Portable Generator Safety on Site — Carbon Monoxide, Fuel and Electrical Risks (2026)

Carbon Monoxide — The Hazard That Kills First

Carbon monoxide (CO) is the single most serious and frequently fatal risk with portable generators, so it comes first. Every petrol and diesel generator produces CO in its exhaust. CO is colourless, odourless and tasteless — you cannot see it, smell it or taste it. It builds up silently, and in a confined or poorly ventilated space a running generator can raise CO to lethal levels within minutes. Several deaths in the UK each year involve generators and other fuel-burning equipment used in the wrong place.

The rule is simple and absolute: never run a generator indoors, in a garage, in a basement, in a partially enclosed space, in a tent, or near doors, windows or air intakes. "Partially enclosed" matters — opening a roller door or a window does not make a garage safe. Exhaust gas drifts back in, pools, and concentrates. Even outdoors, position the generator well away from any opening into an occupied building or vehicle so fumes cannot find their way inside.

Run generators only outdoors, in a genuinely well-ventilated open area, with the exhaust pointing away from people and from any building. Fit and use a CO alarm wherever there is any chance of fumes reaching a work or rest area — they are cheap and they save lives. Make sure everyone on site knows the early symptoms of CO poisoning so they can act before it is too late:

• Headache — often the first and most common sign
• Dizziness and confusion
• Nausea and vomiting
• Breathlessness
• Drowsiness, loss of consciousness and collapse

If anyone develops these symptoms near a running generator, get them into fresh air immediately, shut the generator down, and call 999 if symptoms are serious or do not clear quickly. CO poisoning can incapacitate a person before they realise what is happening, which is exactly why prevention — running the machine outdoors, well clear of openings — is the only reliable control.

Electrical Risks

A portable generator is a live electrical source and must be treated with the same respect as a mains supply. The single most dangerous mistake is back-feeding — connecting a generator into a building's fixed wiring through a socket or improvised lead so it powers the property. This is illegal and extremely dangerous: it can energise the incoming supply network and electrocute anyone working on it, and it bypasses the protection built into the installation. Never connect a portable generator to a building's wiring. If a property genuinely needs standby power, that requires a properly installed changeover switch fitted by a competent electrician.

For normal site use, follow these electrical controls:

• RCD protection: Use proper residual current device (RCD) protection on outputs so a fault trips the supply before it harms anyone.
• Earthing and bonding: Ensure the generator is correctly earthed and bonded in line with the manufacturer's instructions and the relevant standards for the type of unit.
• 110V on construction sites: Where appropriate, use a 110V centre-tapped-to-earth supply with yellow site connectors, which is the standard for tools on construction sites and limits shock voltage to 55V.
• Suitable cables and connectors: Use leads rated for the load and the environment, keep connectors dry and off the ground, and never run damaged or taped-up cables.
• Inspect before use: Check leads, plugs and the generator's outlets for damage, wear and water ingress before every use.
• Do not overload: Add up the load and keep it within the generator's rated output. Overloading causes overheating, voltage problems and equipment damage.

Fire and Fuel — DSEAR

Petrol and diesel are highly flammable, and storing, handling and using them brings you under the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR). Petrol vapour in particular is heavier than air, spreads along the ground and can be ignited by a spark, a hot surface or static from several metres away. The combination of fuel, a hot engine and a naked flame is how generator fires start.

Control fuel and fire risk with these measures:

• Cool before refuelling: Turn the engine off and let it cool down before you refuel. Never refuel a hot or running engine — spilled fuel on a hot exhaust ignites instantly.
• No ignition sources: No smoking, no naked flames and no spark-producing work near the generator or fuel.
• Approved containers: Store fuel only in approved, labelled containers, away from ignition sources, away from the public, and not in occupied or confined spaces.
• Mop up spills: Clean up any fuel spill immediately and let vapour disperse before restarting.
• Beware static: Static discharge can ignite petrol vapour during pouring — keep the container in contact with the filler where possible and avoid plastic that can build a charge.
• Keep a suitable fire extinguisher (CO or dry powder) within reach of the generator.

Burns and Mechanical Risks

Generators run hot. The exhaust, silencer and engine block reach temperatures that cause serious burns on contact, and they stay hot for some time after shutdown. Keep the hot surfaces away from anything flammable, and warn anyone working nearby. Moving parts — cooling fans, belts and the recoil starter — need guards kept in place; never run a unit with a guard removed.

Site the generator on firm, level ground so it cannot tip or vibrate its way into an unstable position. A generator that topples can spill fuel, break leads and injure people. Make sure it is stable before you start it and check it periodically while it runs.

Noise, Weather, Security and the Public

Generators are loud, and prolonged exposure can damage hearing — provide hearing protection where noise levels are high and consider quieter or acoustically housed units near occupied buildings or events. Protect the unit from the weather using a purpose-made enclosure that still allows adequate ventilation and exhaust dispersal; never improvise a cover that traps fumes or heat.

Site the generator away from the public and secure it against theft, which is common with portable plant. Never leave a running generator unattended where children or members of the public can reach it — hot surfaces, fuel and live electrics are an obvious danger to anyone who does not understand them. Barriers, signage and a controlled exclusion zone around the unit are sensible on busy or public-facing sites.

Your Duties — PUWER, Risk Assessment and Maintenance

A portable generator is work equipment, so the Provision and Use of Work Equipment Regulations 1998 (PUWER) apply. In short, the equipment must be suitable for the task, in good working order, properly maintained, and only used by people who have the information, instruction and training they need to use it safely.

Put the following in place:

• Risk assessment: Assess the specific job — siting, ventilation, fuel handling, electrical load and who is nearby — before the generator goes on. CO and fire should be front and centre.
• Operator information and training: Make sure whoever runs the generator understands safe siting, refuelling, the back-feed prohibition and the signs of CO poisoning.
• Maintenance: Keep the generator serviced in line with the manufacturer's schedule — exhaust integrity, guards, leads and RCDs all matter.
• Pre-use checks: Inspect fuel lines, leads, guards, the exhaust and the siting before every use, and log it.

Quick Reference: Generator Hazards and Key Controls