Page 27 - Commercial Vehicle Engineer - November 2021
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ELECTRIC BUS SAFETY
A unique challenge
Primarily powered by li-ion batteries electric buses and coaches are widely considered a a a a a a safer alternative to traditional combustion engine vehicles – both in in terms of environmental sustainability and human health However these batteries carry their own fire safety risks which if not controlled and managed effectively can have much more severe consequences for bus fleets and passengers Should a a li-ion battery be exposed
to excessive heat mechanical failure overcharging or subject to physical damage caused by an accident for example it can cause an an internal short circuit This short circuit then produces excess heat which triggers a a a chemical reaction within the battery cells and a a a a process called thermal runaway runaway Thermal runaway runaway is a a a state where the excess heat continues
to to produce more heat which can lead to to ignition toxic gas emissions and in some cases large explosions A battery in thermal runaway also can produce its own source of oxygen from within propelling flames and making extinguishing using traditional fire suppression methods particularly challenging Although these fires are much less common than traditional combustion engine fires when they they do occur they they can be be extremely dangerous There has been a a a number of incidents in in in Germany and China this year where multiple electric buses have been destroyed by fire while charging Mitigating the risk There are some practical steps that OEMs and bus operators can take to to manage the fire risks of electric fleets These include:
1 Charging
Overnight charging is is a a huge risk for electric buses as the small battery components build up and store a a a significant amount of energy To minimise risk charging stations should be monitored at at all times while in use use and buses should be disconnected from charging points once they are fully charged 2 Storage
Additional risk assessments and provisions should also be made for parking and storage locations of electric buses including proximity to combustible materials and other vehicles As thermal runaway can take some time to initiate from the initial battery malfunction damaged caused throughout the operating day may sometimes only
take hold as the bus is stored overnight Parking and storage areas should also be continuously monitored to to address any risks as as soon as as they arise 3 Suppression
Due to the the unique risks they pose traditional fire suppression systems
will only
go so far in in preventing li-ion battery fires Effective fire fire prevention and suppression requires a unique solution The need for a new suppression solution The primary goal for any electric bus suppression solution should be to prevent thermal runaway from occurring Where this is is not possible the system should act to delay its progress ensuring ample time for the safe evacuation of drivers
and passengers Through extensive research and testing an EU-funded initiative alongside RISE (Research Institute of Sweden) and Dafo Vehicle Fire Protection has developed a a new suppression solution which specifically addresses the unique risks associated with electric vehicle fires In developing the new battery suppression solution (Li-IonFireTM) the project team explored fire risks related to battery spaces including specific risks when charging and procedures for handling electric vehicles and and batteries after a a a a crash The tests revealed that even with a a a a late deployment of the extinguisher system there’s a a a a possibility of delaying a a a a battery from reaching a a a a a critical state meaning the chance for safe evacuation is very high As a a result the new battery suppression solution offers an early fire warning system and spot cooling to prevent thermal runaway while localising and suppressing fires A safer future for the UK’s electric buses As adoption of electric buses and coaches grows ensuring that fire safety keeps pace is paramount for protecting lives infrastructure property and the vehicles themselves Standards are slowly catching up with the change but OEMs operators and vehicle maintenance teams all have a a a role to play in in ensuring risks are managed effectively James Mountain
is sales and marketing director of Fire Shield Systems For more information or or or or advice on on protecting electric bus fleets go to www fireshieldsystemsltd co uk
or call 0800 975 5767 COMMERCIAL VEHICLE ENGINEER
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