This study has been carried out at the request of the Federal Aviation Administration (FAA) and the United Kingdom Civil Aviation Authority (UK CAA) under the provisions of a UK CAA contract. The broad objectives of the study are to collect and analyze data relating to in-service occurrences involving fire, smoke or fumes on US registered aircraft. This involved the compilation of data into a Fire, Smoke or Fumes Occurrence (FSF) Database compiled in Microsoft Excel. The analysis compares genuine and false occurrences by source of fire, smoke, fumes or odors and consequences (diversions, overweight landings, etc.). The data has also been analyzed to derive any likely trends in rates of occurrence. These objectives have now been achieved for data collected over the period 2002 to 2011 and are addressed in this report. A further objective of the study is to analyze the data to determine the monetary impact of the occurrences and any trends in these impacts, which is also addressed in this report.
Fire tests were conducted on lithium-ion, lithium-pouch, and lithium-metal battery cells of various cathode chemistries and sizes to evaluate their failure effects. First, tests were performed with a single cell in thermal runaway. Next, a thermal runaway propagation test with five cells was conducted. Finally, a vent gas ignition test to determine the flammability of the vent gases was performed. The tests showed a large variation in the fire hazard characteristics of the thermal runaway event. The characteristics depended on cell size, chemistry, construction, and orientation. As a result of the tests, it is recommended that each battery cell be evaluated on an individual basis dependent on its specific application and operating environment.
One of the dangers of shipping lithium batteries in an aircraft is the risk of thermal runaway propagation, which can cause an uncontrollable fire in the cargo compartment. During thermal runaway, a significant quantity of hydrogen and hydrocarbons may accumulate and ignite in the shipping boxes and the free space within the cargo compartment. This can cause a pressure pulse sufficient to compromise the safety of the aircraft. With the pressure relief panels removed or the liner compromised, the compartment would no longer be able to fully contain the Halon 1301 fire extinguishing agent.
A series of tests were conducted to determine the minimum quantity of 18650-sized battery cells required to produce a flammable gas mixture that, if ignited, would be capable of producing a pressure rise that would open pressure relief panels and possibly dislodge cargo liners. A mixture of bottled battery vent gas and air was metered into a balloon at a concentration that was previously shown to maximize the pressure rise of combustion. A spark igniter located within the balloon ignited the mixture. Validation tests were conducted to determine if the pressure rise from the combustion of the bottled battery gas mixture replicated the pressure rise of the actual vented battery gases. The results showed an identical pressure rise. Depending on the state of charge, the ignition of the vent gases from a relatively small number of lithium batteries in thermal runaway created a pressure pulse that dislodged the pressure relief panels in an aircraft cargo compartment.