Introduction
This guidance explains the fire and explosion risks that can arise when tanks or vessels that have stored petrol or other flammable liquids are repaired, removed, filled, or demolished.
Under Section 73 of the Public Health Act 1961, the council has powers to require occupiers and owners of premises to take reasonable steps to prevent pollution from petrol tanks.
Serious accidents, including fatalities, have occurred where tanks containing flammable residues were not properly prepared before work began.
Even tanks that appear to be clean can remain dangerous. Water inside a tank can cause corrosion, reduce oxygen levels and create flammable hydrogen gas.
Anyone involved in this type of work should:
- receive appropriate training
- understand the risks involved
- follow safe working procedures
- take all necessary safety precautions
Work should be supervised by a competent person with sufficient experience to ensure it is carried out safely.
Because of the wide variety of products that may have been stored in tanks, it is not possible to provide guidance for every situation. If there is any doubt about the risks, particularly where products are toxic or unstable, advice should be sought from the manufacturer, supplier or another specialist.
Hazards
Flammable vapours can ignite inside a tank and create pressures far greater than most storage tanks are designed to withstand.
Even tanks designed as pressure vessels are not normally designed to withstand an internal explosion.
If an explosion occurs:
- the tank may fail violently
- parts of the tank may be projected as missiles
- flames and hot gases may be released
- burning liquids may be expelled from the tank
These hazards can cause serious injury, death and significant property damage.
Health and safety guidance
The Health and Safety Executive (HSE) publication CS15: Cleaning and Gas Freeing of Tanks Containing Flammable Residues explains the legal requirements and the safety precautions that should be followed when repairing, cleaning, removing or demolishing tanks.
Other authorities you may need to consult
Before work starts, you may need to consult:
- the Health and Safety Executive (HSE)
- the Petroleum Licensing Authority
- your property insurer
Petrol tanks permanently taken out of use
The council's preferred approach is for petrol tanks that are permanently out of use to be removed from the ground and disposed of safely.
Where removal is not practical, the council may allow a tank to remain in place if it is permanently filled with:
- concrete or cement slurry, or
- an approved inert hydrophobic foam
This must be carried out using an approved method.
Permanently removing a petrol tank
Before removal:
- all petrol residues must be removed
- the tank must be made safe using water, nitrogen foam or another approved inert material
- pipework must be disconnected and secured
- safe excavation methods must be used
- smoking and naked flames must be prohibited
Any contaminated water removed from a tank must be disposed of by a registered waste carrier.
Where tanks are transported by road, relevant dangerous goods transport regulations must be followed.
Filling a disused petrol tank
Where a tank cannot be removed, it may be permanently filled with:
- cement slurry
- concrete
- approved hydrophobic inert foam
The tank must first be made safe and the work carried out by suitably qualified contractors using appropriate safety controls.
Temporary methods for making petrol tanks safe
Temporary methods should only be used where:
- the tank will be brought back into use, or
- the tank will be removed or modified within a limited period
The council generally accepts temporary measures for no longer than 12 months.
Approved temporary methods include:
- water filling
- hydrophobic inert foam
- nitrogen foam
Water filling
Where water is used:
- all petrol residues must first be removed
- tank openings and pipework must be secured
- water levels must be maintained to prevent vapour build-up
Nitrogen foam
Nitrogen foam can be used to make a tank temporarily safe.
However, it is not a permanent solution because the foam settles and breaks down over time.
The foam must be checked and replenished regularly, particularly before any work is carried out on the tank.
Hydrophobic inert foam
Hydrophobic inert foam can be used as either a temporary or permanent method of making a tank safe.
Depending on the circumstances, it may be possible to treat the tank without first filling it with water.
Further guidance
Useful references include:
- HSE Guidance Note CS15: Cleaning and Gas Freeing of Tanks Containing Flammable Residues
- The Road Traffic (Carriage of Dangerous Substances in Road Tankers and Tank Containers) Regulations 1992