Transient application, recirculating pool fire, agent effectiveness screen:

Abstract

NISTIR 6733ii EXECUTIVE SUMMARY * Because of its many positive attributes, halon 1301, or trifluorobromomethane (CF 3 Br), has been used as a fire extinguishing agent in many applications including aircraft, ships, and specialized structures. Due to its high ozone depletion potential, however, world-wide production was halted in 1994. In the search for a long-range replacement, novel types of extinguishing agents and delivery mechanisms are under development. To gauge the suitability of a replacement agent, methods are needed to evaluate the material's suppression effectiveness under conditions that relate to field applications.In this study, a laboratory-scale facility has been developed to screen the suppression effectiveness of agents that are delivered in a transient fashion such as solid propellant gas generators. The transient application, recirculating pool fire (TARPF) agent effectiveness screen features a propane fire stabilized behind an obstruction, which is known to be a highly challenging suppression configuration. The character of the flame and the impact of the air flow, fuel flow, obstruction geometry, and rate of agent addition on the amount of material needed for suppression are evaluated for N 2 , CF 3 Br, and a solid propellant gas generator (SPGG). The importance of the injection process on the flow field and the transport of the agent downstream is examined, and a simple mixing model is used to explain the observed trend of decreasing suppressant mole fraction with increasing injection duration, even for agents as different as CF 3 Br and N 2 . Direct numerical simulation of the suppression event is shown to successfully predict the quantity and rate of N 2 required to extinguish the flame based upon a published global reaction rate for premixed propane/air flame propagation. Important Findings:• The minimum mole fraction of agent for suppression, normalized by the cup burner value, correlates with [1 -exp(-∆ t/ τ )] -1 , where ∆ t is the injection time interval and τ characterizes the mixing time behind the obstacle in the flow.• The general character of the flame and its extinction by a thermal gaseous agent is captured by a direct numerical simulation of the flow based upon single -step chemistry, and numerical experiments have corroborated the simple correlation of the experimental data for N 2 .• The measured difference between the decrease in agent storage bottle pressure and the arrival of the agent at the fire highlight the importance of determining the agent concentration locally and the difficulty in relating changes in bottle pressure to actual mixing conditions. • For the first time, both compressed and solid-propellant generated gases can be compared side by side, and the effect on performance of different formulations, particle loadings and burning rates for various SPGG designs can be unambiguously discriminated.• When the temperature of a hot surface downstream of the pool is above 800 o C, the flame, following suppression, will reignite and stabilize on the hot surface. At ...

Testing ogranophosphorus, organofluorine, and metal-containing compounds and solid-propellant gas-generating compositions doped with phosphorus-containing additives as effective fire suppressants

“…In practice, the MEC value for which there is no reignition of TMP vapor is 8.5% at an air temperature of 90 • C. The minimum extinguishing concentrations for CF 3 Br were de- termined at a temperature of 16-75 • C and are given in Table 5 and in Fig. 5, together with the data for (CF 3 CH 2 O) 3 P, whose MECs were determined at a temperature of 35-86 • C. The results for CF 3 Br are in good agreement with the data of [12], which were obtained at room temperature (3.1% by volume). The results given in Fig.…”

“…Ignition was performed by a spark igniter. As shown in [12], variation in the volume flow rate of propane through the burner in the range of 10-100 cm 3 /sec does not affect the suppression process. The suppression process was recorded by a video camera.…”

“…However, most of these data do not allow one to determine the minimum extinguishing concentrations of OPCs in practice; they only make it possible to arrange the compounds in increasing order of flame suppression effectiveness. Thus, in spite of the significant number of theoretical and experimental studies of organophosphorus suppressants, no data have been reported on their flame suppression effectiveness in bench test conditions simulating realfire scenarios, as was done for CF 3 Br in [12]. It is of interest to run such fire-extinguishment tests for flames of various types, which would allow conclusions concerning the expediency of large-scale tests and practical applications of new flame suppressants.…”

“…The suppression process was recorded by a video camera. For the case of CF 3 Br, it has previously been established [12] that the extinguishing concentration depends on the duration of supply of the flame suppressant and reaches the minimum value in not less than 1 sec. Therefore, in spite the possibility of changing the duration of supply of the flame suppressant, it remained constant and was 1 sec in all experiments.…”

“…The suppression of a turbulent flame with transient injection of a flame suppressant into an air flow was studied on a setup similar in dimensions and design to that used in [12]. The setup simulates the aeroengine flame extinguishing conditions.…”