Commercial residential sprinklers are usually fitted with 3 mm glass bulbs having a nominal operating temperature of 68°C or a high-sensitivity solder link, usually with a nominal temperature rating of 74°C. Previous work show that there is a significant potential for improving sprinkler response times in a residential room fire scenario by using glass bulbs with a lower Response Time Index (RTI) and lower operating temperature than commonly used. The objective of this study was to investigate any improved performance due to earlier activation of residential sprinklers. A series of fire tests was conducted inside a test compartment sized 3.66 m by 3.66 m. The fire test source consisted of either a simulated or authentic upholstered chair. For the majority of the tests, the flow rate of the residential sprinkler was 30.3 liter/min (corresponding to the minimum design density 2.05 mm/min as per the recommendations in NFPA 13D and 13R). Additional tests were conducted at 60.6 liter/min (the minimum design density 4.1 mm/min as per NFPA 13). Tests were also conducted with commercial low- and high-pressure water mist nozzles and a stand-alone high-pressure water mist system.

The results show that earlier activation of residential sprinklers had a small effect on its performance, especially for the authentic upholstered chair scenario, when flowing 30.3 liter/min. The rather small effect is probably due to that the discharge density was too low to provide fire suppression. When the flow rate was increased to 60.6 liter/min, the performance was considerably improved as compared to the flow of 30.3 liter/min. Any improvement in performance of earlier activation was, however, not investigated for the 60.6 liter/min flow rate.

The flow rates of the commercial low- and high-pressure water mist water mist nozzles ranged from 17.2 liter/min to 36.7 liter/min. Roughly, it could be concluded that the performance of the water mist nozzles were comparable or better than the residential sprinkler at approximately half the water flow rate for the tested fire scenarios.

The stand-alone high-pressure water mist system had a flow rate of 8.2 liter/min. The performance was comparable to that of the other water mist nozzles in the study The performance was comparable to that of the other water mist nozzles in the study, despite a considerably earlier activation. However, the results indicate that the performance was relatively much influenced whether the simulated upholstered chair was orientated with its front towards the test compartment or with its front towards the back wall (poorer performance). This would suggest that the position of the fire test relative to the position of the unit is a crucial factor and underlines the importance of a thoughtful positioning in practical applications.