Inert gas discharge time effects on full and reduced scale wood crib extinguishing experiments

The 2012 edition of NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems, was revised to allow a maximum 2-min discharge duration for systems that protect class A fire hazards with inert gases. With this change, UL 2127 and FM 5600 also began testing and certifying systems over both 60- and 120-s discharge durations. This study analyzes the effect of the different discharge times of an inert agent on the extinction of a test article (wood crib) placed within an enclosure. This was done following the UL 2127 procedure, and a modified version of it that involved the use of a reduced-scale experimental setup. The enclosure was scaled based on the oxygen consumption of the wood crib. Observations and measurements included oxygen concentration within the enclosure, near-crib gas velocity and temperature, as well as wood crib mass. These quantities were used to study the extinguishment differences at the two discharge durations and support the validity of a novel ¼ reduced-scale crib and enclosure developed in this study. It was found that varying the discharge time will induce changes in the suppression dynamics, as the flow of agent and entrained air affect the time to reach extinction. •Recent changes in the discharge period allowed by NFPA 2001 were thought to change the minimum extinguishing concentration.•Near-field extinguishing effects on a wood crib were studied following the UL 2127 and FM 5600 extinguishing test methods.•A scaling methodology for a reduced scale test article and enclosure are presented.•No change in agent extinguishing concentration was observed at either scale or discharge period.•Flow effects of agent and entrained air alter the burning rate of the test article during the suppression event.