PROJECT ON LOSS OF CONTAINMENT POTENTIAL FROM TANKS CONTAINING HAZARDOUS SUBSTANCES

摘要

Losses of containment from tanks have led to a number of serious incidents and accidents. A project was, therefore, initiated within Unit 3 of Land Division of HSE's Hazardous Installation Directorate (HID) to gather information on the potential for loss of containment, and the measures currently in use to mitigate the possible consequences. The work was carried out with a view to identifying benchmarks for simple alarm/automatic protection systems designed to reduce the incidence of tank overfilling, and other protection measures to prevent loss of containment. Thirteen sites - within Wales and the West of England were visited over a 6-month period as part of this project. Sites chosen contained more than 5 fixed tanks storing a variety of substances. Sites with large, complex storage facilities, such as refineries or large chemical plants were excluded. The key findings of this work were: 1. Wide variations existed in standards in design, selection, fabrication, installation, inspection and maintenance of tanks, bunds, alarms, trips, valves, and fittings. Appropriate enforcement action was taken where companies failed to comply with the law. 2. Most of the sites visited had made little effort in carrying out risk assessments on loss of containment. Few had identified safety critical items. 3. In many instances tanks were not fitted with adequate level alarms and trips. The tanks were old and no records existed of these being 'fit for the purpose'. Bunds were also inadequate in size and were constructed of inappropriate materials. 4. Most of the sites visited paid little attention to the inspection, testing and maintenance of isolation valves, pipe work and fittings. Failure of these has in the past lead to loss of containment. 5. On a number of sites, pumps and other items were found to have been located inside the bund where a catastrophic failure of a tank could lead to a serious incident. 6. On many sites no consideration had been given to the use of Remotely Operated Shut Off Valves (ROSOV's), in the event of an emergency. 7. In many instances, separation distances were inadequate, bunds were excessively crowded with tanks, piping had been poorly installed through the bund wall and bunds were cluttered. 8. In most cases housekeeping was poor and there were build ups of rainwater, potentially flammable materials, inside tank and pump bunds. Appropriate design features to prevent loss of containment are discussed. Internal HSE guidance is being prepared for inspectors, giving details of the survey and offering advice on the circumstances where enforcement action would be appropriate. HID's inspection strategy relating to this matter is being developed and the potential for loss of containment from tanks containing hazardous substances may now become one of the issues raised routinely during planned inspections to chemical manufacturing and storage sites.