Browse Topic: Fire prevention

Items (78)
This study investigates the suppression of lithium-ion battery (LIB) fires using composite aqueous extinguishing agents, with a 20 Ah lithium iron phosphate battery as the experimental subject. Based on the functional selection of coverage-isolation and cooling-smothering, three aqueous extinguishing agents, S-E-1, S-E-2, and S-E-3, were designed and developed using hydrocarbon surfactants. The results indicate that all three aqueous fire extinguishing agents can effectively suppress LIB fires. Through a comprehensive evaluation of extinguishing time, cooling rate during extinguishing agent release, and physical and chemical parameters of the extinguishing agents, the optimal formulation was determined to be 2% SDS (sodium dodecyl sulfate), 1% SDBS (sodium dodecyl benzene sulfonate), 3.5% CAB (cocamidopropyl betaine), 1% APG0810 (alkyl polyglycoside), 1% CDEA (coconut oil acid diethanolamine), 0.32% CH4N2O (urea), 1.5% NH4H2PO4 (ammonium dihydrogen phosphate), 0.5% C2H6O2 (glycol), 1.5% Na3PO4 (sodium phosphate), and deionised water, demonstrated the best performance. Reducing the extinguishing time to 14 seconds, a 41.7% reduction compared to pure water, and increasing the cooling rate to 0.816 °C·s^–1, which is 4.4 times that of pure water, with no reignition observed. This work contributes to the theoretical principles needed to engineer next-generation fire suppression materials for lithium-ion batteries that are both efficient and eco-friendly.
Yu, TaoZhu, ShunbingLi, KeZhang, Menglan
In recent years, with the rapid increase in the market penetration of new energy vehicles, safety issues in electric vehicles, particularly those characterized by thermal runaway of power batteries, especially fire incidents caused by mechanical abuse from underbody impacts, have become a major focus of industry attention and social concern. This paper systematically compiles key data from electric vehicle underbody collision incidents, covering core parameters such as impact location, geometric features of obstacles (shape and size), and vehicle speed during accidents. Based on this data, the study further reviews existing underbody scraping evaluation protocols both domestically and internationally, with a focused comparison of the differences in mechanical load and battery pack response between two typical test methods: horizontal underbody scraping and 3° inclined underbody scraping. The findings of this research aim to provide data support for the refinement of relevant evaluation standards and to offer theoretical foundations and practical references for automotive manufacturers in optimizing the design and validation strategies for underbody protection of battery packs.
Wang, QingguiHe, QikeLi, WenboLi, ChunLi, Xiaodong
This document defines the technical guidelines for the safe integration of Proton Exchange Membrane (PEM) Fuel Cell Systems (FCS), fuel (considered to be liquid and compressed hydrogen storage types only), fuel storage, fuel distribution and appropriate electrical systems into the aircraft. Editorial Note: Today PEM systems and fuel storage represent the most mature FCS technology and currently forms the basis for this standard. Other types of fuel cell systems and fuels (including reforming technologies and electrolyzers), may be covered by a further update to this document.
AE-7F Hydrogen and Fuel Cells
The increasing demand for safety and reliability in aerospace applications necessitates rigorous testing of aircraft components, including light units, for explosion proofness. Traditional explosion proofness tests are destructive, expensive, and time-consuming, requiring significant resources for test setups and prototypes. To address these challenges, this research presents a numerical methodology using Computational Fluid Dynamics (CFD) simulations to investigate the explosion proofness for aircraft light units. The primary motivation of this study is to establish a computational framework that supports early-stage design screening, reduces the number of physical prototypes, and enhances understanding of explosion behavior before formal qualification testing. This work contributes to advancing engineering practices in the aerospace industry by demonstrating the efficacy of CFD simulations in evaluating and enhancing the explosion proofness of light units. The proposed CFD model, implemented in ANSYS Fluent, adheres to the standards outlined in DO 160 for case setup, ensuring the accuracy and relevance of the simulation results. The methodology involves creating a simulation domain for the light unit, initially containing an air-fuel mixture with a localized high-temperature region to initiate ignition. This setup replicates the conditions of actual explosion proofness tests, providing a realistic assessment of light unit performance This CFD simulation methodology incorporates reduced chemical reaction mechanisms to model the explosion process effectively. By simplifying the chemical reactions involved, the computational load is minimized, making the simulations both accurate and feasible. This approach ensures that the CFD model can provide precise insights into the explosion dynamics while maintaining computational efficiency.
Selvaraj, SugumaranNataraja, Prabhu
This paper presents the design of a novel intelligent monitoring platform for low and medium altitudes, aiming to offer a new solution for the development of intelligent equipment operating in this airspace. Current monitoring tasks are primarily performed by fixed-wing and multi-rotor UAVs, but these platforms face significant technical bottlenecks in flight endurance and monitoring precision. This research aims to address these deficiencies. The platform is based on a small-scale unmanned airship featuring a semi-rigid, hybrid lift-body structure. Improvements were made upon the traditional ellipsoidal hull; the hull profile was optimized using a geometric superposition method, introducing an aerodynamic camber line with a maximum camber (m) of 4% to enhance aerodynamic performance at small angles of attack. In terms of its energy system, the platform is powered by a purely electric energy system composed of solar panels and batteries; solar energy is used during the day, while surplus energy is stored in the batteries for night operations, thereby effectively extending flight endurance. For intelligent monitoring, the platform integrates an intelligent recognition and positioning system based on machine vision, which is deployed on a Jetson Nano and utilizes a YOLO11 instance segmentation model. The team has experimentally proven that the platform can effectively achieve intelligent monitoring in low and medium altitude airspace. Furthermore, the structural integrity of the gondola and the aerodynamic advantages of the modified hull have also been verified via simulation analysis. This work provides a new design concept for intelligent monitoring equipment. The platform can also be applied to scenarios such as forest fire prevention, precision agriculture, and long-term ecological monitoring, offering a new solution for the design of unmanned intelligent monitoring equipment.
Song, ZiangGao, WenxuanCao, XiaochuanZheng, XingZhao, Chong
This document applies to off-road forestry work machines defined in SAE J1116 or ISO 6814.
MTC4, Forestry and Logging Equipment
India's electric 2-wheeler (E2W) market has witnessed fast growth, driven by lucrative government policies. The two-wheeler segment dominates the Indian automotive market, accounting for the largest share of total sales. Consequently, the manufacturers of 2-wheelers are developing new electric vehicles (EV) tailored for the Indian market. However, the Indian EV market has witnessed multiple fire accidents in recent years, raising safety concerns among consumers and industry stakeholders. These incidents highlight key weakness in battery thermal management systems (BTMS), particularly during charging. Most existing E2W BTMS relies on passive (natural) air cooling, which has been associated with fire incidents due to its inefficiency in heat dissipation, particularly during charging in India's high-temperature environment. Therefore, it is imperative to build thermally viable and economical BTMS for the growing E2W vehicles with fast charging capability. FEV is actively developing the thermally efficient and cost-effective BTMS solutions tailored for Indian E2Ws operating in extreme climatic conditions. The present study evaluates a novel approach of integrating heat carrier plates into the E2W with 3.6 kWh battery pack, which is analyzed under natural and forced air cooling system. The airtight battery pack is located under the floorboard region. The multiple internal heat carrier plates models are developed and integrated with aligned and staggered cell arrangement to evaluate heat dissipation and temperature uniformity with the battery pack. The study further proposes a concept of duct and fan placement for the application during forced air cooling. The simulations are performed at a high ambient temperature of 45 °C, representing a worst-case scenario in India, using charging rates of 0.2 C for natural cooling and 0.35 C for forced cooling. The results show that the aligned cell model with 4-heat carrier plates achieve superior temperature distribution across cells, with a lower average module temperature of 49.6 °C, minimal temperature gradient of 1.3°C and reduced maximum cell temperature of 50 °C, under natural cooling. In forced air-cooling mode, the split air duct model provides better cooling over the battery cover surfaces with maximum temperature of 55 °C with ΔT of 4°C. The study also presents comprehensive details of modelling approaches and outlines the scope of further research for developing thermally efficient BTMS for E2Ws.
Raut, AnkitHiremath, Vinodkumar SEmran, AshrafGarg, ShivamBerry, Sushil
This paper presents a comprehensive investigation into the mechanisms, risks, and mitigation strategies associated with thermal runaway in lithium-ion batteries used in electric vehicles (EVs). It begins by emphasizing the urgency of the issue, identifying key vulnerabilities within EV battery systems that contribute to runaway events. A multiscale, stage-wise breakdown of thermal runaway progression is provided, illustrating how physical, chemical, and thermal interactions compound during failure scenarios. The study analyzes global incident data from 2000 to 2025, revealing trends in human health impacts, vehicle damage, and public safety concerns. Particular attention is given to how battery aging, manufacturing defects, and external abuse conditions elevate the likelihood and severity of thermal runaway. Current emergency response protocols and state-of-the-art mitigation technologies are critically evaluated to identify best practices and existing gaps in safety management. A hypothesis-driven investigation explores the distinct thermal runaway risks associated with compact battery formats, supported by simulated abuse and accelerated aging validation. The paper concludes by proposing advanced cooling strategies, improved battery chemistries, and safer architectural designs, aligned with evolving industry safety standards. By bridging scientific analysis with practical engineering and regulatory insight, this work offers high-impact, actionable solutions to support the development of safer, more resilient EV battery systems and to accelerate the transition toward sustainable electric mobility.
Jain, GauravPremlal, PPathak, RahulGore, Pandurang
This document is reissued for application to helicopters. It is primarily intended to apply to the engine or engines, but it shall also apply to fire protection of lines, tanks, combustion heaters, and auxiliary powerplants (APU). Post-crash fire protection is also discussed.
S-12 Powered Lift Propulsion Committee
Author turns classroom quest into a tome for anyone who wants to engineer safer cars. A seasoned engineer with a multi-discipline background in electronics, manufacturing systems, and forensic analysis, Erbis Biscarri brought decades of experience to the topic of automotive safety in his latest work. Biscarri's book, Fires in Conventional and Electrified Vehicles: Theory, Prevention, and Analysis, published by SAE International, offers a comprehensive guide to one of the industry's most pressing challenges: vehicle fire safety. In addition to technical analysis, Biscarri said, the book helps clarify common misconceptions, especially those surrounding electric vehicle fires, by grounding the discussion in documented incident data and established technological principles.
Blanco, Sebastian
Forest fire prevention and control agencies in São Carlos, in the interior of the state of São Paulo, Brazil, will soon have help from the sky to detect fires more quickly and combat them before they grow out of control and cannot be extinguished.
This document is reissued for application to helicopters.
S-12 Powered Lift Propulsion Committee
This SAE Aerospace Recommended Practice (ARP) establishes general criteria for the installation (e.g., type, location, accessibility, stowage) and crew member training needed for portable fire extinguishers.
S-9A Safety Equipment and Survival Systems Committee
Hydrogen-electric vertical takeoff and landing (H2eVTOL) (or fuel cell-electric VTOL) aircraft technologies are poised to emerge in the next coming decades and start operating from existing heliports and new vertiports. This paper assesses how key H2eVTOL design features interact with the ground infrastructure and how facility designers can address H2eVTOL specific facility requirements–especially the supply of hydrogen to the aircraft. Vertiport design should maximize compatibility are important to facilitate the accommodation of hydrogen technologies, minimize the need for extensive capital investments, and promote safety and operational efficiency. Considerations should be given to factors such as general aircraft configuration, electric and hybrid propulsion systems, and refueling infrastructure. The definition of notional aircraft concepts representing the evolution of critical VTOL aircraft over the next coming decades can help aviation facility planners and designers understand the type of vehicles they need to account for and also evaluate the future hydrogen demand. The lack of aviation-specific standards, especially when it comes to fire prevention, might adversely impact vertiports. Strategies are proposed for mitigating the effects of hydrogen operations at space-constrained facilities.
Le Bris, GaëlNguyen, Loup-Giang
Batteries in electric vehicles can fail quickly, sometimes catching fire without much warning. Sandia National Laboratories is working to detect these failures early and provide sufficient warning time to vehicle occupants.
Safety concerns surrounding new energy vehicles have gained increasing national and social attention. Bottom impacts to power batteries are a leading cause of fires and explosions in new energy vehicles. Focusing on the safety of power battery bottom impacts, this article first proposes applying honeycomb panels to the battery’s bottom guard plate. Through the ball impact test, the effect of honeycomb panel surface material thickness on bottom protection is studied, and the mechanism of the honeycomb panel’s ball impact protection is explored. Second, the honeycomb panel and the aluminum alloy plate are structurally compounded to improve the ball impact protection ability. Finally, the optimized composite bottom guard plate is assembled on the lower box of the power battery, and the whole package ball impact experiment is successfully verified. This study serves as a reference for future research on power battery bottom impact protection and the industrial application of bottom guard plates.
Hongguang, HuangYong, ZengWeiquan, Zeng
Fires in Conventional and Electrified Vehicles: Theory, Prevention, and AnalysisR-56711/19/2024
In the ever-evolving landscape of automotive technology, fire safety remains a critical concern. From the era of steam-powered vehicles to today’s cutting-edge electric and hybrid models, understanding the risks and preventive measures for automotive fires is essential for protecting lives and assets. In Fires in Conventional and Electrified Vehicles, Erbis Biscarri, a seasoned expert with extensive experience in both automotive equipment manufacturing and major car manufacturers, presents a definitive guide on the subject. This book provides a thorough exploration of the physical phenomena leading to vehicle fires, offering in-depth analysis methods and prevention strategies tailored to both traditional internal combustion engines and the latest hybrid and electric vehicles. Organized into three key sections—Theory, Prevention, and Analysis—the book delves into the fundamental concepts of fire initiation, sustenance, and propagation, covering a wide range of vehicle systems. It examines safety risks and effective prevention strategies using industry best practices and advanced technologies. Additionally, the analysis section provides real-world case studies and expert insights into investigating and understanding automotive fires. Whether you're an automotive engineer, fire safety professional, forensic consultant, or fleet manager, Biscarri's comprehensive guide is an invaluable resource. Equip yourself with the knowledge to navigate the complexities of automotive fire safety and contribute to a safer, more resilient automotive industry. “This book will be a valuable resource for experts in vehicle fire analysis.” Aubert George, Expert in vehicle fire analysis and prevention, France.
Biscarri, Erbis Llobet
Letter from the Focus Issue Editors
Shen, RuiqingWang, Qingsheng
The lithium-ion batteries are susceptible to fires or explosions due to their extremely volatile nature. The energy-dense batteries, such as Li Ni0.8Mn0.1Co0.1 O2/Graphite(NMC811) battery that meets the consumer range demands, are most vulnerable under thermal events. A wide number of solutions are being explored to suppress or prevent battery fires. The solutions range from integrating active cooling techniques, passive heat dissipation using heat carrier pads, thermal insulating materials to prevent thermal propagation, safety vents to remove ejecta, and protection circuitry with an advanced battery management system. This paper reviews various safety solutions employed in battery packs for preventing or suppressing potential fire during any thermal runaway event. The identified safety solutions also feature distinctive methods such as using hydrogel agents, aerosol fire suppressants, and design features. Among the reviewed countermeasures, we provide a detailed analysis of the recent heat mitigation techniques that use thermal barrier pads in battery pack design. Overall, our analysis highlights the need for a multi-layered approach to battery safety, including both active and passive measures.
H, ManjunathaNambisan T M, Praveen KumarR, PavanP, Hari Prasad ReddyG M, BharathKulkarni, Mukund AravindSundaram, Saravanan
This guide is intended to promote safe designs, operations and maintenance on aircraft and ground support oxygen systems. This is also a summary of some work by the ASTM G 4 Committee related to oxygen fire investigations and design concerns to reduce the risk of an oxygen fire. There have been many recent technological advances and additional test data is available for evaluating and controlling combustion hazards in oxygen equipment. Standards that use this new information are rapidly evolving. A guide is needed to assist organizations and persons not completely familiar with this process to provide oxygen systems with minimum risks of combustion. This guide does not necessarily address all the detailed issues and provide all data that will be needed. For a complete analysis, supplemental publications need to be consulted. This guide does discuss the basics of oxygen systems fire hazards. The hazard analysis process is discussed and a simple example to explain this process. Also, this guide does not address the overall system safety issues normally evaluated in aircraft programs. This guide does provide some important background and observations about combustion in oxygen systems. Information is given describing how to accomplish a hazard analysis. Furthermore, background is provided to explain critical locations in oxygen systems that need to be evaluated and other locations that do not require hazard analysis. It is important to note that any effort that requires a comprehensive and effective hazard analysis should use the complete information in the documents referenced herein. In general, the need for a hazard analysis applies primarily to gaseous oxygen equipment at 50 psi and higher pressures. LOX equipment does have hazards concerns as well and is usually treated similarly to GOX equipment at 500 psi. It should be noted that there are other phenomena associated with LOX equipment that must be considered. An example is that LOX can combine with hydrocarbons to form a gel, which explodes under impact. On the other hand, since LOX is a very cold liquid it tends to quench most possible ignition sources that could cause promoted ignition. When examining oxygen equipment at lower pressures the primary concern is the increased ignition and fire concern with combustible non-metals.
A-10 Aircraft Oxygen Equipment Committee
Thermal runaway of lithium (Li)-ion batteries is a serious concern for engineers developing battery packs for electric vehicles, energy storage, and various other applications due to the serious consequences associated with such an event. Understanding the causes of the onset and subsequent propagation of the thermal runaway phenomenon is an area of active research. It is well known that the thermal runaway phenomenon is triggered when the heat generation rate by chemical reactions within a cell exceeds the heat dissipation rate. Thermal runaway is usually initiated in one or a group of cells due to thermal, mechanical, and electrical abuse such as elevated temperature, crushing, nail penetration, or overcharging. The rate of propagation of thermal runaway to other cells in the battery pack depends on the pack design and thermal management system. Estimating the thermal runaway propagation rate is crucial for engineering safe battery packs and for developing safety testing protocols. Since experimentally evaluating different pack designs and thermal management strategies is both expensive and time consuming, physics-based models play a vital role in the engineering of safe battery packs. In this article, we present all the necessary background information needed for developing accurate thermal runaway models based on predictive chemistry. A framework that accommodates different types of chemical reactions that need to be modeled, such as solid electrolyte interphase (SEI) layer formation and decomposition, anode-solvent and cathode-solvent interactions, electrolyte decomposition, and separator melting, is developed. Additionally, the combustion of vent gas is also modeled. A validated chemistry model is used to develop a module-level model consisting of networks of pouch cells, flow, thermal, and control components, which is then used to study the thermal runaway propagation at different coolant flow rates.
Gundlapally, SanthoshHolcomb, BradArtukovic, Dominik
This SAE Aerospace Information Report provides a general discussion on gaseous breathing oxygen and oxygen equipment for use on commercial aircraft. Other types of oxygen systems are mentioned to assist in this discussion. For detailed information on systems other than gaseous, refer to the appropriate section of AIR825.
A-10 Aircraft Oxygen Equipment Committee
Electric vehicle batteries typically require a tradeoff between safety and energy density. If the battery has high energy and power density — required for uphill driving or merging on the freeway — then there is a chance the battery can catch fire or explode in the wrong conditions. But materials that have low energy/power density, and therefore high safety, tend to have poor performance. There is no material that satisfies both.
This specification covers upholstery fabrics woven from nylon and treated for fire retardation.
AMS J Aircraft Maintenance Chemicals and Materials Committee
Hydrogen as a clean, renewable alternative to fossil fuels is part of a sustainable-energy future; however, lingering concerns about flammability have limited widespread use of hydrogen as a power source for electric vehicles. Hydrogen vehicles can refuel much more quickly and go farther without refueling than today’s electric vehicles, which use battery power. But one of the final hurdles to hydrogen power is securing a safe method for detecting hydrogen.
This SAE Aerospace Recommended Practice (ARP) establishes general criteria for the installation (e.g., type, location, accessibility, stowage) and crew member training needed for hand-held fire extinguishers.
S-9A Safety Equipment and Survival Systems Committee
Research and development work to solve an excessive noise problem created by an EV’s battery fast charger has led to advances in thermal management, heat dissipation, and reduced fire risks. D2H Advanced Technologies, a UK-based specialist engineering company, found that the noise occurred during the vehicle’s fast-charge cycles. It was caused by high pumping-power requirements for the coolant, essential to dissipate battery heat. Its OEM customer satisfied, D2H shifted its research focus directly to the thermal demands of series production lithium-ion batteries.
This Aerospace Information Report provides a general discussion on gaseous breathing oxygen and oxygen equipment for use on commercial aircraft. Other types of oxygen systems are mentioned to assist in this discussion. For detailed information on systems other than gaseous, reference the appropriate section of AIR825.
A-10 Aircraft Oxygen Equipment Committee
The purpose of this standard is to recommend minimum performance requirements to assist the specification writer in establishing a failsafe airplane interior Fluorescent light assembly design. This standard relates to the design of lamp ballasts, lampholders, fixtures, and installation of the same.
A-20C Interior Lighting
This document applies to off-road forestry work machines defined in SAE J1116 or ISO 6814.
MTC4, Forestry and Logging Equipment
The properties of a polyurethane foam are greatly influenced by the addition of graphite particles during the manufacturing process, initially used as a fire retardant. These thin solid particles perturbate the nucleation process by generating bubbles in their immediate vicinity. A large body of work has focused on foams that are reasonably homogeneous. In this work, we propose a modeling approach for inhomogeneous foams that includes membrane effects and allows pore size distributions to be accounted for. The cellular structure of the foam is obtained through a random Laguerre tessellation optimized from experimental properties. The structure of real foam samples is analyzed using X-ray computed tomography and scanning electron microscopy, followed by image processing, to create three-dimensional, digital models of the samples. The corresponding effective material parameters, including the permeability, the tortuosity and the viscous characteristic length, are subsequently computed by applying a numerical homogenization approach. All the numerical data are presented, discussed and gauged against experimental results.
NGUYEN, Cong TrucGuilleminot, JohannDetrez, FabriceLanglois, VincentBORNERT, MichelDuval, ArnaudPerrot, Camille
Texas A&M professor Jaime Grunlan and his team are developing a new flame-retardant coating using renewable, nontoxic materials readily found in nature that could provide effective fire protection for several widely used materials.
This SAE Standard details procedures for testing lead-acid SLI (starting, lighting, and ignition), heavy-duty, EV (electric vehicle), and RV (recreational vehicle) batteries, to determine the effectiveness of the battery venting system to retard the propagation of an externally ignited flame of battery gas into the interior of the battery under sustained overcharge conditions. NOTE: At this time, 2018, there is no known comparable ISO Standard.
Starter Battery Standards Committee
NASA’s Kennedy Space Center (KSC) seeks to license its Advanced Fire Retardant Materials to industry. KSC’s scientists have developed processes and know-how to impart fire retardancy to common polymers such as nylons, polyesters, and acrylics. NASA developed this technology for use in personnel protective systems for launch pad personnel engaged in hazardous materials (HAZMAT) operations. The invention provides polymer blends containing polyhydroxyamide and one or more flammable polymers. The polymer blends are flame-retardant and have improved durability and heat stability compared to the flammable polymer portion of the blends.
This document applies to off-road forestry work machines defined in SAE J1116 or ISO 6814.
MTC4, Forestry and Logging Equipment
The scope of this document is to provide a list of documents of types pertaining to the effects of oxygen on ignition and combustion of materials. Consolidating these references in one place makes it easier to find documents of this type as these references are difficult to locate.
A-10 Aircraft Oxygen Equipment Committee
The regenerative blower provides air flow through structures or systems that have relatively high flow resistance. Specifically, the regenerative blower was designed to provide a flow of ventilation gas through a spacesuit and its portable life support system (PLSS). Since the ventilation gas is primarily oxygen, fire prevention is a critical design requirement.
This document applies to off-road forestry work machines defined in SAE J1116 or ISO 6814.
MTC4, Forestry and Logging Equipment
This SAE Aerospace Recommended Practice (ARP) provides guidance for substantiating the airworthiness of aircraft engine components. Generally these components are associated with the engine control system, the system or systems that allow the engine to provide thrust or power as demanded by the pilot of the aircraft while also ensuring the engine operates within acceptable operating limits. But these components may also include hardware and systems associated with engine lubrication, engine or aircraft hydraulic or electrical systems, aircraft environmental control systems, thrust reverser control, or similar aircraft or engine propulsion system functions. This paper develops the concept of using a 26 item matrix of environmental conditions for evaluating aircraft engine component airworthiness. This approach is compatible with current practices used in the industry and has been accepted by engine certification authorities as part of engine certification programs.
E-36 Electronic Engine Controls Committee
The scope of this document is to provide a list of documents of types pertaining to the effects of oxygen on ignition and combustion of materials. Consolidating these references in one place makes it easier to find documents of this type as these references are difficult to locate.
A-10 Aircraft Oxygen Equipment Committee
The term "secondary polymer layered impregnated tile" ("SPLIT") denotes a type of ablative composite-material thermal- insulation tiles having engineered, spatially non-uniform compositions. The term "secondary" refers to the fact that each tile contains at least two polymer layers wherein endothermic reactions absorb considerable amounts of heat, thereby helping to prevent overheating of an underlying structure. These tiles were invented to afford lighter-weight alternatives to the reusable thermal-insulation materials heretofore variously used or considered for use in protecting the space shuttles and other spacecraft from intense atmospheric- entry heating. Tiles of this type could also be useful on Earth as relatively lightweight components of fire-retardant structures.
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