The UK has been hit with multiple heatwaves so far this summer! Heating oil is probably not even on your mind right now, however it is worth noting that these high temperatures can affect your domestic heating oil if not stored correctly. High heat changes the way fuel behaves, and knowing how to store it properly could save you a lot of hassle, or worse, a genuine safety risk.
Why Heat Is a Problem for Stored Fuel
Fuel, whether it is petrol, diesel, or a pre mixed two stroke blend, is a volatile substance. That means it evaporates and expands more readily as temperatures rise. During a heatwave, ambient temperatures can push stored fuel well beyond the range it was designed to sit at, and this creates several risks.
This applies just as much to a large bulk tank as it does to a small can, though a bulk tank tends to heat up more slowly and then hold that heat for longer once temperatures do rise, since it takes far more energy to warm or cool a large volume of fuel.
Increased Vapour Pressure
As fuel heats up, its vapour pressure increases. This means more of the liquid converts into flammable vapour inside the container. In a sealed can or tank, this build up of pressure can cause the container to bulge, warp, or in extreme cases, fail completely. Vapour escaping into the surrounding air also raises the risk of ignition if there is any nearby heat source, spark, or flame. Bulk tanks are generally fitted with pressure relief valves for exactly this reason, and these should be checked more often during a heatwave to confirm they are clear and working correctly.
Fuel Expansion
Liquids expand when heated, and fuel is no exception. A container that was filled to a safe level in cooler weather may become dangerously overfilled once temperatures spike, leaving no room for expansion. This is why manufacturers always recommend leaving airspace at the top of any fuel container, and why overfilling during a heatwave is particularly risky.
Faster Degradation
Heat accelerates the chemical breakdown of fuel. Petrol can lose its combustibility more quickly in hot conditions, ethanol blended fuels can separate or absorb more moisture, and diesel can be more prone to microbial growth and fuel bug issues when stored warm for extended periods. This means fuel bought or mixed at the start of a heatwave may not perform as well by the end of it if stored incorrectly.
Choosing the Right Fuel Storage Containers
The container or tank you use plays a huge role in how safely fuel can be stored during hot weather.
Use Approved, Certified Containers
Always store fuel in containers specifically designed and certified for the purpose. Look for containers that meet recognised safety standards, as these are built to handle pressure changes, resist punctures, and reduce vapour leakage. Avoid using old drink bottles, unmarked containers, or anything not intended for fuel storage, no matter how convenient it may seem in the moment.
Metal Versus Plastic
Both metal and high density polyethylene plastic containers can be safe options, provided they are approved for fuel use. Metal containers tend to handle heat exposure and UV degradation slightly better over time, while modern plastic fuel cans are designed with venting systems that help manage pressure build up. Whichever you choose, check regularly for signs of wear, cracking, rust, or a failing seal, since heat can accelerate the ageing process of both materials.
Check the Seals and Vents
Many fuel containers include a pressure relief vent or cap designed to release excess pressure safely. During a heatwave, it is worth checking these vents are not blocked, damaged, or stuck closed. A container that cannot vent properly is far more likely to bulge or fail under heat.
Bulk Tanks Fixed on Site
Many businesses and sites store fuel in a bulk tank that is already sited and not something that can realistically be moved or relocated once installed. In these cases, the tank itself does not need to be swapped out, but it does benefit from a few extra checks during hot weather.
Confirm the tank shell shows no signs of bulging, discolouration, or damage, make sure any bund around the base is clear of debris and standing water, and check that vents and relief valves are functioning correctly. A light or reflective coloured coating on the tank exterior also helps reduce how much heat the tank absorbs directly from the sun, which is a useful option for a tank that stays in the same spot year round.
Where to Store Fuel During a Heatwave
Location matters just as much as the container itself.
Avoid Direct Sunlight
Never leave fuel containers sitting in direct sun, even for a short period. A container left on a driveway or in an open trailer can reach internal temperatures well above the surrounding air temperature simply from solar heating. Always store fuel in a shaded area, ideally indoors or under solid cover. For a fixed bulk tank that cannot be moved into shade, a temporary shade sail, canopy, or fixed roof structure built over the top of the tank can achieve a similar effect without relocating anything.
Choose a Cool, Ventilated Space
The ideal storage spot is cool, dry, and well ventilated. A detached shed, garage, or purpose built fuel store away from the main house is usually best. Good ventilation is essential because it allows any leaked vapour to disperse rather than build up in an enclosed space, which reduces fire and explosion risk considerably.
Keep Fuel Away from Ignition Sources
During hot weather, it becomes even more important to store fuel well away from anything that could provide an ignition source. This includes electrical equipment, power tools, boilers, pilot lights, and anything that generates sparks or heat. Even a small increase in ambient temperature combined with a nearby spark source raises risk substantially.
Consider Below Ground or Insulated Storage
For larger quantities, some riders and businesses use insulated storage boxes or bunded tanks that are partially shaded or below ground level, since these naturally stay cooler than surface level storage exposed to direct heat. If you store fuel in bulk, it is worth reviewing whether your current setup provides adequate insulation for summer conditions.
Practical Tips for Safer Fuel Storage in Hot Weather
- Only store the amount of fuel you realistically need for the short term rather than stockpiling large quantities that will sit through the hottest part of summer.
- Leave adequate airspace in every container to allow for thermal expansion.
- Label containers clearly with the fuel type and the date it was filled, so older stock is used first.
- Check containers regularly during a heatwave for signs of swelling, leaking, or damage.
- Move fuel away from windows, glass, or reflective surfaces that can concentrate heat.
- Keep a fire extinguisher rated for flammable liquids nearby, along with a working smoke or heat alarm in the storage area.
- Avoid transporting fuel in a hot car boot for longer than necessary, since vehicle interiors heat up dramatically faster than open air.
- For fixed bulk tanks, increase the frequency of visual checks and valve inspections during extended hot spells, since a tank that cannot be moved needs closer monitoring in place of relocation.
Final Thoughts
A heatwave changes the rules when it comes to fuel storage. What is considered safe practice in cooler months can quickly become a genuine hazard once temperatures spike, whether that risk comes from increased vapour pressure, container expansion, or accelerated fuel degradation. By choosing the right certified containers or tanks, storing fuel in a cool and well ventilated location away from direct sunlight and ignition sources, and only keeping the amount you actually need on hand, you can significantly reduce the risks associated with hot weather fuel storage.
Taking a few extra precautions during periods of extreme heat not only protects your property and equipment but also keeps you, your family, and anyone nearby considerably safer. If you are ever unsure about the condition of your stored fuel or the suitability of your storage setup, it is always worth seeking advice from a fuel safety professional or your local fire safety authority.
Stay cool, stay safe, and always respect the way summer heat can transform an everyday task like fuel storage into a serious safety consideration.