Electric bike batteries catching fire - Are you worried?

Battery fires involving electric-assisted bicycles are on the rise and are often in the news. We've reported on fires involving electric bikes here. But how common are they? If you own an electric bike, how likely is it to catch fire? What can be done to prevent this?

How does an electric bike's battery catch fire?

Lithium-ion batteries used in electric assisted bicycles, electric scooters and other light electric vehicles (LeVs) can catch fire due to thermal runaway. In short, a short circuit occurs when there is a fault inside the battery (usually caused by a manufacturing defect, misuse, or external damage), which releases a large amount of heat inside the battery. This heat triggers a chemical reaction, which in turn generates more heat which causes the chemical elements inside to be destroyed, which in turn generates more heat. This chain reaction can spread to other areas, releasing huge amounts of toxic gas and heat in a matter of minutes. The fire burns very hot, and because its chemical reaction does not depend on oxygen in the outside air, it is difficult to extinguish

Fortunately, thermal runaway is uncommon and largely preventable.

 

How common are battery fires in electric bicycles?

It is difficult to know exactly how many fires have been caused by electric-assisted bicycle batteries worldwide. However, a recent report by Electrical Safety First, the UK's leading electrical safety charity, sheds some light on the UK figures. The agency said that according to data from Zurich insurance company, electric bicycles and electric scooters in the UK caused a total of 167 fires in 2021. In 2022, the London Fire Brigade reported that in Greater London alone, there were a total of 87 fires caused by electric bicycles and 29 by electric scooters.

 

It's hard to translate these figures into percentages of electric bikes that caught fire, as we don't know exactly how many electric bikes will be in use in Greater London in 2022 or in the UK in 2021. However, according to Cycling Industry News, 160,000 electric bikes and 175,000 electric scooters will be sold in the UK in 2021. Thanks to the steady increase in sales in previous years, and the fact that e-bikes usually last for several years, we can be confident that there will be hundreds of thousands of e-bikes and e-scooters in the UK in 2021, which matches the 167 fires reported that year.

 

In addition, these sales figures do not include modified parts for electric assisted bicycles, and the fire report data does not distinguish whether electric assisted bicycles have been modified.

 

The good news is that the Swedish Civil emergency Agency MSB conducted a study called "Fires in electric vehicles in 2022", which provides information on the number of electric bicycle fire accidents and electric bicycle sales in Sweden. In 2022, there were 20 fires involving electric bicycles and 38 fires involving electric scooters, the report said. According to the report, a total of 608,000 electric bicycles were sold in Sweden between 2014 and 2022. This still doesn't tell us how many electric bikes there are already in Sweden in 2022, as some may have been recycled/disposed of and some may have been scrapped. Some electric bikes sold before 2014 May still be in use. But to use that number as a rough guide, the 20 e-bike fires that occurred that year equated to 0.003% of the 30,000 e-bikes "on the road" that year, or 1 in 30,000 that caught fire. If only half of all electric bikes are still in use by 2022, that chance rises to 1 in 15,000. By contrast, the same report notes that while the number of electric car fires in Sweden is much lower (about 1 in 30,000), including accidents and arson, an average of about 1 in 1,300 cars a year catches fire.

 

To be clear, the study doesn't say exactly how many electric bikes will be in use in Sweden in 2022, so we can't give an exact figure for the percentage of fires, but I think it's reasonable to conclude that it's about 1 in 10,000 - certainly not 1 in 1,000 or 1 in 100,000.

 

▲Fire coverage of electric vehicles and light electric vehicles reported globally in the first half of 2023. Source: EVFireSafe

 

How dangerous is a battery fire on an electric bike?

While battery fires are relatively rare, several people have been killed by electric bikes and scooters catching fire in their homes. A media analysis by Electrical Safety First documented 36 incidents in the UK in the 12 months between April 2022 and March 2023 in which electric assisted bicycle or electric scooter battery fires resulted in property damage. Of these, 81% occurred at home and half occurred at night. In the first three months of 2023 alone, four people were killed in fires caused by electric assisted bicycles and scooters in the UK. In New York City, fire officials reported six such deaths in 2022 alone and five in the first four months of 2023.

 

To understand the dangers of electric bike fires, we need to expand our view to a global scale. Data on battery fires around the world was collected by EV FireSafe, an Australian government-funded, firefighter-led organisation that studies battery fires in electric vehicles and how to deal with them. Their research is cited by national fire agencies around the world. While they were unable to tally the total number of light electric vehicle fires worldwide, they recorded 138 injuries and 36 deaths from light electric vehicle fires in the first half of 2023.

 

Thirty-six deaths in six months may sound shocking, but it's actually worth noting that the global light electric vehicle fleet is expected to reach 300 million by 2023. In the UK, by comparison, 1,633 people will die in road accidents in 2023, plus an estimated 10,000 premature deaths due to air pollution, but the air pollution deaths are only spread across 41 million vehicles (cars, vans, buses, etc.).

 

Thus, while the frequency of fatal light electric vehicle fires is increasing, on a per-vehicle basis, other modes of transportation are several orders of magnitude more dangerous to life *. This is relevant because a large proportion of electric assisted bicycles are used as a direct replacement for cars.

 

* Side note 1: There is, of course, a risk of accidents associated with cycling or electric bicycles as a means of transportation, but according to a Danish study, this risk is far outweighed by the life-extending benefits of the sport. In addition, I think that a cyclist being hit by a car is an accident risk in terms of traffic, not a risk caused by cycling.

 

Side note 2: According to the International Energy Agency, the replacement of cars and motorcycles with electric bicycles, electric scooters and other light electric vehicles has reduced the demand for oil by 100,000 barrels per day.

 

Which electric bicycles have the highest risk factor?

Electrical Safety First warns against buying electric bikes, modified parts and batteries from third-party sellers on online marketplaces, "which may not meet the correct safety standards," and "DIY modifications to electrical systems (to extend battery life and increase speed limits)." Another risk comes from "universal" chargers, which can sometimes overcharge the battery, exceeding the maximum voltage and causing thermal runaway. The ESF found that nearly 60 substandard electric bike and e-scooter chargers were being sold through third-party online sellers. EV FireSafe also emphasized this point.

▲According to "Electrical Safety First," the biggest risk seems to come from DIY modifications or modified electric bicycles. Source: Electrical Safety First

 

"Many of the modified parts on the line do not contain batteries, which are an essential part of any electric-assisted bike. Choosing the right battery and charger is up to consumers to ensure compatibility and make their own decisions. When a consumer retrofits a regular bike into an electric-assisted bike, they take on the role of the manufacturer from a legal point of view (perhaps unwittingly), and therefore bear full responsibility for safety and the consistency of applicable laws, "- Electrical Safety First.

 

It's unclear how many of the aforementioned light electric vehicle fires were caused by substandard batteries, substandard chargers, or DIY modifications, but it stands to reason that e-assisted bikes built by reputable manufacturers and equipped with the right chargers should have a lower than average risk of failure.

 

To be clear, this is not to say that everyone should avoid using modified parts or entry-level electric bikes (these are the most accessible, sustainable and affordable modes of transportation for many people), but to be cautious about homemade parts and wary of dodgy sellers on eBay/Amazon.

 

It is also worth noting that some bike shops refuse to service low-quality electric assisted bikes. According to EV FireSafe, "This leads to repairs' behind the scenes' with dire consequences."

 

ESF recommends buying only from reputable retailers and using the right charger and compatible batteries. If you can, it is best to charge your electric assisted bike outside in a shed or bike public parking area. If charging indoors, avoid overnight charging, charge away from the outlet and unplug the charger after charging.

 

▲Risk profiles for different battery-powered devices. Source: EVFireSafe

 

Why are electric bikes more likely to catch fire than electric cars?

Talking about the electrical power bicycles and electric scooters, EV FireSafe have begun to use the term "personal mobile devices" (PMD), rather than "light electric vehicles" (LEV), in order to avoid and registered on the road of electric vehicles, electric cars, for example) confusion. This is because electric vehicle batteries are much less likely to catch fire than PMD batteries such as electric-assisted bicycles. In fact, EV FireSafe estimates that the probability of an electric car catching fire is 0.0012%, which they say is much lower than the risk of PMD or internal combustion engine cars. This point echoes the Swedish study mentioned earlier.

▲There are differences between LeVs (such as electric assisted bicycles) and electric vehicles on the road. Source: EVFireSafe

 

According to EV FireSafe, the safety difference between electric-assisted bicycles and electric vehicles is due to a number of factors, "mainly the quality of lithium-ion batteries and battery management systems; In the case of electric vehicles, they are of very high quality and subject to strict regulation, whereas PMDS tend to be of very low quality and poorly regulated."

 

main point

• Batteries in electric assisted bicycles (and other light electric vehicles, such as electric scooters) can catch fire while being charged, which can lead to a particularly serious fire hazard when charged indoors.

 

• Such fires are becoming more common and have resulted in casualties. But such fires are still uncommon compared to the number of electric bikes and other light electric vehicles available. Traffic accidents and air pollution cause hundreds of times as many deaths and injuries as each electric bike, so the risk of fire should not be a factor preventing you from buying an electric bike, especially if you plan to use it as an alternative to car travel.

 

• The most likely to catch fire are electric bikes that have been modified or charged incorrectly, or that are sold by third-party online sellers who do not comply with safety regulations.

 

• If charging an electric bike at home, it is best to place it away from the exit and avoid charging overnight.

 

• The risk of fire is extremely low for a good quality and properly used electric assisted bicycle.