Class L confusion – why a label isn’t a standard when it comes to battery storage

Lithium-ion batteries are almost everywhere these days. They are in power tools on the scaffold, drones across job sites, IT equipment in the office and e-micro mobility devices (including e-bikes and e-scooters). The batteries powering these devices have changed how we work, but, unfortunately, what hasn’t kept pace is how we store them safely.

The lithium-ion battery market has grown faster than the standards governing it, and, where there is demand, inevitably there is a rush of suppliers. Some have the engineering expertise to back up their products. Others don’t, and it is a glaring knowledge gap that is potentially creating a serious safety problem on construction sites across the UK.

You might have seen battery storage cabinets marketed as “fire rated” or “class L approved”. Those claims might sound reassuring, but they are often superficial: the reality requires closer scrutiny.

For decades fire-classification standards have covered categories including class A (solid materials like paper and wood), class B (flammable liquids), class C (energized electrical equipment) and class D (combustible metals). Lithium-ion battery fires don’t fit neatly into any of these. They introduce a distinct set of different risks: thermal runaway, where an internal fault causes a cell’s temperature to spiral upward until its own chemical reactions generate heat faster than it can escape; cell-to-cell propagation, where that heat triggers the same runaway reaction in neighbouring cells turning a single failure into a cascading fire; venting, where a cell’s built-up internal pressure ruptures its casing and releases hot, flammable, and often toxic gases, frequently igniting a fire and spreading it further; and the risk of delayed re-ignition. Unsurprisingly, a cabinet tested against a paper fire will not perform the same way when a lithium-ion cell vents.

A new classification of fires standard this year BS ISO 3941:2026 has introduced the class L (lithium) fire classification, which is a dedicated category for lithium-ion cells and batteries where no metallic lithium is present. The Fire Protection Association has noted specific class L hazards: rapid heat release, explosive gas build-up and projectile risk from expelled cells. Delayed re-ignition from stranded electrical energy is another

The standard states that ISO class L is “particularly useful in the context of [testing] equipment for fire protection and firefighting”. That word choice is telling: it is a recommendation, not a requirement. Nothing compels manufacturers to test their equipment against a lithium-ion fire before bringing it to market. A cabinet or extinguisher can pass every existing fire test and still never have faced one of the hazards it is now most likely to encounter.

On top of this, there is as yet no harmonised European battery storage standard. The British and European standards bodies are working towards alignment, but in the interim, the market is in a grey area. Manufacturers are not obligated to meet a single, verifiable benchmark. That creates room for products to carry credible-sounding labels while being untested against the actual hazards they claim to address.

It means manufacturers, whether deliberately or ignorantly, may apply the “class L” label without conducting genuine lithium-ion fire-safety testing, and that products originally tested against class A criteria can be sold inappropriately as lithium-ion battery-storage solutions.

A new classification of fires standard this year BS ISO 3941:2026 has introduced the class L (lithium) fire classification, which is a dedicated category for lithium-ion cells and batteries where no metallic lithium is present.

What we find when we look at some products on the market is sobering: textile storage bags, metal cabinets rated for standard fires, and enclosures with no ventilation design – all being marketed for lithium-ion use. Under actual lithium-ion fire conditions, many fail catastrophically, despite the ratings attached to them.

Products like this are being sold on the basis of fire ratings that don’t apply to the hazard they actually face. But in a lithium-ion fire, the consequences of a failed cabinet are irreversible – and can put the lives of site personnel at risk.

Independent, real-world testing against lithium-ion fire conditions must be the baseline, with trials and experiments ongoing as the technology changes.

Beyond product selection, several other areas of practice also determine whether your lithium-ion battery storage is genuinely safe. Control of Substances Hazardous to Health Regulations (COSHH) battery-storage requirements are a good starting point, alongside the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR), which apply directly to the fire and explosion risks battery storage presents. Regulations require hazardous materials to be stored away from general work areas, and lithium-ion batteries fall within that scope. Batteries not in use should be stored separately, away from heat sources and other flammable materials.

Ventilation matters too. Lithium-ion battery fires release toxic and flammable gases, so storage should sit in a well ventilated, environmentally controlled space. But room ventilation isn’t a substitute for product design: we find a surprising number of cabinets aren’t built to contain flame while channelling those gases out safely – they either trap dangerous pressure inside or vent it in an uncontrolled manner.

Training is often overlooked, too. Lithium-ion fires behave differently from those most staff have been trained to respond to. People need to understand thermal runaway, why a standard fire extinguisher is the wrong tool, and what delayed re-ignition means in practice.

Fire-risk assessments must now establish whether lithium-ion batteries are present on a premises. That means accounting for their type, quantity and storage arrangements. Fire-safety standards in the UK, including BS ISO 3941:2026, make that a requirement, not a recommendation – a different obligation to the testing question above.

If you are procuring battery-storage equipment, ask for the test data. Not a brochure or a classification label: ask which standard it was tested to, at what energy load, and by whom. If a supplier can’t answer those questions, you have your answer. We all want to work safely. The best way to do that when it comes to lithium battery storage is to stop taking labels on trust – and to start asking for the evidence behind them.

Matt Partridge is head of product development at Armorgard