However, like all technologies, lithium-ion batteries have trade-offs compared to their benefits. Under certain circumstances, detailed later in the case study, they can experience a phenomenon called thermal runaway, an uncontrollable, self-heating state. Thermal runaway can lead to battery swelling, battery venting, smoke, and fire, and even explosion. ⁵

The risk of thermal runaway on aircraft is rare, but nonetheless serious. Every day, over 2.9 million people fly in and out of U.S. airports, with an estimated 5,400 aircraft in the sky at peak operating times. ¹ As technologies utilizing lithium-ion batteries are becoming increasingly common and more universally carried by individuals, it is important to ask whether the risk of thermal runaway onboard planes is increasing, and how to best prevent thermal runaway from causing harm.

Thermal runaway in lithium-ion batteries is not like a common fuel fire because a lithium-ion battery in thermal runaway creates its own oxygen as it burns. Therefore, lithium-ion battery fires cannot be suffocated by blankets or fire extinguishers, and the heat is so extreme it immediately vaporizes any water that might be used for extinguishing. Fires onboard commercial aircraft can cause danger to people, the aircraft itself, or spread to other lithium-ion powered devices. Therefore, the best thing to do if a lithium-ion battery experiences thermal runaway is to contain it quickly.  

Fire containment products are intended to contain a single thermal runaway event on an aircraft but are not able to completely extinguish the device that caught fire. The containment products are portable, designed to be user-friendly, and can be carried easily on all consumer aircraft. Currently, fire containment products are not required to be tested to any Federal Aviation Administration guidelines, though some manufacturers use marketing such as “FAA certified materials” or “tested to FAA standards” to describe their products.

ULSE worked with a group of airline professionals from industry, government, and other areas to develop a safety standard that provides safety requirements for fire containment products. This technical committee, formed in 2018, addressed the lack of standardization for these fire containment products in the development of UL 5800, the Standard for Safety for Battery Fire Containment Products. This standard establishes testing, performance, and marking criteria to evaluate fire containment products intended to safely contain consumer portable electronic devices experiencing thermal runaway and minimize the fire’s potential impact during flight. 

The TC was challenged with creating a standard that can be used to test products designed specifically for commercial aircraft, for a wide variety of electronic devices that passengers and crew may bring on board. Additionally, when considering what tests to include in the standard, the TC discussed the variable nature of batteries, thermal runaway intensity, and physical results of various devices experiencing thermal runaway.

The standard describes tests for the fire containment of four Watt-hour capacity classes of lithium-ion batteries undergoing thermal runaway. The four classes contain increasingly higher number of battery cells that correspond to the intended containment rating of the product, from small batteries (≤60Wh) to much larger batteries (161≤300Wh).

The standard includes performance ratings based on whether any smoke, shrapnel, sparks, and flames exit the fire containment product during the test. If all hazards are completely contained, then the product shall be certified to “Level 1,” and if smoke were released, the product could be certified to “Level 2.” Additionally, if there are components of the product that are intumescent (substances that swell when exposed to heat), and change their chemical composition due to aging, these materials must be tested to an Environmental Aging Test as described in another standard, UL 1479, Fire Tests of Penetration Firestops. Surface temperatures of various components of the fire containment products must be measured during tests, with different temperatures being allowable based on the component of the containment product and the composition of that individual component (metallic or nonmetallic). 

UL standards are living documents and can be updated by the technical committee when necessary. For instance, in 2024, the technical committee considered revisions to UL 5800 for circumstances in which water is the suppression agent in the product. They also reviewed the temperature test requirements when markings on the product indicate the use of gloves, which impacts the safe-handling temperature.

As of 2024, there are two products on the market that are certified to UL 5800. Encouraging fire containment device manufacturers to adopt UL 5800 is critical in ensuring travelers are as safe as possible despite the inherent risks of thermal runaway. In addition, we as the public need to be more aware of the risks of thermal runaway and take steps to ensure our devices can be quickly contained in the unlikely event of a safety risk.