Lithium-ion batteries have earned a fair share of notoriety of late, even though it is the technology of choice among manufacturers of EVs, including battery electric school buses (BESBs).
Lithium-ion batteries, a general term for batteries classified by their cathode chemistry, have been linked to numerous fires because of their tendency to spontaneously combust if damaged or stored improperly, burn hotter than other fires, defy attempts to extinguish it with water due to stranded energy in damaged batteries, and reignite after a fire has been extinguished because stranded energy morphs into runaway energy.
Bill Jolbert, the sales director for vehicle systems at school bus fire suppression system manufacturer Amerex, said lithium-ion battery fires can be “very dangerous” because of the way the batteries are normally configured.
“They normally consist of large packs that contain many individual cells,” he explained. “Failure of one of those cells will very rapidly spread to the surrounding cells until all the batteries in the pack are in thermal runaway. The batteries also emit explosive hydrogen gases prior to and during thermal runaway which accelerates the fire very rapidly.”
Jolbert noted that Amerex’s solution for lithium-ion battery fires is a combination of early warning detection for the lithium-ion battery packs and a fire suppression system for the electric motors so that if a thermal event occurs in the motor, it will not spread to the battery.
Jolbert explained that for an internal combustion engine (ICE) powered school bus, Amerex would use heat detection to warn of a thermal event and suppress the hazard areas.
“With EV [school] buses we utilize an early warning detection system monitoring the battery packs to detect the off gas that occurs prior to thermal runaway [fire] to provide minutes to hours of advanced warning that thermal runaway is about to occur,” Jolbert said, adding that the minutes of advanced warning are critical for the driver to get to a safe place and evacuate all passengers off the bus.
“Lithium-ion batteries are their own energy source burning from the inside out and there is no known fire suppression agent that will completely extinguish these fires,” Jolbert added. “Many suppression agents will suppress the fire and temporarily put out the fire, but it will come back again and again. Water can be used on these types of fires but will require the fire department to stand by as the fire will continue to reignite until the energy is depleted.”
Jolbert’s point was recently illustrated last month, when a Tesla spontaneously combusted while sitting in a wrecking yard. It had been involved in a collision three weeks prior.
“Crews knocked the fire down, but the car kept reigniting and off-gassing in the battery compartment,” according to a June 11 Facebook post by the Sacramento Metropolitan Fire District, which had no previous experience handling battery fires. “It took a lot of time, water and thinking outside the box to extinguish the fire for good.” A news article estimated 4,500 gallons of water was needed to finally douse the flames after the vehicle was submerged in a freshly dug water pit to cool down the battery.
This is why Jolbert said an early warning detection system is critical for student safety in the event of a lithium-Ion battery fire.
“Having minutes of advanced warning allows the driver to get the bus to a safe location and the students off,” Jolbert said. “This is even more critical for special needs buses where evacuation can take considerably longer.”
Read more on steps the industry is taking to mitigate thermal events in battery-electric school buses in the July edition of School Transportation News magazine.
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