Battery fires require special measures – suffocation by oxygen deprivation or simple extinguishing with water is not possible. Fire blankets made of technical textiles are being used more and more frequently. Most often, these are fiberglass fabric with silicone coating.
Since there are no standards or minimum requirements, the market is confusing. The manufacturers promise partly very high temperature resistance and reusability. But which statements are realistic? We investigated this question together with STFI, the Saxon Textile Research Institute. Read the results in our fire blanket comparison test.
Definition: What is a fire containment blanket?
A fire blanket is a special fire blanket made of fireproof material, usually fiberglass fabric. It is suitable for use in non extinguishable battery fires, e.g. in e-cars, because it can withstand particularly hot temperatures. The fire containment blanket can reliably keep a fire under the blanket and protect the surrounding area for a long period of time.
How does a fire blanket work and how, in contrast, does a fire containment blanket work?
The use of extinguishing blankets for vehicle fires is already an everyday occurrence for many fire departments. The fire blanket is pulled by two firefighters over a burning conventionally powered vehicle and usually smothers the fire within a very short time.
The situation is different for fires involving e-cars. A battery can burn for several hours. The blanket acts as a fire barrier, protecting the surroundings from heat, smoke and, in the case of exploding battery cells, from flying parts.
A fire containment blanket is therefore suitable for containing a fire. This is because it keeps the high temperatures away from the environment and cuts off the oxygen supply. When placed over the burning object, it reduces smoke development within seconds and prevents flames from spreading to the surrounding area. Conventionally burning parts are extinguished by the lack of oxygen and the battery can burn under the ceiling without major danger.
Background: Why is it so difficult to fight a battery fire?
Dealing with electric cars is a special challenge for firefighters. This is because the energy storage units installed in the vehicle harbor a certain fire risk – after an accident, due to charging or design errors, or due to high temperatures. And even for up to 72 hours!
How does a battery burn?
A rechargeable battery contains many small lithium-ion cells. If one cell catches fire, the heat ignites the next cell. A chain reaction begins, the so-called “thermal runaway”. This chain reaction is difficult to stop. The battery would have to be cooled below approx. 70 °C. Difficult, for example, when it is installed in a car and not easily accessible for cooling measures.
Why can’t you smother a battery fire?
The oxygen required for a fire is already contained in the battery; it is released as part of the fire process. So it is ineffective to cut off a burning battery from the oxygen supply, the battery will continue to burn. Caution: Conventional burning parts can very well be extinguished by oxygen deprivation. Only the battery burns – and may reignite surrounding objects.
How does a battery fire react to water?
As part of the ALBERO project, the handling of alternative propulsion vehicles on ferries was considered. This involved investigating whether water from sprinkler systems could contain an accumulator fire. Result: No, the opposite is the case. The water actually fuels the fire.
Water can be used as a coolant to bring the temperature of the battery below 70 °C and thus interrupt the “thermal runaway”. However, considerable quantities are required for this. Tesla, for example, says that to extinguish a fire in its vehicles requires about 12,000 L of firefighting water.
What is the environmental impact of a battery fire?
Every fire releases pollutants in large quantities. If a battery burns, chemicals are also released into the environment.
What other new methods are being used for battery fires and how should they be evaluated?
Container for dipping the vehicle
A container is filled with water and the vehicle is sunk into it. Disadvantages: high cost and total loss of the vehicle.
Extinguishing lance
A lance is driven into the accumulator with great force and water is selectively applied through it. Disadvantages: Precise placement of the lance is difficult, often the battery is not easily accessible.
Plastic bag with water filling
With the help of a crane, the vehicle is hoisted into a kind of giant Ikea bag. Up to the height of the battery is filled with water. Disadvantages: high effort due to crane and large water demand, system is complicated, high price and can be used only once.
Comparison – this is how well (or poorly) different fire blankets cope with heat
The most important question is how the heat affects the structure of the fire blanket. Does the blanket remain flexible or does it become hard and stiff? Flexibility is the basic prerequisite for manageability. A stiff fire blanket is brittle and therefore no longer reliably tight. It does not pull off the vehicle smoothly, nor is it foldable, stowable, or could be reused.
This is how it was tested
The STFI – Saxon Textile Research Institute examined tissue samples from three products.
- Acetech “Ace Blanket” Fire Blanket
(Manufacturer’s specification: temperature stable up to 1,300 °C, 50x reusable) - Leader Stop fire blanket
(Manufacturer’s specification: temperature stable up to 1,000 °C, no specification on reusability) - VLITEX Fire Blanket Premium M
(Manufacturer’s specification: temperature stable for short periods up to 1,300 °C, reusable depending on fire load)
The samples were exposed to temperatures that can occur during a battery fire. In two tests, the fabric was heated to 750 °C for 15 and 30 minutes respectively.
Extinguishing blankets comparison test – the test results in detail
For the suitability and reusability of the fire blanket it is important that it changes its structure as little as possible on contact with fire. A simple bend test shows whether the fire blanket remains stable and flexible.
Acetec – valid alternative, but buckling test not successful
Both samples of the “Ace Blanket” break during the bend test after heat treatment. There is no residual strength at all. Except for small remnants, the coating is completely burned.
Acetec sample I
Buckling test after 15 minutes of heat treatment at 750 °C
Acetec sample II
Buckling test after 30 minutes of heat treatment at 750 °C
Leader – fire retardant – unfortunately without temperature resistance
The Leader Stop also does not withstand the temperatures; both specimens break during the buckling test after heat treatment. There is no residual strength at all.
Leader sample I
Buckling test after 15 minutes of heat treatment at 750 °C
Leader sample II
Buckling test after 30 minutes of heat treatment at 750 °C
VLITEX – rightly certified for use in battery fires
The samples of VLITEX fire blanket do not break during the buckling test, the fabric shows sufficiently good strength even after heat treatment.
VLITEX Sample I
Buckling test after 15 minutes of heat treatment at 750 °C
VLITEX sample II
Buckling test after 30 minutes of heat treatment at 750 °C
Details and data tables of the fire blanket comparison test can be requested from us.
Conclusion
The VLITEX Premium M fire blanket is the only one in this fire blanket comparison test that actually survives the heat treatment at 750 °C. The other two extinguishing blankets tested already lose their strength and, above all, their flexibility at just 750 °C – although battery fires usually get much hotter.
Contrary to manufacturers’ claims, Leader and Acetec extinguishing blankets are not recommended for fighting battery fires according to these test results. The material becomes so stiff that it breaks even when simply bent or folded.
What does that mean in day-to-day firefighting? A brittle, stiff fire blanket is difficult to remove from the fire object without damage. Then fold and pack the blanket is almost impossible. This makes transport problematic, and multiple uses are out of the question.
Thus, at least on the basis of this test, only the VLITEX Premium M remains suitable for fire fighting and can be used several times.
Sources
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