Electric cars on fire and bathing

Probably no discussion on the topic of electric cars and their future is complete without mentioning the argument that electric cars (or rather their batteries), if they are burning, they burn like candles.


Is this true and how safe are electric cars? Let's try to figure it out.
And for starters, a couple of stories with headlines and disclosures explained:

Lyrical digression: The article is inspired by the theme of Modern Automotive. Electric vehicles - the disruption of the covers of a respected kababok and is its addition / extension.

It can also be considered a detailed response to a comment from Igor_O to another article.
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Table of contents

• Spectacular conflagration
• What does ADAC say?
• What do the firemen say?
• And what, engines do not burn
• What are the conclusions from all this?

"Spectacular conflagration", "auto transporter with electric cars completely burned down"



German burned out in Tesla Fire intensified because of the battery?


Burned out in an electric car: the parents of a dead teenager sued Tesla


Yeah, the pictures and the headlines are terrifying (what else can you expect from BILD), but let's understand how things really are. And first we ask:

What does ADAC say?

And ADAC says that (further quote, but not verbatim) :

The risk of fire is relatively low, since current electric vehicles in the event of an accident are just as safe as normal ones, and the high-voltage system is usually turned off after an accident when the airbag is triggered.

Critical can be the case if the battery protection is damaged as a result of an accident. In this case, the elements in the battery can "leak", which can cause "Thermal Runaway": then the battery is very difficult to put out.

ADAC conducted a comparison of VW e-up! with normal VW up! which showed that in crash tests both cars gain 5 stars.
I note only that the battery in the VW e-up! it was reinforced with a frame, which naturally gives the necessary rigidity, but also adds about 250 kg of weight. What naturally does not add to the VW e-up!

At the end of the ADAC notes that

During the side and pole impact no dangerous deformations were recorded on the battery case.

Side impact with rammers and piles are of particular importance for modern electric vehicles. Since the space for the deformation of the car from the side is less than the back or front, in this case the side impact is the weak point of the electric vehicle ...

Here it is necessary to take into account that in crash tests a side impact is applied by a ram at a speed of 50 km / h, a pile strike is 34 km / h. The scale and risk of deformation at higher speeds do not provide any information.

What do the firemen say?

And the firemen say that

A burning battery can only be cooled, cooled and cooled. For hours, maybe days ...

For hours, maybe days ...

For Tesla Model S, this requires up to 11,000 liters of water, (according to the manufacturer
(I did not find a note from me - I did not find references to this data, I have to believe a word for the correspondent / fireman).
Usually a fire truck carries between 1,500 and 2,000 liters of water. This is enough for the fire brigade to put out the car with the internal combustion engine or a fire in the house.

In the event of an accident, the approach to electric vehicles is not fundamentally different from the approach to the engine, it is necessary:

• Put the system in a safe state.
• Protect the car from rolling off. (whatever it is, this is the difficulty of translation, there is a smiley here)
• Put the car system in a safe condition.
• Turn off the high voltage system.
• Disable 12V system.
• Tools - water, foam, powder.

But there are additions regarding EV:

• Cannot cut HV battery
• Avoid cutting high voltage cables / components
• Foam is preferred for tires and plastic parts.
• Water is the preferred means of extinguishing HV-batteries / systems. much water
• It is advisable to continue to cool the battery with water after extinguishing the fire.
• Depending on how much water gets on the battery and how it is damaged, self-production of detonating gas (oxyhydrogen) is possible.

And what, dvs cars do not burn?

For the sake of justice, it should be noted that usually the engine-internal combustion engine can ignite because of the 12V battery, mainly when:

• short circuit
• at overheating.

But even if this happens, then the usual foam is enough to quickly extinguish the fire. (unless of course time to recall). In the case of a lithium battery, one fire engine may not be enough.

What conclusions can be drawn from all this?

• Do not drive under 140 where the limit is 40.
• Do not fall under the side ram, it's better in the forehead.
• Do not overheat the HV battery.
• The main reason for the ignition of the lithium battery in an accident can be considered as its deformation (hi Samsung Note).
• If caught fire, it burns quickly and brightly and burns to the end.
• Water is poured in the first place in order to cool the battery (hello Fukushima).
• And most importantly: electromobiles are no less safe than ordinary ICEs, and due to the design, they are sometimes safer than their counterparts. (Who would doubt that)

PS:

In addition to all the new things that a growing number of electric cars introduce, questions are added from the point of view of rescuers and firefighters:

• how should firefighters be trained?
• what kind of fire engines are needed to extinguish electric vehicles in case of anything: it should be one or two specials. firefighters with equipment (large tank, etc.) or for each special. means to put?

* But you can create such machines:


^{Electric fire truck for tunnels. Croatia @Ziegler}

Thanks to kababok for encouraging me to write an article and suggested a headline.

Update:

Returning to the question: do lithium batteries burn and how ?, let me quote

So, after a short circuit occurs, the battery starts to heat up. When the temperature reaches 70-90 ° C, the ion-conducting protective layer on the anode begins to decompose. And then lithium, built into the anode, reacts with electrolyte, releasing volatile hydrocarbons: ethane, methane, ethylene, etc. But, despite the presence of such an explosive mixture, ignition does not occur, since there is no oxygen in the system yet.

Since the reaction with the electrolyte is exothermic, the temperature and pressure inside the battery continue to rise. When the temperature reaches 180–200 ° C, the cathode material, usually a transition metal oxide with lithium embedded in the crystal, reacts to disproportionation and releases oxygen. This is where the spontaneous combustion takes place and an even sharper temperature jump. In parallel, there is a thermal decomposition of the electrolyte (200-300 ° C), which also produces heat.

and provide a link to the article How do LadyN's lithium-ion batteries explode (really great article)