Technical Information

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Written by: Keith Norgate

Category: Technical Information

Published: 12 August 2024

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LI-ION-BATTERIES

The big concern to all fire experts right now is what is the right detection and protection that should be used for combating lithium-ion battery fires?

Currently the published knowledge on lithium-ion battery fires and the prevention thereof is still in its infancy and a vast amount of research, proven and published, still needs to be completed.  With this in mind FSIB Fire Systems would be the last place to get the correct advice, but we can pass on the knowledge we have so far.

Lithium-ion batteries are re-chargeable and have become notorious for overheating to an extent where they will self-combust. They literally transform from a standing battery to a raging fire. Lithium-ion batteries contain lithium-ions in a flammable electrolyte. They do not contain any free lithium metal.

Ways lithium-ion battery fires start:

• Internal manufacturing defects.
• Physical damage.
• Electrical abuse (overcharging, over - discharging, short circuit).
• Thermal abuse (exposure to high temperatures).

Cell failure results in a voltage drop and increasing heat release and signals the start of ‘thermal runaway’ where the fires start.

Thermal Runaway starts in a single cell before thermal propagation creates a domino effect through the adjacent cells. The thermal runaway phase exhibits increasing temperature and heat release plus venting / gassing off of flammable / toxic electrolyte.

So what fire precautions should be considered?

Containment

For small portable battery powered devices fireproof bags are available and are provided on aircraft to contain small battery fires.

As battery size increases the problems get greater, for vehicle batteries for instance the containment become problematic. Protecting the batteries from mechanical damage is their compromise.

For larger energy storage systems found in buildings fireproof rooms (90 plus minutes) should be considered possibly with air conditioning to ensure the environment is kept cool.

Fire detection

Significant visible smoke is generated once battery failure starts. Detectors sensitive to the smoke emitted by batteries may provide warning and be linked to shut down electricity, isolate the batteries and activate fire protection systems and can be used. However it is not known if this is early enough to detect the thermal run away.

Heat detection is suggested by some, but this is only giving a warning when the battery has generated the heat.

Detecting the “gassing-off period” of the battery with specially designed detectors offered by manufacturers like Xtralis appear to be the most acceptable solution on offer so far.

Detecting the impending thermal runaway and trigger shut down systems to electrically isolate the individual, or bank of, or rack of battery cells and avoiding the thermal run away turning into a full fire seems the way to go.

It is also worth noting that early detection of off gassing is most effective when the ventilation is limited / minimal, but it is often the case that air movement is used to keep batteries cool during normal charging operations. Hence, off gassing sensors need to be strategically positioned and sensitive enough to detect the first signs of off gases before they become too diluted

Fire protection

Gaseous fire extinguishing systems

No significant testing has been conducted with gaseous agents to control lithium-ion batteries and general opinion is that gas protection should be avoided for this application until further information is released.

Water mist systems, aerosol systems

As above insufficient information or testing is available for these applications

Water sprinklers

From most reports the suggested suppression method at this time is for the use of water, lots of water. FM Global has conducted tests for warehouse storage of Lithium ion batteries and has been followed by ASIB producing technical guide notes on protection of lithium ion batteries.

Conclusion

Lithium-ion batteries can develop into significant and unstoppable thermal runaway fires, so careful considered measures are required to address the hazards that these pose and the options available to manage such risks.

In all cases, a risk assessment is required to determine the nature and extent of the fire challenges and the safety measures that should be put in place.