Petroleum - Making Tanks Safe
This advice is designed to provide basic guidance to traders. It is not a complete or authoritative statement of the law.
Where any underground petrol tank or compartment is permanently taken out of use it must be rendered safe by one of the following methods:
Tanks to be abandoned in place
Any tank to be abandoned in place should be rendered safe
1. by filling with cement slurry using the following procedure.
- a) Drain back all pipelines associated with the tank and remove all residual petrol
- b) the tank must then be ‘bottomed out’ which involves the removal of that quantity of petrol and deposits which remain below the pump suction pipeline, using a hand pump or a flame-proof electrical pump. This procedure should be performed by a specialist contractor
- c) the atmosphere in the tank must inerted by means of nitrogen, nitrogen foam or carbon dioxide (see guidance on these inerting methods in HSE Guidance Note CS 15)
- d) disconnect all pipework entering the tank via the tank lid. Flush through and cap at each end all pipelines previously connected to the tank or compartment
- e) remove the tank lid. (It should be remembered that this can be a hazardous exercise unless great is care taken.) In the case of old tanks without tank lids the suction pipe should be unscrewed leaving a hole approximately 75mm through which slurry of a thin consistency can be poured
- f) the area surrounding the tank as far as boundaries permit should normally be classed as a hazardous area whilst filling the tank is taking place and all necessary precautions should be taken to prevent any source of ignition.
- g) fill the tank with 20 to 1 mix of concrete slurry. Wherever possible the slurry should be assisted to the extremities of the tanks by means of a vibrating device. (It is important to remember (f) above). It is essential that a Petroleum Officer of the Trading Standards Service is in attendance when the slurry fill takes place. Only when the slurrying has been completed to the satisfaction of the Petroleum Officer is the manhole chamber to be filled with concrete.
2. by the use of RG22 HYDROPHOBIC HARD FOAM. This is a specialist process and can only be undertaken by an appointed contractor.
Removal of tanks from the ground
Any tank to be removed should be rendered safe before excavation work starts.
For a tank without leaks the following initial procedure should be followed
- a) drain all pipelines associated with the tank and remove all residual petrol
- b) the tank must then be ‘bottomed out’ which involves the removal of that quantity of petrol and deposits which remain below the pump suction pipeline, using a hand pump or a flame-proof electrical pump. This procedure should be performed by a specialist contractor.
- c) fill the tank or compartment with water to ensure a liquid seal
- d) disconnect all pipelines (except vent pipes) and add water to the tank or compartment until clear water appears at the vent pipe opening
- e) cap or blank off all openings to the tank or compartment
- f) flush through and cap at each end all pipelines previously connected to the tank or compartment.
Excavation work should be carried out with the tank in the filled condition and with suitable precautions to avoid sparks. When the tank is ready for lifting any water used should be emptied and all openings immediately closed. Water should be disposed of by a hazardous waster disposal contractor.
Alternatively the tank may be rendered gas free by the internal application of an inert gas by a competent person.
- a) Tests by a competent person should be carried out to determine if the tank is free of flammable vapours. If so, a gas free certificate should be issued.
- b) If a tank is certified as being gas free of flammable vapours it may be taken out of the ground within 24 hours of the issue of the certificate.
- c) Points (1), a and b should be adhered to if this method is chosen instead of water fill.
For a tank with leaks, all residual petrol should be removed, and the tank ‘bottomed out’ (see paras 1(a) and 1(b) above) and the atmosphere in the tank inerted by means of carbon dioxide, nitrogen or nitrogen foam. (See guidance on these inerting methods in HSE Guidance Notes CS 15). Inerting should be maintained during the excavation process any fault in the tank shell should be sealed as soon as it is exposed and the atmosphere in the excavation should be monitored throughout the process in case of leakage of inert gas or of the presence of a flammable atmosphere arising from petrol leakage.
Any excavated tank should be indelibly marked on two sides with the words PETROL - HIGHLY FLAMMABLE in letters not less than 50mm high and should be water filled or remain inerted, as appropriate, pending disposal.
Disposal of tanks
Any tank which has been removed from its excavation should be disposed of safety as soon as possible. Preparation for and removal by road should be in accordance with the provisions of the current legislation in force at the time.
The person responsible for removal of a tank from a filling station should ensure that the recipient of the tank is made aware of the tank’s previous use and of the need to take adequate precautions against fires and explosions when dealing with it.
Cleaning or demolition of any tank on site should not take place without the agreement of the appropriate authority.
The location of any abandoned tank should be recorded in the site register and brought to the attention of any person who subsequently becomes responsible for the site.
Further the Trading Standards Service should be made aware of the final destination of any tank which has been removed from the ground.
Alternative use of petrol tanks
The tank may be used for the storage of diesel or gas oil providing the petrol tank has had all residual of petrol removed from it, and been ‘bottomed out’ (which involves the removal of that quantity of petrol and deposits which remain below the pump suction pipeline, using a hand pump or a flame-proof electrical pump.) This procedure should be performed by a specialist contractor.
The tank must be filled totally in order to dispel any petroleum vapour. It is important to remember to drain down the pump and pipelines thereby removing all petrol before introducing an alternative fuel.
Notification to the licensing authority
The Petroleum Officer of the Trading Standards Service must be advised on which course of action it is proposed to take to render a decommissioned tank safe and have the opportunity to be in attendance when tanks are filled.
For further details please contact your local Trading Standards Office.
120897 ISS 1.
Primary Authority Partnerships
Reviewed November 2010
B/pet/047/003 November 2002