04.10 What is EV fire reignition?
Post-incident, one of the main risks is reignition, referred to as secondary ignition
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 reignition? Once a battery cell has gone into thermal runaway, caught fire & has been suppressed, that cell typically does not catch fire again.
Other nearby cells, or even cells in other modules that were damaged in the initial incident, may then go into thermal runaway & ignite.
Reigition of an EV traction battery occurs when individual battery cells catch fire at different times.
If we imagine the two graphics below represent two seperate battery modules within the same pack, we can better understand the process of reignition.
Battery module 1
Abused battery cell
Battery module 2
Abused battery cell
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
Reignition events from the EVFS global timeline
Reducing the risk of EV fire reignition
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.