William L. Grosshandler

Towards the development of a universal fire emulator-detector evaluator

Past measurements are examined of CO, CO2, H2O, H2, O2, smoke and temperature produced in standard fires of the UL and EN type. Additional measurements just above the heat release zone are suggested to obtain a more complete footprint of each standard fire, and the concept of a universal fire emulator-detector evaluator (FE-DE) is introduced. The objective of the emulator is to produce more well-controlled environments that eliminate the unavoidable run-to-run variations associated with full-scale tests. Numerical fluid dynamic computations are recommended to insert the fire source into the space being protected as a guide for detector placement and to predict system per formance under realistic conditions.

SURVEY OF FIRE DETECTION TECHNOLOGIES AND SYSTEM EVALUATION/CERTIFICATION METHODOLOGIES AND THEIR SUITABILITY FOR AIRCRAFT CARGO COMPARTMENTS.

As part of the National Aeronautics and Space Administration (NASA) initiated program on global civil aviation, NIST is assisting Federal Aviation Administration in its research to improve fire detection in aircraft cargo compartments. Aircraft cargo compartment detection certification methods have been reviewed. The Fire Emulator-Detector Evaluator (FE/DE) has been designed to evaluate fire detection technologies such as new sensors, multi-element detectors, and detectors that employ complex algorithms. The FE/DE is a flow tunnel that can reproduce velocity, temperature, smoke, and Combustion gas levels to which a detector might be exposed during a fire. A scientific literature survey and patent search have been conducted relating to existing and emerging fire detection technologies, and the potential use of new fire detection strategies in cargo compartment areas has been assessed. In the near term, improved detector signal processing and multi-sensor detectors based on combinations of smoke measurements, combustion gases and temperature are envisioned as significantly impacting detector system performance.

Flame extinction limits in CH2F2/air mixtures

Abstract To optimize the efficiency and safety of mixtures of nonozone-depleting refrigerant replacements, precise measurements of the lean flammability limits of pure refrigerants and the critical flammability ratio of their mixtures are crucial. Current test methods that model the accidental ignition of a volume of premixed fuel and air provide ambiguous results when measuring the limiting behavior of weakly flammable refrigerants. An alternative approach using the extrapolation of the global extinction stretch rates to zero as measured in a premixed counterflow burner has been tested. In this work the approach, accuracy, and precision of the technique as it applies to CH2F2 (difluoromethane, R-32) are presented. Comparisons are made to the behavior of CH4 in the same burner and to published data on the lean limiting equivalence ratio, Φ0. The lean flammability limit of CH2F2 in dry air is found to be Φ0 = 0.78 ± 0.04. Concurrent computational modeling of the combustion of a one-dimensional, unstrained flame of CH2F2 in air, individually and in mixtures with CH4, has been performed. Initial estimates of the laminar flame speed for CH2F2/air mixtures from stoichiometric to lean are reported and interpreted in light of the experimental results.

Dispersed Liquid Agent Fire Suppression Screen Apparatus

Abstract : The design, construction, demonstration, and operation of a bench-scale device capable of screening the fire suppression efficiency of liquid agents are described in detail in this report. The apparatus is based on a well-characterized flame, a means to facilitate the introduction of liquid agents, and a way to generate liquid droplets. A Tsuji-type burner, a porous cylinder used in a counterflow diffusion configuration, is used. Both wake and enveloped flames can be maintained over a wide range of fuel and oxidizer flows. The flame is easily observed, and critical stages such as the blow-off limit (abrupt transition from an enveloped flame to a wake flame) can be ascertained with ease and high reproducibility. A small-scale vertical wind tunnel, which allows for the delivery of a uniform flow of oxidizer to the burner at a low turbulence intensity and also assists in the delivery of liquid agent droplets to the flame, is used for the flow facility. Two techniques of generating droplets have been examined: (1) a piezoelectric droplet generator and (2) a small glass nebulizer. The piezoelectric droplet generator was found incapable of handling fluids with high loading of dissolved solid due to frequent clogging of the orifice opening. The nebulizer is used in the current liquid screen apparatus.

An apparatus for screening fire suppression efficiency of dispersed liquid agents

The design, construction, demonstration, and operation of a bench-scale device capable of comparison screening the fire suppression efficiency of liquid agents are described in this paper. The apparatus is based on a well-characterized flame, a means to facilitate the introduction of liquid agents, and a way to generate liquid droplets. A porous cylinder in a counterflow diffusion configuration is used. A small-scale vertical wind tunnel, which allows for the delivery of a uniform flow of oxidizer to the burner and also assists in the delivery of liquid agent droplets to the flame, is used for the flow facility. Droplets are generated by a small glass nebulizer. The performance of the screening apparatus was evaluated using several liquid fire suppressants with different thermophysical properties. A test protocol is also proposed.

Suppression of high-speed C2H4/air flameswith C1-halocarbons

Experimental investigations of the effect of the presence of five C 1 -halocarbons (CF 4 , CHF 3 , CF 3 I, CHF 2 Cl, and CF 3 Br) on the suppression of premixed high-speed turbulent flames and quasi detonations have been carried out in a 7.5-m long, 50-mm diameter tube. Lean and stoichiometric C 2 H 4 /air mixtures in the absence of any halocarbon, initially at 100 kPa and 295K, constitute the reference states. A primary objective of the work has been to determine the relative suppression efficiencies of different agents under highly dynamic situations, without the undue influence of either the ignition event of the mixing of the agent into the flame front. This was accomplished by generating a highly turublent flame/quasi detonation in the driver section, which contained no suppressant, followed by measurements of the velocity and pressure ratio as the wave front entered the test section of the tube, which contained suppressant premixed with the same fuel/air combination. A turublence generator in the form of a spiral obstruction was used in the tube to broaden the gas-dynamic conditions attainable by the flame. Flame and shock wave velocities up to 1300 m/s, pressure ratios across the shock fronts over 26:1, and shock wave/flame spacings of the order of 10 cm were measured with piezoelectric pressure transducers and fast photodiodes. The experimental facility was successfully employed to clearly discriminate among the dynamic characteristics of the five compounds, revealing behavior distinct from what was observed in companion studies using atmospheric nonpremixed flames. The suppression process is strongly influenced by the concentration of an agent, the structure and composition of an agent molecule, and the composition of the combustible mixture itself.

Rapid discharge of a fire suppressing agent

Abstract This paper describes an experimental method to study the rapid discharge of a fire suppressant (C 3 F 8 ) from a pressurized vessel. Experimental observations inside and at the exit of the vessel were made using high-speed photography. Boiling was not observed inside the vessel during discharges. A simple mathematical model was developed to predict the liquid depletion level and is compared to the experimental measurements.

Acoustic emission of structural materials exposed to open flames

The use of acoustic emission (AE) as an early indicator of structural materials exposed to a flame has been investigated and found to be possible. Piezoelectric transducers have been mounted directly on 0.5 m long, simply supported beams of aluminum, gypsum board, wood and plastic, and have been used to record ultrasonic events resulting from a small flame placed under the beam. The number of AE events in a minute and the cumulative energy released during the heating cycle provide a good measure of the overheated state of some of these materials even before a temperature increase is indicated. The measured signals varied in energy and number with the type of material, the thickness of the specimen and heat flux. Wood was particularly susceptible to acoustic emission, producing more than 1000 events/min in a solid fir board and 30/min in 13 mm thick plywood when the flame exceeded 1 kW. A gypsum board produced 16 events in a minute. An aluminum plate did not respond above the background level (0.3 events/min) even though it reached the highest temperature. The differences in cumulative energy were equally striking, with the plywood being four times more energetic than the gypsum board even though the heating period for the wood was half as long, and 30 times more energetic than the aluminum. Some critical issues which remain to be investigated before this technique can be adapted to practical fire detection are mentioned.

The international FORUM of fire research directors: A position paper on evaluation of structural fire resistance

The International FORUM of Fire Research Directors periodically takes positions on issues dealing with the direction and implementation of fire research with the potential for significant impact on safety and/or global standards and test methods. This short communication represents the FORUMs position on structural fire resistance test methods and evaluation procedures. It is proposed that the prediction of the performance of coupled building systems to the point of impending failure in a fire be established as an overriding goal for the construction and building products industries, and that research be channeled to produce the material data bases, the new instrumentation, the expanded test facilities, and the innovative analytical methods to support the changes to standards, codes and practices that are necessary to attain this goal.

Assessing Halon Alternatives for Aircraft Engine Nacelle Fire Suppression

A coaxial turbulent spray burner was built to evaluate the relative effectiveness of different chemicals for suppressing fires in a jet engine nacelle. The fire suppressant of current choice, halon 1301 (CF 3 Br), must be replaced because of its detrimental effect on the ozone layer. The alternatives being considered lack the chemical activity of CF 3 Br, so that the ability of the agents to mix into the flame convectively and to absorb heat is critical to their success. An agent delivery system was designed to inject the desired amount of material into the air upstream of fuel nozzle and to control the agent injection rate through variation of the storage pressure and the duration of time that a solenoid valve remains open. The influence of air velocity, fuel flow, and injection period on the amount of nitrogen required to extinguish a jet fuel spray flame is discussed. The effectiveness of eleven different fluorocarbons, hydrofluorocarbons, and hydrochlorofluorocarbons is compared to that of halon 1301. The alternatives required 1.7 to 2.3 times the amount (on a mass basis) of CF 3 Br to extinguish the spray flame, with HCFC-22 being the most efficient and FC-31-10 the least.