Generators and carbon monoxide: why they only ever run outdoors

A portable generator is a petrol engine with an alternator attached, and every petrol engine makes carbon monoxide (CO). The NHS includes portable generators in its list of things that can produce carbon monoxide, and warns that turning on vehicle or lawn mower engines in an enclosed space such as a garage can also cause a build-up.

The rule that follows is short: generators run outdoors, away from the building. Here is what the makers and the NHS actually say.

Honda’s rules for running a generator

Honda’s UK safety page for its generators — which covers machines such as the EU10i, EU22i and EU32i — says:

• Never run your generator in a confined or partially confined space, or inside a garage or house, or near open windows or doors. Honda gives carbon monoxide poisoning as the reason.
• Keep the generator at least one metre (three feet) away from buildings and other equipment while it is running.
• Do not enclose the generator in any structure, and keep flammable materials away from it — the exhaust gets hot enough to ignite some materials.
• Always place it on a firm, level surface before you start it.
• Never modify it, and don’t run it with any cover removed.
• If it is stored outdoors, check the electrical components on the control panel before each use: Honda warns that moisture or ice can cause a malfunction or short circuit, which could result in electrocution.
• Do not connect it to a building’s electrical system unless an isolation switch has been installed by a qualified electrician.
• Refuel with care — petrol is extremely flammable and its vapour can explode — and let the engine cool first if it has been running.

Those points are worth reading as a list of things people actually do: running a generator in an open-fronted garage “for the rain”, in a shed with the door open, or on a campsite next to an awning. A partly enclosed space counts.

Why “near open windows or doors” matters

You can be inside a perfectly normal room and still be at risk if a generator outside is running beside an open window or door — which is why Honda names them. Put the generator well away from the house and its doors and windows, and treat Honda’s one-metre clearance from buildings as a minimum.

The symptoms

The NHS explains that carbon monoxide is colourless and doesn’t smell, so you can’t tell it is there. Symptoms include:

• a headache
• dizziness
• feeling or being sick
• feeling weak
• tiredness and confusion
• chest and muscle pain
• shortness of breath
• loss of vision

The NHS notes that symptoms may come and go, and may get better when you go outside and worse when you go back in.

What to do

The NHS advice if you think you might have carbon monoxide poisoning:

1. Stop using the appliance you think is making carbon monoxide, if you can — for a generator, that means switching it off.
2. Go outside into fresh air.
3. Get medical advice as soon as possible, and don’t go back into the affected building until you have.

Call NHS 111 if you think you might have symptoms. Call 999 or go to A&E if you think you or someone else has been exposed and they are finding it hard to breathe, have suddenly become confused, have lost consciousness, feel weak or have chest or muscle pain. The NHS says not to drive yourself to A&E: ask someone to drive you or call 999 for an ambulance.

Carbon monoxide alarms

The NHS recommends a carbon monoxide alarm that makes a loud sound, with one for each room that has an appliance burning gas, oil, coal or wood. An alarm is a back-up, not permission: Honda’s rule is that a generator never runs inside, whatever alarms you have. Search Amazon for carbon monoxide alarms.

The same goes for other engines

Everything above applies to every petrol machine in this guide — the SIP 8 ton petrol log splitter, the STIHL GH 460 chipper, petrol cement mixers and petrol pressure washers. If the job has to happen indoors or under cover, look at a mains or battery machine instead. Battery machines have no exhaust at all: Belle describes its Minimix 150E+ mixer as having no engine emissions.

Before you buy a generator

• Work out how much power you need: see how to size a generator.
• Plan where it will stand when it runs — outside, on firm level ground, a metre or more from walls and well away from doors and windows.
• Plan how you’ll store fuel: see storing petrol at home.
• If you want back-up power for your house wiring, talk to a qualified electrician about an isolation (changeover) switch first.