Bund inspection and construction standards

Aug 5, 2014 | Building Performance, Bunding and Containment, News | 0 comments

I am involved in bund inspections in both the UK and Ireland and have been struck by the differences in the necessity for bunding, the test methods and the general construction standards.

In the UK, the Oil Storage Regulations 2001 stipulate that bunding is required at non-domestic facilities which store oil in capacities greater than 200 litres. Since the ubiquitous oil drum is 205 litres (used for lubricating, transmission, vegetable and oil waste oil etc.) this regulation will cover the majority of non-domestic sites. Even if oil drums are not present on site, this regulation will also include many sites with oil tanks for boilers or standby generators. This will include most hospitals, schools and colleges outside of the natural gas network. If the Oil Storage Regulations 2001 were not wide enough, bunding is also required at Seveso sites and electricity installations. It would therefore be safe to assume that, in the UK, bunding is going to be required at practically all industrial sites, farms and quarries plus many schools, colleges and hospitals.

In Ireland the requirement for bunding is limited to sites regulated by the EPA, Seveso Sites and those few sites where the local authority has stipulated bunding as part of the planning process. There will be many non-domestic sites in Ireland that do not fall under this requirement, e.g. quarries, and small engineering companies. In addition, as the natural gas network is not as widespread as in the UK, many hospitals, hotels, colleges and schools will have oil tanks and there is no requirement for these to be bunded.

Why there is such a difference is unclear. In the UK, oil pollution incidents have halved in the last ten years since the introduction of the Oil Storage Regulations. These regulations have then clearly had a beneficial impact.

The difference in the inspection requirements also needs examination. Under the UK Oil Storage Regulations an annual inspection by a competent person is recommended, but there is no requirement for this inspection to include hydrostatic testing. In Ireland, sites regulated by the EPA are required to have hydrostatic testing of bunds every three years. However, the requirement for hydrostatic testing is contrary to the advice given in the UK by the COMAH (aka Seveso) Policy Group. This group states that hydrostatic testing is not preferred due to risks associated with tanks instability and corrosion (water can get forced under the seals at the base of the tank).

A hydrostatic test is an unambiguous test, the water level either drops or stays the same. It is therefore a good practical method of bunds inspection. Worries about tank stability and corrosion can be allayed by limiting the depth of the test water to around 200 mm (most tanks will be on a plinth). Where the hydrostatic test is to a low level, a visual inspection of the walls can be easily carried out to complete the job.

A visual inspection of an entire bund (base and walls) cannot be totally conclusive as it is possible that defects can be hidden (either deliberately or unintentionally). At one site visually inspected by the author, the bund failed the inspection due to the presence of an unsealed groundwater monitoring point in the middle of a bunded warehouse floor (probably one of the silliest locations ever). This major defect had been missed in all previous bund inspections by other firms of consultants.

Construction standards should also be considered. My experience is that the bunds in most UK sites are constructed of reinforced mass concrete (or sometimes reinforced brick), usually to BS8007 or CIRIA 163. In Ireland, many bunds are constructed of hollow core blocks, or breeze blocks, sometimes with a render of cement. Block bunds, in our experience, have a significantly higher failure rate than reinforced mass concrete bunds when hydrostatically tested. This is because block bunds are prone to cracking in the walls due to ground movement and also as such blocks are often porous.

A final issue is the poor construction techniques or just misunderstanding of the specifications. I recently carried out a hydrostatic test on a brand new flammable liquid bund. This bund leaked through the wall joints. The builder assured me that the bund was built to BS8007 and proudly showed me photographs of the construction. The reason for the leaks was obvious straight away from the photographs, the reinforcement was not continuous through the wall joints as required by the standard. The filling of the bund with water had caused slight movement in the joint which resulted in the leak. An inspection by a competent person during the construction process would have identified these defects.

Some recommendations are perhaps in order. Firstly, for the UK and Ireland, periodic hydrostatic testing should be required for existing block bunds and the building of new block bunds be prohibited. Secondly, for the UK, consideration should be given to supplementing visual inspections with low level hydrostatic tests. Finally, for Ireland, it is suggested that reinforced mass concrete bunds that have been tested prior to being placed into service should only require subsequent visual inspections (with a less frequent low level hydrostatic test) and that bunding be required for all quantities of oil greater than 200 litres.

The author is a director of Environmental Efficiency which has offices in Bray (Ireland), Birmingham and Lisburn. The author can be contacted directly on bobsut@enviro-consult.com

Some references used in the preparation of this article