How dangerous are burning electric cars?
Fire experiments in test tunnel

Date:
September 1, 2020
Source:
Swiss Federal Laboratories for Materials Science and Technology
(EMPA)
Summary:
What happens if an electric car burns in a road tunnel or an
underground car park? In the Hagerbach test tunnel in Switzerland,
researchers and tunnel safety experts set fire to battery cells of
electric cars, analyzed the distribution of soot and smoke gases
and the chemical residues in the extinguishing water.



FULL STORY ========================================================================== There' s a loud bang, and then it starts: A battery module of an
electric car is on fire in the Hagerbach test tunnel. A video of the
test impressively shows the energy stored in such batteries: Meter-long
flames hiss through the room and produce enormous amounts of thick,
black soot. The visibility in the previously brightly lit tunnel section quickly approaches zero. After a few minutes, the battery module is
completely burnt out. Ash and soot have spread throughout the room.


========================================================================== Crucial information for multi-storey and underground car parks The
trial, which was funded by the Swiss Federal Roads Office (FEDRO) and
in which several Empa researchers participated, took place in December
2019. The results have just been published. "In our experiment we were considering in particular private and public operators of small and large underground or multi-story car parks," says project leader Lars Derek
Mellert of Amstein + Walthert Progress AG. "All these existing underground structures are being used to an increasing extent by electric cars. And
the operators ask themselves: What to do if such a car catches fire? What
are the health risks for my employees? What effects does such a fire have
on the operation of my plant?" But until now there has been hardly any meaningful technical literature, let alone practical experience for such
a case.

With the support of battery researcher Marcel Held and corrosion
specialist Martin Tuchschmid from Empa, Mellert developed three test
scenarios. Experts from the Hagerbach AG test tunnel and the French Centre d'e'tudes des tunnels (CETU) in Bron were also involved. "We installed
test surfaces in the fire tunnel on which the soot settled," explains
Martin Tuchschmid, corrosion and fire damage specialist at Empa. "After
the test, the surfaces were chemically analyzed and also stored in
special rooms for several months to detect possible corrosion damage."
Scenario 1: Fire in an enclosed space The first scenario involves a fire
in a closed car park without mechanical ventilation. A parking space
of 28 x 28 meters area and 2.5 meters floor height was assumed. Such a
floor would have an air volume of 2000 cubic meters. The fire of a small
car with a fully charged battery of 32 kWh is assumed. For reasons of
test economy everything was scaled down to 1/8. Thus, a fully charged
battery module with 4 kWh capacity was set on fire in a room with 250
cubic meters of air volume. The tests investigated how the soot settles
on tunnel walls, surfaces and on protective suits worn by firefighters
on site, how toxic the residues are and by what means the fire site can
be cleaned after the event.



========================================================================== Scenario 2: Fire in a room with sprinkler system Scenario 2 deals with
chemical residues in the extinguishing water. The test set-up was the same
as in scenario 1. But this time, the smoke from the battery was channeled
with the aid of a metal plate beneath a water shower that resembled a
sprinkler system. The sooty water that rained down was collected in a
basin. The battery was not extinguished, but burned out completely.

Scenario 3: Fire in a tunnel with ventilation In this scenario, the focus
of the study lay on the effect of such a fire on a ventilation system. How
far is the soot distributed in the exhaust ducts? Do substances that
would cause corrosion settle there? In the experiment, a 4 kWh battery
module was again set on fire, but this time a fan blew the smoke at a
constant speed into a 160-meter-long ventilation tunnel. At a distance
of 50, 100 and 150 meters from the site of the fire, the researchers had installed metal sheets in the tunnel where the soot would settle. The
chemical composition of the soot and possible corrosion effects were
analyzed in the Empa laboratories.

The results of the test were published in a final report in August 2020.

Project leader Mellert reassures: In terms of heat development a burning electric car is not more hazardous than a burning car with a conventional drive. "The pollutants emitted by a burning vehicle have always been
dangerous and possibly fatal," says the final report. Regardless of the
type of drive or energy storage system, the primary objective has to
be to get everyone out of the danger zone as quickly as possible. The
highly corrosive, toxic hydrofluoric acid has often been discussed as
a particular danger in burning batteries. In the three tests in the
Hagerbach tunnel, however, the concentrations remained below critical
levels.



========================================================================== Conclusion: A tunnel ventilation system that is state-of-the-art can
cope not only with burning gasoline/diesel cars, but also with electric
cars. Increased corrosion damage to the ventilation system or the tunnel equipment is also unlikely based on the results now available.

Even the fire brigades do not have to learn anything new on the basis
of the tests. Firefighters know that the battery of an electric car is impossible to extinguish and that it can only be cooled with large amounts
of water. So the fire can possibly be limited to a few battery cells,
and part of the battery will not burn out. Of course, such a partially
burnt wreck must be stored in a water basin or a special container so
that it cannot reignite. But this is already known to the specialists
and is being practiced.

The extinguishing water is poisonous A problem, however, is the
extinguishing and cooling water that is produced when fighting such
a fire and storing a burnt-out battery in a water basin. The analyses
showed that the chemical contamination of the extinguishing water exceeds
the Swiss threshold values for industrial wastewater by a factor of 70;
the cooling water is even up to 100-times above threshold values. It is important that this highly contaminated water does not enter the sewage
system without proper treatment.

Professional decontamination mandatory After the trials, the tunnel
was decontaminated by a professional fire clean-up team. Samples
taken subsequently confirmed that the methods and time required were
sufficient for the clean-up after an electric car fire. But Mellert warns especially private owners of underground garages: "Do not try to clean
up the soot and dirt yourself. The soot contains large amounts of cobalt
oxide, nickel oxide and manganese oxide. These heavy metals cause severe allergic reactions on unprotected skin." So clean-up after an electric
car fire is definitely a job for professionals in protective suits.

https://www.youtube.com/watch?v=2O07SIaxB08&feature=emb_logo

========================================================================== Story Source: Materials provided by Swiss_Federal_Laboratories_for_Materials_Science_and
Technology_(EMPA). Original written by Rainer Klose. Note: Content may
be edited for style and length.


==========================================================================


Link to news story: https://www.sciencedaily.com/releases/2020/09/200901112208.htm

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