04.10 Suppression methods

04.10 EV battery fire suppression

How do firefighters put out an EV battery fire?

Due to the self-sustaining nature of thermal runaway, we've moved away from using the word 'extinguish' in relation to lithium-ion battery fires and instead prefer to discuss how we suppress & contain them.

We're going to break this page down into three parts:

Best practice methods
Challenges of EV battery pack designs for firefighting
Products coming to market

This page is best viewed on a computer screen; if using a mobile or tablet you may have to turn sideways to see scroll options for two tables.

What are the best practice methods for putting out an EV battery fire?

There is no one method to manage an EV battery fire, rather three methods used globally that have emerged as best practice; Cool, Burn, Submerge.

Each of these EV fire incident management methods are valid options for suppressing & containing an EV in thermal runaway. The Cool or Burn options do not require fire agencies to purchase or use additional tools, which may be cost prohibitive or difficult to carry.

EV battery fire suppression - cool
Use fog nozzles to knock down flames & provide cooling jets onto battery pack exterior to cool down the exothermic reaction of thermal runaway.

Pros:

Recommended by all EV manufacturers
Firefighters are 'seen' to be doing something by public

Cons:

Doesn't get water where it needs to be
Like 'putting out a kitchen fire by spraying water on the roof of a house'
Water usage may be in excess of 10,000 litres
Run off will need to be monitored & captured, particularly near waterways

Case study:

A plug-in hybrid EV was accidentally submerged in salt water at a boat ramp, with thermal runaway following removal, which was knocked down by firefighters, & secondary ignition occurring while being towed. Crews used two hose lines to cool the battery pack for an extended period. 15th May 2020, Port Moody, Canada

EV battery fire suppression - burn
Allow the lithium-ion battery pack to burn itself out, hot & fast.

Pros:

Recommended by some EV manufacturers
Burns through majority of live cells, leaving scrap metal
Removes stranded energy & secondary ignition risk

Cons:

Time to burn will depend on battery size, state of charge, ambient temperature & other factors
Air quality risks - monitoring & warnings for surrounding exposures
Public / media attention; 'why aren't firefighters DOING something?'

Case study:

An EV went into thermal runaway while fast charging. The fire department opted to let the battery burn out. It was flipped onto it's side for easier monitoring with a thermal imaging camera. Time taken to burn is unknown. 22nd April 2022, Berlin, Germany.

EV battery fire suppression - submerge
Submerge EV in a containment unit that can be filled to pack level with water.

Pros:

Contains fire spread
Manages incident relatively quickly
Firefighters are 'seen' to be doing something by public

Cons:

Containment units may not be available or in close enough proximity
Water usage may be in excess of 10,000 litres
EV may need to remain in water for days/weeks
Thermal runaway will continue underwater
Time for thermal runaway to conclude depends on battery capacity & state of charge
Water will need to be treated for disposal which can be expensive

Case study:

An EV went into thermal runaway with off-gassing, but no visible flame, while at the dealership. Fire crews organised a containment unit & the EV was submerged for several weeks. 25th March 2019, Tilburg, Netherlands.

How do you put out an EV fire submerge.png

What are the challenges of suppression using the Cool method?

There are two main challenges with firefighting an EV battery fire: position & access.

The position of the EV battery pack makes firefighting difficult:

We previously looked at how a traction battery is constructed, & how (in most EVs) it is positioned along the floor pan of an electric vehicle, between chassis rails.

If the battery pack goes into thermal runaway, the position means:

It's difficult to locate the area in the pack thermal runaway is occurring, either visually or with a thermal imaging camera (TIC)
Spraying water onto the outside of the pack to cool it often means firefighters have to be close to the vehicle & risk exposure to jet like flames

Lithium-ion battery pack underneath an electric vehicle

Electric vehicle EV HV cabling x-ray view.png

It's usually impossible to get cooling water onto the battery cells:

The construction of an EV battery pack where individual lithium-ion battery cells are contained within a module, & modules within the pack, means getting water where it needs to go to cool the cells is almost impossible.

However; we are aware of some cases where an EV has been involved in a collision, & firefighters were able to direct water into the pack where it had torn open, to directly cool the battery cells. This is safe to do & does not carry the risk of electrocution (unless the EV is connected to energised EV charging).

Cells & modules are contained within a pack, which is IP rated & essentially waterproof

What about extinguishment or suppression products?

As with all emerging industries, a range of products claiming to 'extinguish' EV battery fires are being aggressively marketed to both fire agencies & the private sector as the answer to EV battery fires.

We are often asked whether a fire agency should buy a fire blanket, cutting tool or extinguishing agent, & our answer is; no, there is no need to purchase extinguishing tools for EV battery fires.

While this response does not make us popular with those manufacturers, currently (as of 2024):

EV battery fires are rare
These tools are typically very expensive
They may be too large & heavy to be comfortably carried on a truck
Often come with no manufacturer operating procedure or training

It should also be noted that some of these products may actually increase risk to emergency responders, even when being used correctly.

Having said that, there are some scenarios in which these tools may be useful, & all considerations are outlined in the comparison table here.

EV battery fire suppression - fire blankets
Large thermal fire blanket that is placed over an EV to contain flame.

Pros:

If used in time, blanket will contain flames & stop fire spread to exposures
Can be left on EV as it's moved from scene

Cons:

~25kgs for one car-sized blanket, so must be used by two firefighters in breathing apparatus
Cannot 'extinguish' or stop thermal runaway (despite manufacturer claims!)
Thermal runaway will continue under blanket & may slow down (as opposed to the Burn method), the process
Vapour cloud (off-gassing) will continue under the blanket
More independent testing is required to ensure efficacy & safety for responders

Increased risk:

Where a blanket is lifted by wind or a person, the build up of gases under the blanket may cause a localised vapour cloud explosion
Blankets often come as single or multi use, but there are no agreed, safe decontamination procedures for multi-use blankets

For responders:

We do not consider it necessary to buy & make space on a truck for a fire blanket for the sole purpose of EV battery fire management at this time
Where blankets have been purchased by a high-risk site, fire blankets should be used with caution to avoid causing vapour cloud explosion
As most thermal runaway events occur prior to fire crew arrival, fire blankets will typically be most useful post-incident to contain a potential secondary ignition

For private sector businesses:

Sites where EVs are parked, stored or charged in normal operating conditions do not require fire blankets
Higher risk sites such as where EV or lithium-ion battery repairs, servicing or manufacturer occur may consider purchasing a fire blanket, but;
A standard operating procedure should be sought from the manufacturer or written by the site, including:
- NO staff should be trained to cover an EV in active thermal runaway due to high risk of injury or death
- Blankets should be used by attending fire crews only

EV battery fire suppression - fire extinguishers
Any portable fire extinguisher, including those specifically marketed for use on metal fires or lithium-ion battery fires.

Pros:

EV fire extinguishers may be successfully used where individual cells are in thermal runaway in an open space

Cons:

EV fire extinguishers cannot access the battery cells, which are contained within modules and a pack, which is IP rated
More independent testing is required to ensure efficacy & safety for responders

Increased risk:

EV fire extinguishers may give a false sense of security that they will extinguish a lithium-ion battery fire, putting people in close proximity to off-gassing, flames & the risk of explosion

For responders:

We are not aware of any real-world incident in which fire extinguishers have been successfully used to suppress an EV battery fire

For private sector businesses:

Sites where EVs are parked, stored or charged in normal operating conditions do not require fire extinguishers for EV battery fires, however all recommendations for normal fire protection should be followed
Higher risk sites such as where EV or lithium-ion battery repairs, servicing or manufacturer occur may consider purchasing a fire extinguisher, but;
A standard operating procedure should be sought from the manufacturer or written by the site, including:
- NO staff should be trained to extinguish an EV in active thermal runaway due to high risk of injury or death
- Extinguishers should be used by attending fire crews only

EV battery fire suppression - cutting tools
Tools that pierce, blast or punch into an EV battery pack to apply cooling water directly to the battery cells.

Pros:

Initial testing indicates thermal runaway can be controlled in minutes, due to direct application of water to cells

Cons:

No manufacturer recommends emergency responders cut or pierce into a battery pack
Tools are expensive & heavy, & may not be able to be carried on a truck
More independent testing is required to ensure efficacy & safety for responders

Increased risk:

Manufacturers do not always give reasons for not recommending cutting tools, but they are primarily due to risks of:
- Proximity of responders to jet like flame & explosion risk while using cutting tools
- Electrocution from contact with DC high voltage systems of ~400 to 800V in cars, & upwards of 1000V in buses & trucks
The use of a cutting tool on an EV battery NOT in thermal runaway will cause it to commence, therefore making an incident more complex

EV battery fire suppression - underbody spray
A 'sprinkler' type system that can be slid underneath an EV to provide cooling water directly to the battery pack.

Pros:

Provides safe systems of work for firefighters, removing the need to be in close proximity to an EV in thermal runaway
May assist to contain fire spread, depending on width of water spray

Cons:

Cooling may slow thermal runaway duration, when compared with the Burn method
Unit may be expensive & size (typically long metal tubes) may be difficult to carry on a truck

Increased risk:

No identified increased risks for responders

04.10 What is stranded energy & secondary ignition?

04.10 EV battery fire suppression

How do firefighters put out an EV battery fire?

What are the best practice methods for putting out an EV battery fire?

EV battery fire suppression - cool Use fog nozzles to knock down flames & provide cooling jets onto battery pack exterior to cool down the exothermic reaction of thermal runaway. Pros:

Recommended by all EV manufacturers

Firefighters are 'seen' to be doing something by public

Cons:

Doesn't get water where it needs to be

Like 'putting out a kitchen fire by spraying water on the roof of a house'

Water usage may be in excess of 10,000 litres

Run off will need to be monitored & captured, particularly near waterways

What are the challenges of suppression using the Cool method?

Lithium-ion battery pack underneath an electric vehicle

Cells & modules are contained within a pack, which is IP rated & essentially waterproof

What about extinguishment or suppression products?

We are often asked whether a fire agency should buy a fire blanket, cutting tool or extinguishing agent, & our answer is; no, there is no need to purchase extinguishing tools for EV battery fires.​

EV battery fire suppression - fire blankets Large thermal fire blanket that is placed over an EV to contain flame.

Pros:

​Cons:

Increased risk:

EV battery fire suppression - cool
Use fog nozzles to knock down flames & provide cooling jets onto battery pack exterior to cool down the exothermic reaction of thermal runaway.

Pros:

We are often asked whether a fire agency should buy a fire blanket, cutting tool or extinguishing agent, & our answer is; no, there is no need to purchase extinguishing tools for EV battery fires.

EV battery fire suppression - fire blankets
Large thermal fire blanket that is placed over an EV to contain flame.

Cons: