Inert gas extinguishing systems: Preventing reignition

A standardized test evaluates total flooding inert gas extinguishing systems to ensure the agent and discharge system can extinguish a representative fire threat. The standardized test criteria are extinguishing the test article and preventing reignition after a 10-minute soaking period and exposure to fresh air. Much is still unknown about how the joint discharge effects of reduced oxygen concentration and the increased flow of agent and entrained air near the crib lead to total extinguishment (gas and solid phase) and reignition prevention. Wood cribs of 3 different wood species were instrumented with thermocouples, S-type pitot tubes, and a mass balance in a reduced-scale inert gas testing enclosure to study reignition. The standardized test timeline was maintained except for the soak period, which was reduced to a range of 30 s to 6 min. Results indicate that reingition is possible at lower soak periods. However, the standard wood species of Douglas fir was not observed to reignite, leaving the usefulness of the selected material questioned. Recommendations are made for further testing and potential changes in the testing approach. • Reignition (smoldering-to-flaming transition) is evaluated after gas phase suppression of a wood crib resulting from a total flooding inert gas discharge. • Reignition was not observed with the Listing Laboratory specified species, Douglas fir. However, reignition was observed for other non-standard wood species and shorter than standard soak periods. • Suggestions are made to improve the standardized extingusing test.