A method and criterion are described to assess the no-effect level of a constituent change on the fire performance of aircraft cabin material or construction. A constituent may be a thermosetting resin, coating, composite, adhesive, potting compound, film, fabric, elastomer, rubber, or thermoplastic. This can be used in the construction of a cabin material whose heat of combustion can be reliably measured using a 1-10 milligram sample in American Society for Testing and Materials (ASTM) D7309-21, Standard Test Method for Determining Flammability Characteristics of Plastics and Other Solid Materials Using an MCC. Bench-scale fire testing as per 14 Code of Federal Regulations (CFR) § 25.853 (Compartment Interiors, 2020) was conducted on several dozen cabin materials with changed constituents. Results showed that the relative difference in the microscale Fire Growth Capacity (FGC) of the certified and changed constituent in ASTM D7309-21 must be less than 0.3 (30%) to have no significant effect on the fire performance of the cabin material.

In February 2022, a package containing 140 lithium-ion pouch cells caught fire on a conveyor belt in a sort facility of an all-cargo airline. One of the packages in the shipment was sent to the Federal Aviation Administration’s (FAA) William J. Hughes Technical Center for hazard evaluation. Specialized cell analysis equipment was used to determine the state of charge (SOC) of the cells in the package. The measurements revealed that the cells were approximately at a 70% SOC, exceeding the maximum allowable shipping limit of a 30% SOC for the transport of cells and batteries classified as “UN3480, Lithium-ion batteries (including lithium-ion polymer batteries)”.

It was hypothesized that the fire in this incident started when the terminals of two cells packaged together made contact, causing the cells to short circuit, overheat, and enter thermal runaway. Testing was conducted to validate this hypothesis and to evaluate the fire risk of these cells at various SOCs. Key findings include:

• The cells tested at a higher SOC present a much higher fire risk compared to cells tested at or below a 30% SOC. This was consistent with previous FAA studies.
• The as-delivered 70% SOC cells went into thermal runaway when short-circuiting the cell terminals. The resulting temperature was high enough to propagate to nearby cells despite the surrounding packaging. This suggests that the original cell fire may have started when cell terminals made contact in the original package.
• A spark igniter ignited the gases released from the tested cells during thermal runaway. This suggests that a spark created during thermal runaway could have helped ignite the original package fire, as the ignition of cell gases would have produced a significant flame

There are many types of commercially available fire extinguishing agents used for a wide range of applications. The specific extinguishing agent used for a given application depends on the fire threat and design criteria. For class-C cargo compartments on aircraft, a gaseous flooding agent is used. Halon 1301 is currently the sole extinguishing agent being used in class-C aircraft cargo compartments. It requires a replacement due to its harm to the environment.

The fire threat within cargo compartments is changing compared to the threat that existed when aircraft class-C cargo compartment requirements were first established. The quantity of lithium batteries being shipped in cargo compartments is increasing each year. Lithium batteries can spontaneously catch fire or undergo thermal runaway where they release a significant quantity of flammable gas composed of hydrogen, carbon monoxide and hydrocarbons.

The objective of this study was to evaluate the effectiveness of Halon 1301 and some of its potential replacements against several flammable gases including lithium battery thermal runaway gases.

The United Nations (UN) Subcommittee of Experts on the Transport of Dangerous Goods (SCOE TDG) approves proper shipping names (PSN) and assigns each PSN with a four-digit UN number. Currently, two UN numbers have been assigned to lithium batteries as either UN 3480, Lithium ion batteries (including lithium ion polymer batteries) or UN 3090, Lithium metal batteries (including lithium alloy batteries). This research seeks to support the UN SCOE TDG establish a more performancebased approach to classifying the various types of lithium-ion batteries for transportation. Performance based classifications will support a better understanding of the risks of transporting lithium batteries and promote the industry in further developing safer batteries. A proposed standardized test method was used to assess the combustion hazard from a lithium-ion battery that has undergone thermal runaway. Lithium cobalt oxide pouch cells (3.7 V, 4.8 Ah) and cylindrical cells (3.7 V, 2.6 Ah) were tested at various states of charge (SOCs) and heating rates. The cells were individually heated to induce thermal runaway inside of a pressure vessel, resulting in a venting of gases. The vent gases were analyzed for their constituent’s volume, overall gas volume, and combustion energy. Key findings are as follows:

• The vent gas volume and combustion energy increased linearly with SOC for the pouch and cylindrical cells.
• The top three constituents as a percentage of the vent gas by volume across all SOCs and heating rates for the pouch and cylindrical cells were carbon dioxide, hydrogen, and carbon monoxide
• The vent gas volume and combustion energy increased with the heating rate for the pouch and cylindrical cells.
• When comparing cells heated at 20°C/min to cells heated at 5°C/min, across the tested SOCs, the pouch cells released an average of 14.1% more vent gas and had an average of 34.4% greater combustion energy, the cylindrical released an average of 7.2% more vent gas and had an average of 13.0% greater combustion energy.

Lithium batteries have been shipped aboard aircraft with existing United Nations (UN) classification numbers for many years. Although the UN classifies lithium batteries as dangerous goods, current UN numbers for lithium batteries do not indicate what level of hazard each individual shipment may pose. Lithium batteries can exhibit varied temperature rise and propagation characteristics when heated to thermal runaway. Therefore, This study was conducted to characterize the propagation of cylindrical cells and pouch cells at various states-of-charge (SoCs) to determine or verify key test factors that should be considered for development of a lithium battery propagation test.

Six cells were placed in line with each other (denoted cell # 1 through cell #6) in an insulated box, and thermal runaway was initiated in cell #1. Once thermal runaway initiated, power to the heater was cut off and propagation characteristics were recorded. Key findings included:

• The onset temperature of thermal runaway for the pouch cells depended on SoC. For example: A test at 20% SoC showed a thermal runaway onset temperature 53 °C to 83 °C higher than tests at 100% SoC.
• Pouch cells propagated faster than cylindrical cells.
• In the test at 20% SoC, the temperature of pouch cell #6 was as high as 108°C when pouch cell #1 went into thermal runaway and in the test at 100% SoC, pouch cell #6 was only 36.5 °C when pouch cell #1 went into thermal runaway. In other words, at a fixed heat rate, more time was required for cells at a lower SoC to enter thermal runaway. This indicated the need for more than six cells because too much heat was transferred to the system before propagation began.
• It was observed that the mass loss of each individual cell was fairly constant with slightly higher mass loss in the first cell.
• Cell voltage was a usable metric to pinpoint thermal runaway in the pouch cells but behaved erratically in the cylindrical