Couch in the corner of a room after a fire

FSRI Releases Report - Residential Flashover Prevention with Reduced Water Flow: Phase 2

November 9, 2021

During phase 2 of the "Residential Flashover Prevention with Reduced Water Flow" experiments were conducted to examine if a conical water spray that directly cools the fuel can be scaled up to prevent flashover in larger rooms while maintaining the reduced water flow demand for the system. The low flow nozzle system tested in this study reliably delayed fire growth, but would not reliably prevent flashover. The full report that can be downloaded at the bottom of this page. 



The purpose of this study was to investigate the feasibility of a residential flashover prevention system with reduced water flow requirements relative to a residential sprinkler system designed to meet NFPA 13D requirements. The flashover prevention system would be designed for retrofit applications where water supplies are limited. In addition to examining the water spray’s impact on fire growth, this study utilized thermal tenability criteria as defined in UL 199, Standard for Automatic Sprinklers for Fire-Protection Service. The strategy investigated was to use full cone spray nozzles that would discharge water low in the fire room and directly onto burning surfaces of the contents in the room. Where as current sprinkler design discharges water in a manner that cools the hot gas layer, wets the walls and wets the surface of the contents in the fire room.

A series of eight full-scale, compartment fire experiments with residential furnishings were conducted with low flow nozzles. While the 23 lpm (6 gpm) of water was the same between experiments, the discharge density or water flux around the area of ignition varied between 0.3 mm/min (0.008 gpm/ft2) and 1.8 mm/min (0.044 gpm/ft2). Three of the experiments prevented flashover. Five of the experiments resulted in the regrowth of the fire while the water was flowing. Regrowth of the fire led to untenable conditions, per UL 199 criteria, in the fire room. At approximately the same time as the untenability criteria were reached, the second sprinkler in the hallway activated. In a completed system, the activation of the second sprinkler would reduce the water flow to the fire room, which would potentially lead to flashover. The variations in the burning behavior of the sofa resulted in shielded fires which led to the loss of effectiveness of the reduced flow solid cone water sprays. As a result of these variations, a correlation between discharge density at the area of ignition and fire suppression performance could not be determined given the limited number of experiments.

An additional experiment using an NFPA 13D sprinkler system, flowing 30 lpm (8 gpm), demonstrated more effective suppression than any of the experiments with a nozzle. The success of the sprinkler compared with the unreliable suppression performance of the lower flow nozzles supports the minimum discharge density requirements of 2 mm/min (0.05 gpm/ft2) from NFPA 13D. The low flow nozzle system tested in this study reliably delayed fire growth, but would not reliably prevent flashover.

Research Project: Residential Flashover Prevention Research
Report Title: Residential Flashover Prevention with Reduced Water Flow: Phase 2
Report Authors: Nick Dow and Daniel Madrzykowski
Download the Report:
Release Date: November 9, 2021

Residential Flashover Prevention Research