How do I store petrol and mower fuel safely in summer?

This comes up every summer for mower and strimmer fuel, and the risk is genuinely different from the way most people picture it. Nobody is going to set light to a puddle of petrol. What actually happens is vapour escaping a poorly sealed or overheated container, flowing downhill and along the floor, and finding an ignition source somewhere else entirely — a freezer thermostat, a light switch, a boiler.

Safety

Step by step

1. Use the right container, and only that.Petrol must be kept in a container designed and approved for petrol, in the sizes and materials the regulations allow. Approved metal and plastic cans are cheap and clearly marked. Water bottles, milk containers, old oil cans and unmarked jerry cans are not acceptable — plastics not made for fuel are degraded by petrol and fail without warning.
2. Know that there is a legal limit on quantity.The amount of petrol you may store at domestic premises and the containers it may be kept in are set by regulation, and there are notification requirements above certain quantities. The limits are modest and most people are comfortably inside them with a mower can or two. Check the current figures with your local fire and rescue service or the HSE rather than relying on a remembered number.
3. Store it outside the house, above ground.A detached shed or a well-ventilated outbuilding is right. A cellar, an under-stairs cupboard, an inspection pit or anywhere below ground is wrong, because petrol vapour is heavier than air and pools rather than dispersing. An integral garage is part of the house and a poor choice, particularly if a boiler or freezer lives in it.
4. Keep it cool and shaded.Vapour pressure rises with temperature. A can in direct sun or against a sunlit shed wall builds pressure, stresses the seal and forces vapour past it. Shade, low down, on the cool side of the building, is the place.
5. Open a warm can carefully.Loosen the cap slowly, outdoors, standing upwind, and let the pressure equalise before removing it. A can opened quickly on a hot day can spit fuel. Approved cans have a vent arrangement for this reason — use it if yours has one.
6. Keep it away from every ignition source.Not just flames. Boilers, freezer and fridge motors, light switches, power tool brushes, battery chargers and static from clothing or from pouring fuel are all realistic ignition sources. This is the reason petrol does not belong in the same space as a garage freezer or a boiler.
7. Buy the amount you will actually use.Petrol goes stale, and modern fuel containing ethanol degrades faster and absorbs moisture from the air. Fuel more than a few months old causes hard starting and gumming in small engines. Buying a small quantity more often is both safer and better for the machine.
8. Use a fuel stabiliser for anything stored over a season.If a can or a mower tank is going to sit through the winter, a stabiliser added when the fuel is fresh keeps it usable and prevents much of the gum and corrosion that ethanol-blended fuel causes in a carburettor.
9. Refuel machinery outdoors, on the ground, with the engine cold.Never refuel a hot mower or a running engine, never indoors, and never on a deck or a lawn where a spill soaks in. Let the machine cool, fill it on a hard surface where a spill can be dealt with, and wipe up anything spilt before starting.

Tips

• Ethanol-blended petrol absorbs water from the air and degrades faster than older fuel did, which is why small engines are harder to start after a winter than they used to be.
• Label the can with the date you filled it. Fuel of unknown age is the usual reason a mower will not start in spring.
• Drain or stabilise the fuel in a mower before it goes away for the winter rather than leaving a part tank to gum up the carburettor.
• Never syphon petrol by mouth. Use a proper syphon pump — it costs very little and swallowing or inhaling petrol is a medical emergency.
• If you spill petrol on clothing, change outdoors and let the clothes air outside. Do not put petrol-soaked clothing in a washing machine or a tumble dryer.

Common mistakes

• Keeping petrol in a garage with a freezer or boiler in it — Both are ignition sources at low level, exactly where heavier-than-air petrol vapour collects. It is one of the most common domestic arrangements and one of the most dangerous.
• Storing fuel in an unapproved plastic container — Petrol degrades plastics not designed for it, and the container can fail without warning. Approved containers are inexpensive and clearly marked.
• Leaving a can in the car boot after buying fuel — A sealed hot boot builds vapour pressure and any leak fills the cabin. Take it home directly and unload it immediately.
• Keeping last year's fuel because it looks fine — Ethanol-blended petrol takes up water and goes stale within months. It causes hard starting and gums up carburettors, and the repair costs more than the fuel saved.

Checklist

• Approved petrol container only, correctly labelled
• Outside the house, above ground, well ventilated
• Cool and shaded, never in direct sun
• Upright, cap tight, stored where it cannot be knocked over
• Nowhere near a boiler, freezer, light switch or charger
• Small quantity, bought fresh, stabilised if stored over winter

Questions people ask