less than 1,000 feet before entering a river, stream or other receiving water, the discharge shall be aerated and/or treated in such a way that the chlorine level is reduced or dissipated prior to discharging to the receiving waters by using sodium thiosulfate or another de-chlorination method.   If necessary, the water to be discharged can be directed through hay bales, over grassy areas or rip rap and/or otherwise sufficiently aerated, bypassing several storm sewer inlets as necessary to dissipate the chlorine prior to discharging to the receiving water body.  A pool chlorination kit can be used to confirm that there are no detectable levels of chlorine in the water prior to discharge.