Overview

Most EUCs use lithium-ion batteries, which, unfortunately, can ignite into intense fires if misused. Electroheads provides an excellent overview in this video:

Thankfully these fires are rare. An organized effort to catalog fires at the Electric Unicycle Forum has only found 58 as of November 2022. Estimates put the number of EUCs at more than 100,000, so the resulting odds of a fire are less than 1 in a thousand wheels. Many of these fires have been concentrated in a handful of Begode models, so for other models the odds are probably less than 1 in 10 thousand. And this statistic includes the obvious cases of misuse like a wheel being dropped in a lake.

Still, there’s plenty you can do to reduce the risk.

In the absence of important safety certifications like UL 2272, it’s important to buy EUCs from reputable manufacturers and distributors who will do basic safety checks.

You can further ensure your safety by following a few simple charging rules, keeping a smoke detector near where the wheel is stored and charged, monitoring your wheel’s voltage levels, and inspecting your batteries yearly. A fireproof container or fire extinguisher tested specifically for lithium-ion battery fires can also help.

A couple of wheels are sold with lithium iron phosphate (LiFePO4) batteries. These batteries will not have the same thermal runaway as regular lithium-ion batteries, so the fire risk is removed.

How to charge lithium-ion battery packs

There are just a few things to do regarding charging.

First, only use chargers compatible with your wheel. Using a charger with a higher voltage (“overcharging”) may start a fire.

Second, don’t allow the batteries to be depleted. I assume that the “0%” battery level shown by the apps is a safe level, but if the battery is neglected for an extended amount of time and goes below that level (“overdischarge”), the battery may be badly damaged. In this case, don’t attempt to charge it. You should either take the batteries to an experienced battery repair person to see how bad the damage is, or just recycle them.

Third, balance your batteries regularly. This implies fully charging the battery and leaving it on the charger for a few more hours. When the pack is nearly fully charged, it will automatically start balancing the cells. Onewheel expert Mario Contino explains in detail here (this generally applies to both Onewheels and EUCs):

When to worry

In general, it’s a good idea to check that the battery charges as expected. It’s also a good idea to inspect the battery for damage after a hard impact, or once a year. Here are some warning signs to look out for:

  • battery doesn’t charge
  • battery voltage drops much faster than usual
  • battery charges, but not fully
  • battery has been exposed to water
  • battery is rusty or deformed

If the battery doesn’t charge, or the voltage/battery level drops much faster than usual, this indicates that the battery has a short. If the battery charges, but not fully, this could indicate that cells are damaged or that the cells are imbalanced. Water often causes a short if it gets into the battery. And physical damage to the battery can cause a short. Any of these are a cause to consider the battery a fire hazard, and the battery should probably be recycled.

Pre-production wheels and EUC models with a history of fires call for extra caution, for obvious reasons. The Electric Unicycle Forum is one good source to check for fire history.

Lithium-ion batteries should not be thrown away. In the US, they can be recycled at Home Depot, Best Buy, Staples, and other stores. See the EPA’s guide for more info.

How to stop a fire

Because lithium-ion battery fires are difficult to extinguish, it’s important to use products that have been rigorously tested for lithium-ion battery fires. (Mario Contino shows how one poorly tested product fails in a video here.)

Submerging a wheel in water is a cheap and low-tech way of stopping a fire, if you can find a safe way to do it. I would only consider a fireproof sack or case for smaller battery packs, because containers made for larger battery fires are expensive.

In my opinion, a fire extinguisher (one tested specifically on lithium-ion battery fires) is the most practical way to stop most fires. Though even this option may not be safe in many cases.

Battery fires often reignite after being extinguished with traditional extinguishers or water.

Lithium-ion battery fires release toxic gases, including hydrogen fluoride and carbon monoxide.

Submerge in water

Unlike many other fires, spraying water will not stop a lithium-ion battery fire. Instead, you need to completely submerge the batteries in water. When submerged, the water cools the batteries enough to end the thermal runaway. (When removed from the water, the batteries can ignite again.)

Fireproof sacks/cases

There are lots of fireproof lithium-ion bags and containers, though most are meant only for storing battery packs rather than an entire wheel (and usually smaller battery packs like you might see for a drone). FireSak is one made for EUC riders. I’m not fully convinced by the FireSak tests, but it may control some fires, especially for smaller battery packs.1

CellBlock FCS, Empteezy, and Nauta all make more robust cases that can contain larger battery fires. The downside is that they’re expensive (thousands of dollars).

Fire extinguishers

Traditional fire extinguishers aren’t effective against lithium-ion battery fires, but there are alternatives.

F-500 EA and AVD are two of the more common extinguisher types that work specifically against lithium-ion battery fires. They’re sold under different brand names in different countries. Of these, F-500 EA seems to require the least volume of extinguisher per watt hour, so I recommend it for larger battery packs. In the US, F-500 EA extinguishers can be bought directly from Hazard Control Technologies.

Class D fire extinguishers are not effective against PEV fires. These extinguishers are for metallic lithium, not the ionic lithium in PEV batteries.

CellBlockEX is a dry granulate extinguisher that can stop thermal runaway. Rather than using a hand-held extinguisher, you set a bag of this on your unicycle so that it will be released if a fire starts. In an email, they recommended “2-3 cubic inches of CellBlockEX per 1 Wh,” which translates to 2 or 3 of their 55 liter bags for a larger EUC.

As of January 2023, the Dutch standard NTA 8133 is the only relevant fire extinguisher certification I know of. This standard requires testing a 9 liter extinguisher to show it can put out a 600Wh battery fire. Unfortunately this is of limited use since EUC batteries are usually larger. The Dutch testing company Kiwa has some sobering advice for the use of these fire extinguishers (translated from Dutch here and here):

Can anyone who has an NTA 8133 tested extinguisher now extinguish a Lithium fire?

No, extinguishing a lithium fire is a job for professionals. In addition to the (health) hazards that such a fire entails, the extinguishing technique is also important in a lithium battery fire. In the event of such a fire, always call the emergency number and leave the room where the fire is located.

The importance of protective equipment

Many harmful substances are released during the combustion process of a lithium cell. In addition to the combustion of the plastic packaging, hydrogen fluoride is also released during such a fire. Persons run a serious health risk when they come into contact with the toxic fumes that are released. Minor exposure to these vapors often requires medical treatment.

The use of protective equipment and ventilation is therefore essential. This includes the use of respiratory protection or a full face mask. In the NTA 8133:2021, the ventilation and the use of personal protective equipment (PPE), when projecting a lithium fire extinguisher, is therefore included as advice.

(Lack of) safety certifications

UL 2272 is the relevant battery safety standard for e-mobility devices like hoverboards and e-scooters, and, presumably, EUCs. It was created in response to hoverboard fires, and requires a variety of common-sense tests of the vehicle and battery system.2

IEC 60335-2-114 is another standard for “Personal-e-Transporters” focused on electrical safety, and it explicitly includes electric unicycles. IEC is an international organization and its standards are voluntary, though many have been adopted by the European Union and UL. The standard requires IPX4 water resistance and the ability to withstand water immersion up to the pedals/floorboard, among other things. IEC 60335-2-114 is put together by the IEC’s Technical Committee 125.

As of November 2022, I’m not aware of any EUCs with UL 2272 certification. I’m also not aware of any model that claims to meet the IEC 60335-2-114 standard. In the absence of these certifications, it’s important to buy EUCs from reputable manufacturers and distributors who will do basic safety checks. Among other things, distributors handle recalls of defective parts, and some ship wheels with safer battery packs than you’d get directly from the manufacturer.

For the batteries themselves, there’s both UL 2271 and CE certification. Of the two, UL 2271 is more comprehensive, and I don’t know if any EUC batteries currently have it. On the other hand, most if not all EUC batteries have CE certification because it’s required to sell the batteries in Europe. CE certification requires compliance with EN 62133-2, which includes tests for crushing, mechanical shock, overcharging, short circuits, and more.

In 2019, the European Commission funded a study of e-scooters, e-bikes, hoverboards, and electric unicycles, to test their compliance with European standards, including EN 62133-2 and IEC 60335-2-114. 3 unicycles were tested, and all were found to be compliant with the standards.3 So there’s some evidence, albeit very limited, that many EUCs meet the relevant safety standards.

  1. Here’s a video of a FireSak test from Ginger On Wheels, who sells the FireSak. Meanwhile, this video from Go George Go captures a real Begode Monster Pro fire in a FireSak. (It does not go well.) The FireSak testing does not seem comparable to a bad EUC fire. ↩

  2. For more info about UL 2272, see UL 2272 and the Safety of Personal e-Mobility Devices. ↩

  3. CASP 2019 - Personal Transporters. I’m annoyed because the graphs in the report mistakenly label the EUCs as non-compliant. The text and numbers in the report, and the results in the detailed annex document, all show that the EUCs were compliant. In contrast to the EUCs, hoverboards were non-compliant due to poor water resistance. Many e-scooters and e-bikes were also non-compliant, but mostly for mechanical issues that don’t apply to EUCs. Unfortunately they don’t say which models were tested. ↩