Fire safety practices in the Shuttle and the Space Station Freedom

The Shuttle reinforces its policy of fire-preventive measures with onboard smoke detectors and Halon 1301 fire extinguishers. The forthcoming Space Station Freedom will have expanded fire protection with photoelectric smoke detectors, radiation flame detectors, and both fixed and portable carbon dioxide fire extinguishers. Many design and operational issues remain to be resolved for Freedom. In particular, the fire-suppression designs must consider the problems of gas leakage in toxic concentrations, alternative systems for single-failure redundancy, and commonality with the corresponding systems of the Freedom international partners. While physical and engineering requirements remain the primary driving forces for spacecraft fire-safety technology, there are, nevertheless, needs and opportunities for the application of microgravity combustion knowledge to improve and optimize the fire-protective systems

Numerical assessment for aircraft cargo compartment fire suppression system safety

Fire on board an aircraft cargo compartment can lead to catastrophic consequences. Therefore, fire safety is one of the most important considerations during aircraft design and certification. Conventionally, Halon-based agents were used for fire suppression in such cases. However, an international agreement under the Montreal Protocol of 1994 banned further production of Halon and several other halocarbons considered harmful to the environment. There is therefore a requirement for new suppression agents, along with suitable system design and certification. This article aims to describe the creation of a mechanism to validate a preliminary design for fire suppression systems using Computational Fluid Dynamics and provide further guidance for fire suppression experiments in aircraft cargo compartments. Investigations were performed for the surface burning fire, one of the fire testing scenarios specified in the Minimum Performance Standard, using the numerical code Fire Dynamics Simulator. This study investigated the use and performance of nitrogen, a potential replacement for Halon 1301, as an environmentally friendly agent for cargo fire suppression. Benchmark fires using the pyrolysis model and fire design model were built for the surface-burning fire scenario. Compared with experiment results, the two Computational Fluid Dynamics models captured the suppression process with high accuracy and displayed similar temperature and gas concentration profiles. Fire consequences in response to system uncertainties were studied using fire curves with various fire growth rates. The results suggested that using nitrogen as a fire suppression agent could achieve a lower post-suppression temperature compared to a Halon 1301-based system. It can therefore be considered as a potential candidate for aircraft cargo fire suppression. Such work will feed directly into system safety assessments during the early design stages, where analyses must precede testing. Future work proposed for the application of this model can be extended to other fire scenarios such as buildings, shipping, and surface transport vehicles

Development and validation of a two-phase computational model for an alternative fire suppression agent

[ES] Halon1301 se ha utilizado como agente de extinción de incendios en sistemas activos de extinción de incendios en motores de aviones, APU (Unidad de potencia auxiliar) y protección contra incendios de carga durante más de 50 años. En 1987, una investigación realizada por el Protocolo de Montreal muestra que Halon está dañando el medio ambiente debido a sus propiedades que agotan el ozono. Por lo tanto, el uso de gases de halón ha sido prohibido en la industria por el protocolo de Montreal (1994) y Kyoto (1998). Por lo tanto, es el reemplazo de gases de halón lo que es más ecológico. Entre estas alternativas, Novec-1230 es una alternativa sostenible que funciona de manera rápida, limpia y eficiente. El sistema de extinción de incendios requiere que se diluya una concentración específica del agente de extinción de incendios (4-6% para Novec-1230 y 5% para Halon) en el aire para extinguir el fuego. El problema de cambiar la fase de la niebla rápidamente despresurizada de un sistema de extinción de incendios es un tema de gran interés debido al efecto del modelado de estos fenómenos en una simulación exitosa para diseñar estas modificaciones. Debido a la gran diferencia de presiones entre el recipiente y el ambiente, se espera que la descarga a través de la boquilla sea crítica. En este informe, se utilizan dos agentes de supresión de incendios alternativos diferentes y dos boquillas: agua y Novec1230. El objetivo principal de este proyecto es desarrollar un nuevo modelo de subcuadrícula para un U-RANS CFD Euleriano-Euleriano de dos fases que pueda usarse para reducir el costo computacional y aumentar la precisión de los enfoques tradicionales basados en Eulerian-Lagrangian. Estos dos enfoques se realizan con el software comercial CFD (ANSYS Fluent). Como validación, los rendimientos de pulverización como la forma de pulverización, el ángulo del cono de pulverización se comparan con los resultados experimentales.[EN] Halon1301 has been used as a fire suppression agent in active fire extinction systems in aircraft engines, APU (Auxiliary Power Unit) and cargo fire protection for more than 50 years. In 1987, a research carried out by the Montreal Protocol shows that Halon is damaging the environment because of its ozone-depleting properties. Therefore, the use of Halon gases has been banned in the industry by the Montreal (1994) and Kyoto (1998) protocol. So, it is indeed to find replacement of halon gases which is more eco friendly. Among these alternatives, Novec-1230 is a sustainable alternative that works quickly, cleanly and efficiently. The fire suppression system requires a specific concentration of the fire suppression agent (4-6 % for Novec-1230 and 5% for Halon) to be diluted in the air to extinguish the fire. The problem of changing the phase of the rapidly depressurized mist of a fire suppression system is a topic of high interest due to the effect of the modelling of these phenomena in a successful simulation to design these modifications. Due to the high difference of pressures between the container and the ambient, the discharge through the nozzle is expected to be critical. In this report, two different alternative fire suppression agents and two nozzles are used - Water and Novec1230. The main goal of this project is to develop a new sub-grid model for a two-phase Eulerian-Eulerian CFD U-RANS that can be used to reduce the computational cost and increase the accuracy of traditional approaches based on Eulerian-Lagrangian. These two approaches are performed with CFD commercial software (ANSYS Fluent). As validation, spray performances such as spray shape, spray cone angle are compared with experimental results.Shaparia, NR. (2020). Development and validation of a two-phase computational model for an alternative fire suppression agent. Universitat Politècnia de València. http://hdl.handle.net/10251/157474TFG

Fire suppression in human-crew spacecraft

Fire extinguishment agents range from water and foam in early-design spacecraft (Halon 1301 in the present Shuttle) to carbon dioxide proposed for the Space Station Freedom. The major challenge to spacecraft fire extinguishment design and operations is from the micro-gravity environment, which minimizes natural convection and profoundly influences combustion and extinguishing agent effectiveness, dispersal, and post-fire cleanup. Discussed here are extinguishment in microgravity, fire-suppression problems anticipated in future spacecraft, and research needs and opportunities

Evaluation of VERDAGENT\uae Against the FAA Minimum Performance Standard for Aircraft Cargo Compartment Halon Replacement Fire Suppression Systems

Suitable alternatives to Halon 1301 are being sought throughout the aviation industry as a result of a worldwide agreement to ban the production and use of Halon 1301 due to the detrimental effects to the atmosphere. Fire extinguishing agents proposed for use in transport category airplane cargo compartments must demonstrate effective firefighting performance against the types of fires likely to occur in airplane cargo compartments. The Federal Aviation Administration (FAA) developed a minimum performance standard (MPS) evaluation method to compare the efficacy of any proposed agent against the known performance of Halon 1301. In this study the FAA Technical Center (FAATC) Fire Safety Branch evaluated VERDAGENT\uae, a potential fire suppression agent, in the FAATC Full Scale Fire Test Facility. Tests were performed according to procedures outlined in the MPS. VERDAGENT\uae is a blend of two components \u2013 carbon dioxide and 2-bromo-3,3,3-trifluoroprop-1-ene (i.e., 2-BTP, commonly called Halotron BrX). The MPS was originally designed considering single component agents similar to Halon 1301. Evaluation of a multicomponent agent required supplementary tests to investigate component separation and uniformity of dispersion throughout the cargo compartment. An additional challenge fire test, not within the scope of the MPS, was also performed. This fire load consisted of lithium-ion batteries and a combination of ordinary combustible materials and flammable liquids. VERDAGENT\uae demonstrated successful performance in the MPS. Component separation was not observed, and the agent was found to disperse uniformly in the cargo compartment. The agent also performed effectively against the additional challenge fire test. The results summarize that VERDAGENT\uae met the requirements of the MPS for aircraft cargo compartment Halon replacement fire suppression systems

Performance evaluation of nitrogen for fire safety application in aircraft

Fire suppression is an important safety certification requirement for aircraft as it is for all safety critical systems. Risk analyses are required at the design and certification stages to determine the probabilities and means of mitigating such risks. [18] shows an approach for spacecraft, [19] for passenger ships and [30] for reactors. An important analysis tool for aircraft is the Zonal Analysis process [31]. Such analyses include investigation of means of fire suppression for which the use of Halon 1301 was a popular choice. The production of Halon and several halocarbons were banned under the Montreal Protocol in 1994, which necessitates an investigation for use of environmental-friendly agents for this application. The primary objective of this paper is to determine the ‘design concentration’1 of nitrogen required for fire suppression. Computational Fluid Dynamics (CFD), in combination with experimental verification is described in this paper. The air flow rate in the cup-burner model was varied between 10 L/min and 40 L/min for a low-speed numerical model and was validated against the BS ISO 14520 cup burner test [1] to determine the extinguishing concentration of nitrogen. The study revealed that the design concentration of nitrogen was 34% (14% oxygen concentration). Further investigation suggested that at low air flow rates (10L/min and 20 L/min case), distortions produced in the flow led to erroneous measurement of oxygen concentration in experiments. The fire suppression model was extended to an n-heptane pool fire in a large enclosure. The recorded design concentration was approximately 39% additional nitrogen corresponding to 13% oxygen concentration by volume. It was observed that the weight of nitrogen required increased by 7.5 times compared to Halon 1301 use for this model. Future work can be explored in aircraft cargo and engine bay fire safety systems through Minimum Performance Standard (MPS) testing and simulations with nitrogen as the agent. Such work will feed directly into system safety assessments during the early design stages, where analyses must precede testing

Cargo compartment fire extinguishing system

In all large passenger transport airplanes, halon fire bottles are used to extinguish fire in the cargo compartments. Halon as a fire-extinguishing agent, contributes to the destruction of stratospheric ozone in the atmosphere and it is banned in many countries. FAA considers halon 1301 as an effective firefighting agent due to its low toxicity and noncorrosive properties but because it damages the ozone layer, it has been phased out of production. However, it is still widely used on commercial aircraft until a suitable replacement is found. In this paper we will present an alternative approach to using halon 1301 as a fire fighting paradigm. In the proposed method, nitrogen is first extracted from the atmosphere by using the onboard air separator module it is then cooled, and pressurized into the cargo compartments to suppress any fire. Several methodologies can be used to increase the flow rate from the air separator module, to extinguish fire in cargo compartment

Fire behavior and risk analysis in spacecraft

Practical risk management for present and future spacecraft, including space stations, involves the optimization of residual risks balanced by the spacecraft operational, technological, and economic limitations. Spacecraft fire safety is approached through three strategies, in order of risk: (1) control of fire-causing elements, through exclusion of flammable materials for example; (2) response to incipient fires through detection and alarm; and (3) recovery of normal conditions through extinguishment and cleanup. Present understanding of combustion in low gravity is that, compared to normal gravity behavior, fire hazards may be reduced by the absence of buoyant gas flows yet at the same time increased by ventilation flows and hot particle expulsion. This paper discusses the application of low-gravity combustion knowledge and appropriate aircraft analogies to fire detection, fire fighting, and fire-safety decisions for eventual fire-risk management and optimization in spacecraft

Flow of nitrogen-pressurized Halon 1301 in fire extinguishing systems

Halon 1301 which is a halocarbon fire extinguishing agent (CBrF3) used by the U.S. Army for vehicle fire suppression is discussed. Halon 1301 is discharged under nitrogen pressure, and the Halon-nitrogen mixture is a two phase, two component mixture that obeys compressible fluid laws and exhibits choking effects. A computer model was developed to analyze the discharge of Halon and nitrogen from a storage bottle through pipes and nozzles. The model agrees well with data from Halon 1301 discharge tests. The discharge time depends mainly on nozzle area and pipe volume, for given initial conditions. Graphs were developed for estimating discharge times. A nozzle employing multiple concentric converging/diverging nozzles was developed which gave hemispherical coverage