The risks of the electric car.

The  70-liter fuel tank of a gas-powered car stores a considerable amount of  energy, commonly 700 KWh, and gasoline is a volatile, obviously  flammable product.
The risk we think of is obviously the accident followed by a fire with victims stuck inside. 

 What about it?
The  following data are extracted from the statistics of fire and rescue  services for the year 2012 (SDIS 13 BD), from the Ministry of the  Interior.
They report the number of victims rescued:
In a house fire: 14,176, including 280 dead and 1,054 wounded.
In a vehicle fire: 2,415, including 29 dead and 83 wounded.
The risk of perishing in a fire, or being injured, is 12 times higher at home than in his car.
Tens of thousands of cars burn every year, spontaneously or with a little help. In the vast majority of cases there is no one inside.
The  risk can therefore be considered very low, compared to the 35 million  vehicles in the park, and the 420 billion kms traveled each year.
Spontaneous or criminal car fires cause very few victims, possibly collateral.
For car fires that have resulted in casualties, these are essentially the result of road accidents.
These fires are often the result of an electrical short circuit, despite the low value of the battery voltage (14 V).

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The arrival of electric cars justifies a new risk analysis.
The absence of a fuel tank could suggest that there is no risk of fire.
It is to forget a little quickly the dangers of electricity, and the battery itself.
In an EV, not only 14 Volt are present, but 400 V, and soon 800 V with high capacity batteries.
As for the current "available", it can reach overload several hundred amperes, and much more in short circuit.
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This  exotic object is a Lithium-ion battery therefore represents a  significant risk of electrification of people in case of malfunction of  the battery itself, the car wiring, the motor insulation, the integrity  of the batteries. insulation sleeves and / or the tank containing the battery.
Another  risk of electrification is related to the intervention of the personnel  of breakdown, towing, or intervention on accident if these personnel  did not receive the essential training for this type of vehicles.
A  more general risk of electrification is related to the presence of  moisture, even splashing water, or even falling into a flooded ditch.
Let's not forget that water is electrically conductive, especially since it is dirty and   polluted. 

 In addition to this serious risk if all precautions are not taken, there is the risk associated with the battery itself.
During an accident, there may be a short circuit that will be the triggering event of a fire.
During the fire, the combustion of cabin materials can release toxic gases causing intoxication of people.
This fire can reach the area of ​​the battery, and cause its destruction (explosion) with emission of toxic products.
On the other hand, the deformations of the passenger compartment can be at the origin of the electrocution of people.
Apart  from any accident, a fire can be triggered by the battery itself, under  the effect of an overload due to an internal short circuit. This  fire then leads to the release of toxic substances, or even an  explosion, with the damage that we imagine for the entourage.
Without  even invoking an external disaster, the battery may be in a state of  overheating or internal short circuit due to inappropriate use such as  bad charging conditions, or excessive charging current, degradation due  to aging, or a failure of the BMS (Battery Management System).
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These  risks must therefore be taken into account in order to establish safety  rules for users, rescue and response personnel in case of fire, and  towing or mechanical interventions.
You  do not approach an electric car without taking special precautions that  must be known by those who are likely to deal with it.
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Lithium-ion car batteries consist of elementary cell assemblies with a nominal voltage of 3.7 V at 20 ° C.
The  optimal current-voltage compromise to provide a power of about 60 to 80  KW to the electric motor of the vehicle led the profession to choose a  voltage of 400 V for the battery.
To obtain this value it is necessary to place in series about 108 elementary cells of 3.7 V.
But in this case, if one of the cells is faulty, the entire battery becomes inoperative.
To avoid this disadvantage, we use not a single series of 108 cells, but a dozen that are placed in parallel.
In  this way, if one of the batteries is HS, it can be disconnected and the  battery remains operational, with 10% loss of capacity.
We then have in this example 1080 elementary cells!
But we can have many more.
For example, Tesla used (may still be using) a small element Panasonic (NCR 18650 B) 3.3 Ah, 12 Wh.
It was therefore necessary to use 7,083 to reach a total capacity of 85 KWh!
In general we try to stick to about 2 or 3,000 cells.
Each elementary cell has a predicted failure rate under the conditions of use corresponding to the automotive specifications.
The predicted rate of all the cells is multiplied by the number of cells.
The more there are, the more the failure rate increases.