Sites with licences from the Irish EPA are required to have a bund integrity assessment every three years. The fact that there have been no incidents on the EPA incidence database caused by bund failure shows that the system of inspection is working well.
The EPA’s preferred method of bund inspection for bunds is by hydrostatic testing. This will tell us whether the bund is water tight. However, it will not tell us how the bund will cope with a fire or other hazardous situation. Since many bunds are used to store flammable materials this is a potential risk that many sites may overlook.
The fire at the Buncefield petroleum fuel storage depot in the UK in 2005 provides some valuable insights into how bunds perform in fires and what can to done to improve matters. Specifically, the construction details of joints and pipe penetrations significantly affect the ability of a bund to provide containment in the event of a fire.
Bunds are generally built of reinforced mass concrete cast in sections. To ensure water tightness at the joints between the wall sections, a flexible joint is used (termed a water bar or water stop). This water bar can be plastic, stainless steel or copper. The water stop is placed in the centre of the wall and bridges the two wall sections. In the photo evidence of the blue plastic water stop can be seen on the right (due to cost considerations, most new bunds in the UK and Ireland now use plastic water stops).
The concrete bunds at Buncefield with metal water stops contained the spilled contents of the tanks. However, the concrete bunds fitted with plastic water stops failed as the plastic melted in the heat of the fire.
Other issues that caused a lack of containment were where pipes penetrated the bund wall. Expansion of the pipe in a fire can cause the seal between the pipe and the wall to fail or even rupture of the pipe.
Following an investigation into the aftermath of the fire, revised guidance on bund construction was issued. This included advice on how to assess existing bunds for the ability to withstand a fire and what cost effective action can be taken to upgrade existing bunds to satisfactorily cope with a fire. This advice is detailed in CIRIA 736. It is noted that there is currently no requirement for such fire assessments in Ireland.
Environmental Efficiency would strongly recommended that sites review the resistance to fire of their existing bunds as part of their normal period bund inspection programme. Environmental Efficiency can advise on such inspection and what steps are needed to bring bunds up to the necessary level of fire protection.
The author, Bob Sutcliffe, is a Chartered Engineer & environmental consultant with over 20 years’ experience of bund integrity testing in the UK and Ireland. Bob may be directly contacted on bobsut@enviro-consult.com