On April 10, 2023, a man rode his electric bike home from his job in Manhattan to his home in Queens, NY. He lived in a walk-up apartment with his five children. Like normal, he parked his electric bike at the bottom of the stairwell and plugged it into its charger, which was attached by an extension cord to an outlet upstairs. Some time later, the electric bike caught fire in the vestibule, and immediately traveled up the stairs. By the time he noticed, it was too late to exit by the stairwell, and he was able to retrieve three of his children and exit by a window. His 19-year-old daughter and 7-year-old son did not survive the inferno.
It is possible that this scenario could have been averted. While smoke alarms are mandated in the United States, and it is almost certain that his smoke alarm went off and warned him, there is a problem with lithium-ion battery fires and most smoke alarms.
Smoke alarms in the United States are either of the photoelectric or ionization types. Photoelectric detectors are responsive to slow-smoldering fires with 0.4 – 10.0 micron particles and light-colored white/grey smoke. Ionization smoke detectors are best at detecting fast-flaming fires with smaller particles, 0.01 – 0.4 microns and dark or black smoke.
Lithium-ion batteries burn differently. They are designed so that, when pressure builds up inside the battery prior to ignition, the packaging will burst and release a combination of hydrogen, carbon dioxide and organic compounds, none of which are detectible by either type of smoke detector. This can happen several minutes prior to an actual fire that would emit smoke, especially when the cause of thermal runaway is self-heating of the cell. And when they do ignite, they tend to emit particles that are too small for photoelectric detectors to pick up, generally between 0.01 – 0.1 microns.
So in the scenario above, it is most likely that the battery heated up during charging until self-heating of the battery occurred. This is when the energy of the battery starts to be released, not due to an internal short circuit, but due to internal chemical reactions such as the dissolution of the SEI layer at the anode and other, relatively slow reactions. The cell would likely vent, releasing the hydrogen, carbon dioxide and organic chemicals. This stage would release a chemical smell that would be a warning. But if it is downstairs, out of the living area, it may go undetected. Later, the cell would ignite, and in a burst of flames release most of the electrical energy of the cell, igniting the cell and beginning to ignite the materials around them. If the smoke detector was a photoelectric type, this fire also may go undetected. Only when the wood and other materials from the stairwell caught fire would the smoke be detectible by a photoelectric-type smoke detector. At this point, exiting through the stairwell is not an option.
Did it happen this way? It’s impossible to tell. It’s also possible that he ran over a bump, or banged against a car and did damage to the battery that caused it to explode quickly once it was plugged in. But many batteries do catch fire by self-heating, and they are designed to vent when they do. If there had been an alarm system that could detect hydrogen, carbon dioxide or the organic vapors, he might have had enough warning to kick the bike into the street, or get all of his family out safely.
For this reason, Soteria has been working with partners to develop an alarm system that is based on detecting those gases, among other early warning signals, and announced last week a request for advanced development partners. Soteria intends to launch a consumer device to retail outlets and online in 2024, but in an effort to get the devices into as many houses and garages as quickly as possible, we will also license the technology to any partner that will also develop a product based on the technology. It is our hope that someday, every major battery charger will require this to be in the charger, and in the room where large batteries are charged.
If you’d like to learn more, register to attend our upcoming informational webinar. You can also send me a LinkedIn message, or reach out to Abby Zielsdorf, who is leading the project. This is an important effort, and we are happy to share the load with any partner who can help.