04.10 What is EV fire reignition?
Post-incident, there is a risk of reignition, called secondary ignition, which is caused by stranded energy
Once an EV traction battery fire has been suppressed, the focus for emergency & secondary responders turns to the safe removal of the vehicle from the scene. While doing this, the risk of secondary ignition should always be considered.
So, what is secondary ignition? Once a battery cell has gone into thermal runaway & ignited, it is usually completely destroyed & cannot ignite again.
However, other nearby cells that were heat impacted by the fire - but not burnt - may go into thermal runaway at a later time.
These cells are called stranded energy & all responders should be aware of the risk it poses post-incident.
To explain stranded energy & secondary ignition, we've created this short video showing a burnt e-scooter battery our team were given.
Even though it had been submerged in water for 3 months, one of the cells still contained stranded energy!
What does the research tell us about secondary ignition?
Our research found 13% of the vehicles we studied reignited following initial suppression, with two reports stating that the vehicle reignited 'multiple times' over a period of several hours.
In five cases, the vehicle reignited while on a tow truck & in two cases, tow truck drivers suffered minor injuries. Additionally, one vehicle had 4 seperate reignition events & another reignited 68 days after the initial incident.
4 x seperate ignition events within 48 hours
Reignition case study 1
EV ignited following high speed collision, was suppressed, but reignited
Vehicle was loaded onto tow truck where it again reignited & was suppressed
Reignition & suppression occurred again after vehicle was placed in storage yard
Reignition case study 2
2 x ignition events 68 days apart
EV was damaged in a home garage fire on 8th February 2019 (fire cause unknown)
On 17th April 2019 it was transported to a repair shop & reignited within 3 hours
Also be aware of delayed ignition!
Very rarely, an EV involved in an incident may go into thermal runaway days or weeks afterwards, even though there was no fire during the initial incident.
In June 2022, the Sacramento Fire Department (USA) attended an EV in a salvage yard that had gone into thermal runaway. The EV had been involved in a collision 3 weeks earlier, with no fire at the time of collision.
All images: Sacramento Fire Department
How to reduce the risk of EV battery fire secondary ignition
Best practice for some international fire agencies is to allow the traction battery to completely burn out, while protecting exposures.
While this may be feasible in some circumstances, for the majority of Australian cities & towns, closing a road & allocating firefighting resources to an incident that could last several hours may not be possible.
Therefore, for vehicles where a traction battery is partially burnt & suppressed, SOPs can include measures such as monitoring the battery for a period of time with a thermal imaging camera & listening for audible signs of thermal runaway - popping or hissing noises - prior to releasing the vehicle for towing.