Marina Silva looks at incidents and accidents that occurred as a result of insufficient secondary containment and reviews standards and legislation pertaining to chemical protection
Tanks and drums containing hazardous and flammable liquids require secondary and tertiary protection to prevent potential accidents, such as the Buncefield fire in 2006. Lessons learned from that accident were translated into effective and practical guidance that industry would implement as rapidly as possible. This guidance, titled Safety and environmental standards for fuel storage sites (Part 42, p 16), suggests that insufficient secondary containment contributed to the accident progression and states: “Bund wall and floor construction and penetration joints should be leak-tight. Surfaces should be free from any cracks, discontinuities and joint failures that may allow relatively unhindered liquid trans-boundary migration. As a priority, existing bunds should be checked and any damage or disrepair, which may render the structure less than leak-tight, should be remedied.”
The EU Seveso II Directive holds a database of reported chemical related accidents and near misses of its member organisations. In July 1999, 16.561 tonnes of 30% solution of sodium cyanide at a top-tier COMAH site was released through a leak in the tank to its bund. Of that quantity only 4.260 tonnes were recovered with the remaining material lost to the ground and water. Recommendation again called for improvements to the secondary containment area. The entry does not state what level of protection this bund had if any, but it can be assumed that since three quarters of the leaked material escaped the bund, the protection was either not there, its chemical resistance was insufficient, or this protection developed cracks allowing for the chemicals to seep through the bund.
National codes of practice
Following dangerous occurrences varying in scale from minor near misses to those with catastrophic consequences, many countries have adopted codes of practice directed at installing and maintaining suitable secondary containment. US Environmental Protection Agency (EPA) for instance refers to stationary tank bunds in the Resource Conservation and Recovery Act (RCRA) Subpart J, Tank Systems (40 CFR 264. 193). “Secondary containment systems must be: (b, 1) Designed, installed, and operated to prevent any migration of wastes or accumulated liquid out of the system to the soil, ground water, or surface water at any time during the use of the tank system; and (b, 2) Capable of detecting and collecting releases and accumulated liquids until the collected material is removed.” To meet these requirements, the secondary containment area must be: (C, 1) “Constructed of or lined with materials that are compatible with the waste(s) to be placed in the tank system[…]” and (e, 1, iii) “free of cracks or gaps”. In the UK, Control of Pollutions Regulations 2001 also states that “the container must be situated within a secondary containment system which satisfies the following requirements […] (c) its base and walls must be impermeable […]”.
Secondary containment areas are typically constructed using concrete, because it is cost-effective and provides good structural strength. However, due to its porosity, concrete can be easily permeated and has poor chemical resistance, making it susceptible to deterioration through chemical attack. In addition, concrete is highly prone to cracking due to substrate movement and freeze-thaw cycles.
Barrier coatings for secondary containment areas
As concrete does not address the requirement for chemical resistance, an additional barrier atop is needed to prevent potential spillages from permeating the secondary containment area. Over the years, a variety of solutions have been trialled, from bitumen based paints to epoxy resin based systems. The right solution would depend on the type of media stored within the tank, size of the containment area, expected traffic and weather conditions, among others.
Where the highest chemical resistance is required in case of extremely aggressive chemicals, such as concentrated mineral acids, alkali, amines and alcohols; solvent-free epoxy novolac resin based coatings are typically specified. The drawback of these coatings, however, has long been associated with the very feature that made them chemically resistant - their rigidity. The chemical reaction between the base and solidifier creates an almost impenetrable “physical barrier”. Subsequently, once hardened and cured, these epoxy systems become completely liquid-impermeable and will have excellent resistance to immersion and exposure to a wide range of oil and chemical spillages. Rigidity of these coatings, however, also makes them inflexible and not best suited for heavy trafficked areas or in cases where the underlying concrete develops cracks.
Concrete can develop cracks for many reasons, from excessive loading, to thermal expansion/contraction or during freeze/thaw cycles which lead to the concrete’s movement and settlement. A rigid coating would crack with the concrete, thus terminating chemical protection in case of a spill. Recent advancements in polymer technology have resulted in the development of a hybrid epoxy coating, which combines high cross-linking with rubbery domains in the polymer chain, giving the coating a desired degree of flexibility.
New material development
One of the recently introduced coatings to successfully incorporate these features comes from Belzona Polymerics Ltd and is known as Belzona 4361. To determine the coating’s crack-bridging abilities, Belzona 4361 was first tested for elongation, measured in accordance with ASTM D412. When cured at 20°C/68°F, Belzona 4361’s residual elongation was recorded at 20%, which would be sufficient to bridge a typical crack. To ensure the coating maintains its flexibility at low temperatures, a mandrel bend test in accordance with ASTM D552 was also performed, resulting in a pass at temperatures down to 0°C/32°F.
To further test this coating’s crack-bridging abilities, Belzona 4361 was submitted for a long-term testing at the University of Stuttgart, Germany. The university carries out testing to award a German Federal Water Act (WHG) Approval which is part of a German water law for protecting surface water and groundwater. Only chemical containment coatings with WHG Approval can be used in areas where strict regulations are in place, in order to protect ground water against chemical pollutants. The testing takes two years to complete and consists of a combination of crack-bridging, chemical resistance and ageing tests. Crack-bridging tests are first performed by creating a crack within the concrete and ensuring the coating remains intact. This is followed by chemical resistance testing where the chemical is positioned onto the test coating so that the crack in the concrete is directly underneath. Signs of chemical attack are visually observed, in particular to see if the chemical reagent attacks the test coating severely enough to penetrate through the crack due to the reduction in film thickness over the crack.
To replicate real life exposure or ageing, the coated test blocks are stored in damp sand and placed outdoors. After six months and two years respectively of aging exposure, crack-bridging and chemical resistance tests are repeated. Belzona 4361 passed the crack-bridging and chemical resistance tests after six months of aging exposure, which will be repeated again to complete the two year’s testing. WHG presents rigorous independent testing and the results will be equally relevant in Europe and globally.
Chemical resistance was tested by coating rods and immersing them in specified chemicals for a period of up to 12 months. The table below illustrates obtained results for some of the tested chemicals.
Chemical Belzona 4361 length of resistance
93% Sulphuric Acid 52 weeks and beyond
37% Hydrochloric Acid 52 weeks and beyond
43% Phosphoric Acid 4 weeks
25% Phosphoric Acid 39 weeks
10% Acetic Acid 1 week
2% Acetic Acid 52 weeks and beyond
25% Ammonia 4 weeks
Ethyl Acetate 52 weeks and beyond
Ethanolamine 1 week
Oil, Petrol and Diesel 52 weeks and beyond
Ethanol 52 weeks and beyond
Methanol 17 weeks
Table 1. Chemical Resistance of Belzona 4361
The coating is perfectly suitable to resist aggressive chemicals, as protection is only required to last until the leaked chemical can be recovered from the bund. Best practice reports in some countries do not specify a universal length of time the coating needs to resist the spilled chemical and some documents state 72 hours as an acceptable length of protection, see the U.S Environmental Protection Agency proposal, 40 CFR 112.7(c).
Chemical protection in action
Following its introduction in 2015, Belzona 4361 has been applied to protect the most critical assets. A secondary containment area in a Missouri, U.S. power plant was coated with Belzona 4361 after the existing chemical protection had failed. The bund in place to contain spillages from a 93% sulphuric acid tank experienced splashes, spills and poor clean-up procedures, in addition to movement which resulted in small gaps forming between the floor and bottom of the wall inside the containment area.
The power station has already been using a variety of Belzona materials ever since six years ago Belzona Gateway Inc, the local Belzona Distributor, solved a major leak problem bringing their water treatment plant back in service. It then came as no surprise that this long standing customer turned to their local Belzona representative for a solution. After assessing the problem, Belzona Gateway proposed to use Belzona 4361 due to its excellent chemical resistance, flexibility and good adhesion facilitating long-term sealing between the bund’s wall and floor. The application was carried out in March 2015 and inspected recently, revealing that the Belzona protection was fully intact.
100% solids epoxy materials adhere well not only to concrete, but can be successfully used to protect a metal substrate from the chemicals. Added flexibility of the coating expands and contracts in sympathy with the underlying metal substrate. This second case study comes from China, where Belzona 4361’s chemical resistance and flexibility were put to the test when it was used to line two acid tanks at an oil field’s power plant. The acid tanks contain 37% hydrochloric acid and were previously protected with an elastomer lining. In winter, when the plant transferred the hydrochloric acid from cold environment (<-0°C/32°F) to room temperature (>20°C/68°F), the dramatic temperature change caused the existing elastomer lining to crack and, as a result, the tanks started leaking. Belzona 4361 was used to line two tanks in October 2015 and the client requested another two tanks to be coated in 2016.
Utilising coatings which provide chemical resistance as well as crack-bridging ability is crucial to both comply with relevant standards and to guarantee lasting protection from spills. As the industry keeps improving the safety of their operations, material manufacturers need to keep up and continue to innovate by utilising novel raw materials. Of course, provision of an adequate secondary containment area is only one of the many improvements that can be done to manage hazards and minimise risks. Some of the other areas to consider include system automation and software, with leak detection technologies and alarm sounding. Such systems can dramatically reduce human error, which was found to be a major contributing factor in the progression of several accidents described in the Seveso Directive. Enhancing safety protocols will ultimately ensure that accidents such as Buncefield do not happen again.
Marina Silva si with Belzona Polymerics Ltd.
1. Broder, M.F., Technical Report: Building a Secondary Containment System, United States, Tennessee Valley Autority, 1994
2. Rivers, K., Buncefield Standards Task Group Final Report: Safety and Environmental Standards for Fuel Storage Sites, http://www.hse.gov.uk/comah/buncefield/bstgfinalreport.pdf, 2007 (Accessed on 1 January 2016)
3. European Commission, The Seveso Directive, http://ec.europa.eu/environment/seveso/, 2015 (Accessed on 10 December 2016)
4. 40 CFR 264.193 – Containment and Detection of Releases, https://www.law.cornell.edu/cfr/text/40/264.193, 2015 (Accessed on 20 December 2016)
5. Grainger, W W, Secondary Containment Requirements: Quick Tips, https://www.grainger.com/content/qt-secondarycontainment-requirements-182, 2015, (Accessed on 20 December 2016)
6. Water Resources, England, The Control of Pollution (Oil Storage) (England) Regulations 2001, http://www.legislation.gov.uk/uksi/2001/2954/pdfs/uksi_20012954_en.pdf, 2001, (Accessed on 20 December 2016)
7. NCC Bund Lining, Bund Lining Materials, http://www.bundlining.co.uk/BundLiningMaterials.html, 2014 (Accessed on 10 January 2016)