On this cold November morning, the grayish sky seems to hang over the immense 240 hectare site of the National Center for Prevention and Protection (CNPP) located in Saint-Marcel, in Eure. The private organization, specialist in the prevention and control of risks, from fire to cybersecurity, has occupied this former BP refinery since 1988. Of the 440 CNPP employees, around 350 work here, in the testing laboratories and training buildings located not far from a cracking tower and giant tanks.
To witness a battery fire and its extinction, an appointment was made in the large test hall where a movable ceiling rises three meters high. This is dotted with sprinkler heads, sort of water-filled bubbles that burst and serve as an extinguishing system in the event of a fire. Under the ceiling, in the center of the hall, a pallet supports 40 electric bicycle lithium-ion batteries made of cylindrical NMC type cells, for nickel-manganese-cobalt.
A fatal accident in South Korea left its mark
To cause thermal runaway, a heating plate was installed on one of these batteries. Around it, other pallets were positioned to study the risk of the flames spreading. Thermal sensors and cameras were also installed to monitor the evolution of the fire from the outside, once the hall was evacuated. “The firing should last about a quarter of an hour,” warns Damien Roubineau, CNPP consultant for new energies.
The test is the second in a series of two tests financed by France Assureurs, the professional insurance organization in France, after a first carried out the previous week. The marketing of the first lithium-ion batteries by the Japanese electronics company Sony dates back to 1991, but concern about the fire risk associated with this technology is growing due to its increasing diffusion with the ecological transition. The fire which cost the lives of 22 workers in a lithium battery factory in South Korea last June left its mark. That of a Snam warehouse last February in Aveyron is also remembered.
“These batteries will be even more present in our lives tomorrow”
“Fire remains the leading cause of losses in businesses. We have been monitoring this risk for decades but it continues to evolve, with the new development of lithium-ion batteries. These batteries are already very present in our lives today and they will be even more so tomorrow. We need to know how fires linked to these batteries develop and how to contain them. justifies Florence Lustman, the president of France Assureurs. Behind her, several video feeds of the test appear on the screen, one of which comes from a thermal camera. A synoptic table makes it possible to follow the evolution of the temperature and thermal radiation at different locations on the scene. In this same hall, the CNPP regularly carries out so-called “abusive” battery tests, in particular for European manufacturers of this technology.
For France Assureurs, the objective of this test campaign is to collect data on the propagation of this type of fire. It must also make it possible to test the effectiveness of the sprinkler system to then improve the protection of property and people in contact with these batteries and reduce the consequences of a disaster. In fact, for prevention experts, the difficulty with batteries lies in the diversity of their shapes and compositions. This makes the development of a “typical home” complex.
Cover as many real-life situations as possible
“Sometimes batteries from the same series don’t even react the same way,” assures Damien Roubineau. The first two tests financed by France Assureurs will therefore be insufficient to provide a complete response to the issue of battery fires. Today's test only concerns a fire due to an increase in cell temperature. But short circuits can also occur in the event of excessive mechanical pressure exerted on a battery or following a deep discharge, for example. “What we are less good at doing is putting out these fires. The cells are generally placed in boxes to protect them, which complicates our attempts to get water into the home. completes Damien Roubineau.
The test configuration aims to cover as many real-life situations as possible, through a scenario representative of temporary storage of batteries at the end of the line in a factory or in a battery marketing company. “We also find these bicycle batteries almost everywhere and we are talking about fires with a very high risk of mortality, because they can take place at night, in a hallway in a private home,” says Damien Roubineau.
Tests that take a long time to prepare and are expensive
Ten minutes after activating the hotplate, black smoke was released from the central vane in the test hall. Then flames appear, accompanied by small explosions and projections of incandescent materials. “It’s a fire that ultimately doesn’t heat much,” observes Damien Roubineau, pointing out the thermal sensor data stuck at 2.5 kW/m2 on the synoptic table. The watering trigger temperature was exceeded at a sprinkler head, without effect. You will ultimately have to wait several minutes after the flames appear to finally see the water drain from the ceiling and gradually stop the fire.
“We are satisfied with this test, the sprinkler contained the fire,” considers Damien Roubineau, while recognizing a slight delay in triggering the device. “It’s only a question of settings and choice of technology,” he adds. “The triggering of the sprinkler was not sensitive enough”, believes Christophe Delcamp, director of damage and liability insurance at France Assureurs, at the end of the demonstration. The real conclusions, however, will come from a working group led by insurers who will analyze the results in more detail. In the future, France Assureurs could order new tests from the CNPP to refine its recommendations. But two obstacles prevent the employers' organization from moving more quickly: the preparation time for a trial of this type is around a year and the cost of the current campaign is already 458,000 euros.
