Demolition of Petroleum Tanks

DEMOLITION OF PETROLEUM STORAGE TANKS at the Mobil Gas Depot, Coventry

By A. Leese, Q.F.S.M., M.I.F.E., Chief Fire Officer, City of Coventry.

In early April, 1971, a request was received by the City of Coventry Fire Brigade from a local demolition contractor for advice as to the Fire Safety Precautions to be adopted in the demolition and removal of petrol and oil stofage tanks on a former petroleum distribution depot at Torrington Avenue, Coventry.

The site covered some 4! acres with two 225,000 gallon petroleum storage tanks, two 65,000 gallon petroleum storage tanks, six 65,000 gallon oil tanks, all ancillary pipework, valves and fittings. The petroleum tanks were vertically placed each in its own bund; the gas oil tanks were horizontally placed, bunded in pairs. When the depot was operational it was supplied by rail tankers from the depot sidings; these sidings running off the main Birmingham to Coventry line. The distribution from the depot was by road tankers, loaded from an overhead distribution system.

The depot had ceased to operate some twenty months previous, due to the installation of an underground pipe-line supply running from the oil terminal in the Thames Estuary to a new distribution depot at Kingsbury, Warwickshire. The petrol em tanks had been subject to a detection of inflammable vapour test, and a monthly certificate was issued. When operational the site was licensed under the Petroleum (Consolidation) Act, 1928. The City of Coventry Fire Brigade acting for the Local Authority as the Licensing Agent.

It was, therefore, agreed that in consultation with H.M. Factory Inspectorate, advice would be given to the contractor on the hazards involved, and the method to be adopted in dealing with the empty tanks. The City of Coventry Fire Brigade to provide practical assistance when required.

The agents who placed the contract with the demolition contractor laid down specifications which they requested the contractor to comply with. These included the requirement to comply with all necessary regulations and notices to be given to the Factory Inspectorate and the Fire Brigade.

For the contractors part he was fully aware of the task before him and was eager that all safety standards and provisions were adhered to.

A site meeting was convened in April, 1971; present were representatives from H.M. Factory Inspectorate, Construction Division, the Contractors, and the City of Coventry Fire Brigade.

H.M. Factory Inspectorate, in consultation with the Fire Brigade representatives, laid down the safety precautions as follows :1. All pipework and supplementary equipment would be removed first by unbolting all the joints. The pipework to be flushed with a non-toxic, non-flammable

liquid to reduce and disperse vapours or any residues. Explosive meter tests to be made before work commenced. 2. Before work started on the tanks a gas free certificate would be issued by an Industrial Chemist. If this could not be produced, then the tanks would be steam cleaned until such time as an inert atmosohere existed and the certificate could be provided. 3. If hot cutting was the method favoured the tanks would be filled and kept filled with high expansion foam. 4. The roof of the tanks would be removed first. 5. During the operations, periodic tests with an explosive meter would be taken to ensure inert atmosphere. 6. Fire applances and crews would be standing by during these operations. 7. A qualified Safety Officer would be permanently in attendance the whole time. 8. In his absence, all safety requirements made by the Brigade would be carried out as if by himself.

A of Technical Data Note No. 18 on the Repair and DemolitIOn of Large Storage Tanks, issued by the Department of Employment and Productivity, H.M. Factory Inspectorate, was handed to the contractor at the conclusion of the meeting.

There. followed a further site meeting, present were representatIves of the contractor and the City of Coventry Fire Brigade. The contractor stated that he had agreed with the Factory Inspector that hot cutting would be the method used. The format was finalised as follows :_ (a) Work on site would commence on Wednesday, 26th May, 1971, when railway lines and pipework would be dismantled. (b) Vent caps on all tanks, together with control valves would be unbolted and removed. (c) Inspection covers on top of the tanks would also be unbolted and removed. (d) Before and during these operations the Industrial Chemist who would be permanently on site, would carry out tests.

The demolition of the four large storage tanks requiring the attendance and participation of the Fire Brigade would commence when the above jobs had been completed.

The method of demolition to be as follows :_

Prior to the commencement of work on any of the four tanks, the Industrial Chemist will carry out tests and issue a gas free certificate.

Immediately after issue of this certificate, the Brigade will fill the tank with high expansion foam from the base and, in addition, place a layer of high expansion foam about 1ft. deep around the outside of the tank in the bund area.

Hot cutting of the tank top will then commence.

A continuous input of foam into the tank will take place during cutting operations.

When the top has been removed, the tank will be kept topped up with foam whilst the base is cut, after which the tank will be pulled over.

The Industrial Chemist to take readings inside the tank from time to time whilst cutting is in progress. Fire Service personnel, who were to be present throughout the operation, were briefed as to the task and were made fully aware of all safety requirements, both of personnel and others.

Compressed Air Breathing Apparatus and proximity suits were carried on the appliances attending.

Access for additional appliances and other emergency vehicles to be maintained throughout the operation.

On Wednesday, 2nd June, 1971, crews with a Pump and Foam Salvage Tender attended the site to fill the tanks with high expansion foam and provide fire cover.

A Waiter Kidde P.500 Portable Hi-Expansion Foam Generator capable of producing some 5,000 cubic feet of foam per minute was placed within the bund approximately 10 feet from the base inspecting cover of one of the 225,000 gallon tanks. A three foot diameter canvas tube was attached to the generator and to the inspection hatch at the base of the tank.

The Hi-Expansion Generator was placed as close to the tank as possible for the following reasons :(a) To give the shortest delivery line to overcome the back pressure of the foam inside the tank. (b) The area of ventilation in the top of the tank was of a far less proportion to the surface area of foam being introduced (back pressure). (c) The short canvas delivery tube could be controlled by the generator operator and two men when the Hi-Expansion Unit was shut off. (d) It has been found that to lift Hi-Expansion Foam within large tanks by base injection is proportioned to the distance the unit is away from the tank. (e) When hot cutting takes place, protection has to be given to the generator and the delivery tube from hot metal dropping from above, therefore, the nearer the generator the less length of delivery tube to be protected.

The above were actual practical incidents that were experienced whilst the tanks were being filled. Whilst it may be stated that the tanks could be filled from the top, this was not a practical proposition due to the working space required for cutting, and pockets of vapour could be trapped beneath the roof crown and the inlet manhole due to foam dropping into the tank.

When the tank was two-thirds full it became obvious that the displacement of air and vapours by the foam in the tank was having the desired effect. Petroleum vapours could be detected by smell and were being forced out of the tank through all the top outlets. Readings were taken throughout this process, and when foam poured out through the top outlet in the crown of the tank a final reading was taken and a gas free certificate was issued. Cutting was commenced at once around the top .of the tank, the roof being cut into sections and allowed to fall into the tank.

When the top was completely removed the contractor cut around the base of the tank. Readings were constantly taken and the tank was kept topped up with foam.

Following the final cut in the base of the tank, a steel hawser was secured to the tank, and it was pulled over by a tractor.

The same procedure and precautions were taken with all the tanks until they were opened and pulled over.

It would be untrue to say that the operation was without incident, two small fires did occur but were quickly dealt with by the hose lines laid out for such a purpose. One incident involved a small area of grass that was ignited by hot metal being blown by the wind for about a hundred yards, the second incident occurred when a small area of soil beneath a pipeline drain valve ignited when the valve was being cut off. These were two isolated incidents which were quickly dealt with away from the main area of operations, and they did not place any persons or property in any danger.

Whilst the successful conclusion of such a hazardous operation can be looked upon with a certain amount of satisfaction, it can only be successful with the co-operation and willingness of all concerned to take the necessary precautions.

Although guidance can be given in circulars which relate to particular hazards, it is only the personal approach in ensuring that these standards are strictly adhered to. In this instance the site agent and contractor were more ,than willing to play their part, and the presence of personnel and appliances throughout the cutting operations made them aware of their task.