04.9 Make safe & towing
When is an EV traction battery fire declared safe?
Bearing in mind the risk of reignition, many fire agencies & safety organisations are creating best practice SOPs that take into account the following make safe challenges that have arisen at past global incidents.
Clean up of battery cells & debris
Contamination & water run off
In several cases we studied, the force of impact caused individual lithium ion battery cells to be scattered across the area; remember that some vehicles may have thousands of individual cells within the battery pack. For example, some Teslas have between 4000 & 8000 cylindrical cells (known as 18650s).
A single battery cell sits between 4.2V when fully charged & 3.2V when empty. Therefore, there is a risk to emergency responders in the clean up of scattered battery cells.
Best practice for gathering scattered cells for some fire agencies includes using insulated tools & wearing protective clothing. Cells can be collected & dropped into a bucket of water for transport & storage.
Cells sit at 4.2V when fully charged & 3.2V low charge.
Consideration should be given to professional cleaning of firefighting PPC, & wash down of hoses, tools & trucks.
The amount of water used in suppression & the areas to which it ran off, should also be considered &/or reported to the relevant environmental authority.
EV traction battery fires that have occurred in enclosed spaces may need heavy duty cleaning to completely remove toxic particulates.
When can the vehicle be towed? (Always monitor for reignition!)
Once flames are suppressed & the signs of thermal runaway have ceased.
The Netherlands Institute for Safety (IFV) states the vehicle is generally considered to be safe to tow once the traction battery has remained at an ambient temperature for 15-30 minutes.
Monitoring should be done using a thermal imaging camera & listening for the hissing & popping noises that indicate thermal runaway may still be occurring.