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.

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

Knowing fire temperature and soot concentration in a fire is very important in fire safety research. The fire radiant energy, a function of fire temperature and soot concentration, contributes about 40% of energy loss to the walls of the Ohio State University (OSU) fire calorimeter during the burning of large area cabin materials. This report presents a method to measure the full field of flame temperature and soot volume fraction in fire using a digital camera. The report also outlines a new procedure to simultaneously calibrate and characterize the camera’s detector using a blackbody furnace. The developed methods are implemented to measure flame temperature and soot volume fraction in a liquid-fueled steady laminar diffusion flame, impacted by the phosphorus type flame-retardant material. The flame-retardant material is found to promote soot formation and suppress soot oxidation in the fire. The increased net soot concentration cools the flame, resulting in incomplete combustion.

Hidden fire in an aircraft overhead inaccessible-area is hazardous to in-flight safety and could lead to catastrophic disaster. In this case, fire detection at the earliest stage requires an improved understanding of the heat and mass transfer in overhead areas with curved fuselage sections. In this effort, an experimental campaign was conducted at the FAA William J. Hughes Technical Center on different fire scenarios for the Boeing747-SP overhead inaccessible-area to advance knowledge on this phenomenon and provide validation data for the Fire Dynamics Simulator (FDS). Extensive work has been done recently to enable computer simulation of fire on complex geometries within this tool. Therefore, we use the experimental data obtained to perform validation of said capability. Model validation results are defined in terms of thermocouple readings measured and computed with satisfactory overall agreement.