Safety for Lithium-Ion Batteries: Unfortunately a ‘Burning’ Topic
- The latest on lithium-ion batteries: VdS, Europe’s most important institute for fire protection, has looked at the current state of research and practice concerning these potential hazards and, above all, some protective measures. Most of them easy to ensure and to implement.
The main finding right away: each of us has heard about quite frequent and sometimes uncontrollable fires caused by this young lithium-ion technology. Instead of the good old (and usually harmless) zinc-carbon batteries, which we can still marvel at in low-energy devices like our remote control, the much stronger, very long-lasting lithium-ion batteries are gaining ground in all areas of our lives. They are also regarded by experts as “hyper-sensitive divas who blow up at every little issue” (Institute for Loss Research of German Insurers), significantly increasing the risk of fire.
At the heart of this battery system are electrochemical cells, typically made of an easily inflammable electrolyte. One core problem is the (so far) unstoppable age-related destruction of the diodes’ separator. Because the battery cells are individual, they age at different rates. While ‘young’ cells in the same battery can still have capacity and say ‘give me more’, older cells can already be overcharged, causing them to overheat. The same occurs in the other direction with a dangerous deep discharge (more on this below).
So unfortunately, lithium batteries can ignite due to a number of reasons that were not relevant for zinc-carbon batteries:
- Incorrect handling
- Mechanical damage
- Thermal stress (there are many examples of cars or busses standing in the sun and catching fire, or even exploding)
- Internal or external short circuits
- Deep discharge –unfortunately this technology can also ignite from being empty, possibly leading to spontaneous combustion. But basically, the higher the charging level, the higher the danger.
- Quick charging
Wrong charging equipment – at least one easy thing to prevent
In addition, when a lithium-ion cell is burning, hydrogen can be emitted that can mix with the ambient air and form an explosive mixture. An extinguished battery can also reignite at any time, even days after a fire.
An example of the explosive power that can be released during a fire involving lithium-ion cells can be seen in a recording of a warehouse fire that started off quite small, but quickly became very serious once the cells caught fire. See the link at the end of this article. There was no warning for the firemen – the warehouse manager had stored huge amounts of zinc-carbon batteries for years and understandably did not realize that the similar products with new technology had suddenly become a highly inflammable, even explosive and dangerous item.
Now some good news: quoting the German Insurers Association’s statement after conducting practical tests together with VdS: “When handled properly, lithium batteries do not pose any unusual fire risk; the technology is suitable for everyday use. This means that manufacturers, distributors and consumers have considerable responsibility when dealing with these powerful devices.”
“When Handled Properly” – What Exactly Does That Mean?
The German insurers have bundled their findings and safety advice into a publication that can be downloaded free-of-charge – see the link below – recommending some general safety rules:
- Incoming goods inspection shall ensure that only undamaged cells and batteries are stored, for which UN 38.3 is available as evidence of checking. Special consideration applies to prototypes and returns.
- In any areas not protected by an automatic extinguishing system, a structural or spatial separation of a minimum of 2.5 meters from other combustible materials shall be maintained.
- Do not expose to high temperatures or heat sources (e.g. direct sunlight); 60 °C is specified by well-known manufacturers as an upper limit to protect against capacity loss and increased fire risk. At the other end of the scale, also avoid exposing them to frost. The longer low temperatures affect the cells, the greater the risk of capacity loss and dangerous cell damage, so do not store batteries in an unheated part of a building in winter.
- Adhere to the specifications of the respective manufacturer and technical product data sheets.
- Prevent external short circuits (protection against short circuit of the battery terminals, for example by fitting caps).
- Prevent internal short circuits (protection against mechanical damage).
- Immediately remove any damaged or defective lithium battery from the storage and production area and store this temporarily at a safe distance or in a separate area with fire protection until its disposal.
Always check that the cells are undamaged – which specifically means: a scratch is fine, no problem. If the battery fell down, check whether it has been dented, deformed or perforated. If all three apply, remove it instantly! If it is swollen, treat it like a bomb – it now is one! The best way to transport such a damaged cell is in a fireproof box, but if this is not available a metal wastebasket covering the cell in sand (not water, for chemical reasons) is a ‘quick and dirty’ and comparatively safe option.
Rapid Temperature Increase During Charging is Bad for the Lithium Cells
Also very bad for lithium cells is a rapid temperature increase during charging or a suddenly empty battery. Charging is seen as most critical and should preferably happen only under surveillance and on a fireproof base – please remember this also for your mobile phones and other devices at home. It should also be ensured that batteries have not previously been deeply discharged (such as by limiting the storage time before re-charging them to six months).
The VdS have published a battery classification leaflet entitled ‘Sprinkler Protection of Lithium Batteries’. This can also be downloaded without charge - the link is shown below. This aims to make the results of fire tests more transferable. Since weight and size can vary greatly due to the different cell formats (pouch cells, for example) a classification by energy content per storage unit (pallet) is more useful, classified according to power (Ah). As the voltages can also vary greatly, the power has been converted to kWh.
What To Do in Case of Fire – Very Quickly:
A classic saying applicable to many human activities is: “Anything that can go wrong will go wrong”. So if a battery catches fire, what is to be done? Fortunately, the only extinguishant needed for a developing lithium battery fire is simple water. If efficient fighting of an early-stage fire succeeds within the first few minutes – with rapid and targeted water application –there is a good chance of getting control of the fire. Unfortunately, a fire involving lithium batteries usually gets fully out of control within around eight minutes, which is much less time than is usually needed to detect the fire, sound the alarm, then extinguish it.
Sprinklers Do Work
A caveat to what is written here is that battery power is increasing by approximately 10 % every year, so all current safety plans and some aspects of this article might be totally obsolete in the near future. Nevertheless, intensive VdS testing has proven in practice that the good old water sprinkler extinguishing systems – best of all VdS-approved – are effective protection if they are designed so that water will reach the source of fire quickly. Unfortunately, standardized solutions for this relatively new type of battery do not yet exist – a case-by-case evaluation is necessary at the moment. Check the VdS 3856 guidelines for assistance.
Some of the main findings are summarized for you here. Strong cooling is essential – water is favored as the extinguishing agent for this. It is also necessary to cool batteries that are not yet in the fire because of the thermal runaway danger (stored energy can be released in an uncontrolled manner). So far, only rapid cooling with large quantities of water has proven effective.
As for storage, check that all devices are in drenchable packaging, and that the stored energy per packaging unit (e.g., pallet) should not exceed 50 kWh. The rack design should be according to VdS CEA Planning Guidelines 4001, K.7.1 and sprinkler protection provided on every rack level. Of course, only batteries with proof of testing according to UN 38.3 should be stored, using only batteries from reputable manufacturers with appropriate quality and safety standards.
We hope this summary was helpful to our joint cause of protecting human life, the environment and expensive goods from destructive fire and smoke – best regards to all those working for our safety!
Author: Dr. Florian Scharr, Coordinator for Customer Relations at VdS