We are now waking up to the significant risk batteries pose on building sites says Matthew Partridge
Early in 2025, a lithium-ion battery caught fire overnight on a major UK contractor’s site. Nobody saw it start: the crew found out the next morning, when they opened up the site to the sound of the alarm
By which point, a suppression-equipped charging unit had already contained the fire. The contractor later valued that near miss at a minimum of £318,000 in potential property damage and lost time. It was reported in the trade press: a real fire, on a live site, at a contractor doing most things right.
What should worry the rest of us is how commonplace the cause is. The fire started from a battery sitting on charge, just like the ones sitting in vans, cabins and tool stores all over the country. Today, cordless tools, survey kit, lighting and comms all use lithium-ion battery power. But most safety systems have yet to catch up. The kit is everywhere; the proper habits around its use are not.
Construction also has a problem that other sectors do not. On a busy site, there might be 40 trades, most subcontracted, many bringing their own tools and chargers through the gate each morning.
So, when a battery starts smoking in a cabin at seven in the evening, who brought in that piece of equipment? Who inspected it and who let it charge overnight? On most sites, the honest answer is that nobody properly owns those decisions. Unfortunately, outcomes like this are a failure of leadership and everyday working culture.
How a healthy-looking battery turns dangerous
Batteries fail for a handful of reasons: physical damage is the obvious one, while electrical faults are another. The main cause people underestimate is thermal failure, because it gives so little away.
“In short, a battery can look fine right up to the moment it isn’t.”
Heat wears down cells slowly and invisibly, with most manufacturers putting the safe charging window at 15-30°C. When a battery pushes past that range, the cells degrade faster and it can tip over into thermal runaway, where the cell produces heat faster than it can shed it. Once that process starts, stopping it is close to impossible. Often, there is no warning; there is no smoke or smell; there may be no visible swelling either. In short, a battery can look fine right up to the moment it isn’t.
Why a building site raises the stakes
A lithium-ion fire breaking out is bad news anywhere. If it breaks out on a construction site, it finds plenty of material to work with. These fires burn beyond 1,000°C and emit toxic gas, and they start where the batteries live – next to timber, fuel, packaging and half-built structures. If you put a malfunctioning battery in a poorly ventilated cabin, the gases have nowhere to go.
The rulebook is moving, as regulators wake up to the severe threats posed by lithium-ion fires. ISO 3941:2026 added a Class L category especially for these fires, because they behave unlike the Class A, B and C events that fire crews train for. They resist being extinguished and can reignite hours later. Guidance from the Health and Safety Executive, HSG168, Fire Safety in Construction, now names lithium-ion batteries as a significant ignition source.
Insurers have noticed too. Aviva asks sites to ban unattended charging and keep it clear of anything combustible. Zurich wants battery risk written into the site fire management plan. When insurers start writing clauses around an issue, it becomes a commercial as well as a safety concern.
What you can do before getting on site
Fortunately, good practice is not complicated. Check a battery before use, and if it is damaged, swollen, discoloured, hot, hissing or giving off an odd smell, take it out of service and report it. Charge the battery inside the 15-30°C window, and never charge it in direct sunlight or in a hot van. Do not leave anything charging unattended or plugged in overnight without someone watching it.
The British Safety Council recommends banning unmanned charging outright. Never charge a damaged battery, stick to the charger that came with the tool, and PAT test any third-party charger before use.
That’s hardly a gruelling checklist. The difficulty lies in getting a rotating cast of trades to do it every day without being continually told.
A job for the site manager
This is where a job site’s overall culture and working practices come into the equation.
Charging needs a proper home: a ventilated, segregated spot, clear of cabins and stores, and managed in line with the logic that's already applied to gas bottles and fuel bowsers. The EFFC’s 2024 safety alert says the same; charge in designated locations rather than open working areas or offices. Protocols should be widely advertised and closely followed; they’re not just documents for filing away in induction packs.
Managing temperature is now a year-round job: the Met Office says summers as hot as 2026’s are roughly 70 times more likely than in a pre-industrial climate, so planning storage around the weather is no longer optional.
Above all, people need to feel comfortable with flagging that a battery looks wrong. On a fragmented site, that permission to speak up has to be widely understood and communicated from the top.
Culture is the key
The suppression unit in that overnight fire did exactly what it was built to do. It bought the crew time and kept a bad night from becoming a catastrophe. But the real measure of a site isn’t the kit on site. It’s up to individuals whether a battery goes on charge when it’s damaged, or gets stuck in a hot cab or stays running after hours. People make those choices, and they do so within a workplace and leadership culture.
So, ask yourself: does the newest subcontractor through the gate on Monday morning know who to speak to when a battery looks wrong? And do they believe something will be done about it when they put up their hand?
Matthew Partridge is head of product development at Armorgard UK
