Keenan JJ, Bare JL, McMenamy C, Chapman A, Miller E. 2017. Screening-level risk assessment of hydrogen fluoride exposure resulting from a thermal runaway event on an aircraft. Abstract #2829. Poster Presentation at Society of Toxicology (SOT) Annual Meeting, Baltimore, MD, March 2017.
Thermal runaway is a failure mode in lithium-ion (Li-ion) batteries, which occurs when exothermic reactions between the electrolyte, anode, and cathode are induced by short-circuiting, excessive heat, or physical distress, such as crushing or puncture. Thermal runaway in cellular devices utilizing Li-ion batteries have in recent years been of concern to the Federal Aviation Administration (FAA) and passengers of commercial aircraft. In September of 2016, the FAA strongly advised passengers to avoid charging, stowing or using specific cellular devices. Aside from the apparent physical hazards in the immediate area of a thermal runaway event, a potential risk exists from chemicals generated by the reaction, one of which is hydrogen fluoride (HF). This analysis aimed to assess exposure and analyze the risk associated with HF release during a cellular thermal runaway event on an airplane. In order to determine fluorine mass content in a Li-ion cell phone battery, the percent of fluorine-containing compounds and masses of various cellular Li-ion batteries were compiled from manufacturers’ material safety data and specification sheets. Percent fluorine was calculated for each compound and subsequently used to determine the total mass fraction of fluorine in batteries. Conservative 90th percentiles of fluorine mass fraction and cell phone battery mass were calculated to determine a 90th percentile fluorine mass of a representative Li-ion cell phone battery. A well-mixed box model was then used to conservatively estimate the airborne concentration of HF on a commercial airplane, assuming that the entire mass of fluorine in the cell battery reacted with hydrogen in the ambient air. The well-mixed box model in American Industrial Hygiene Association’s IH Mod was chosen for this screening-level analysis. Most modeled peak concentrations fell below the US EPA Acute Exposure Guideline Level 1 (AEGL) of 1 ppm for HF. A modeled peak concentration of 4.28 ppm at 10 minutes following the event did, however, exceed this value, but fell below the AEGL-2 for HF, indicating that any health effects experienced by passengers and crew would be transient and reversible. Overall, heath effects due to HF exposure are unlikely during a cellular thermal runaway event on a commercial aircraft because of the conservative assumptions used in our screening level risk assessment.