Author : Douglas Leech, Technical Director, Chemical Business Association
12 August 2022
When it comes to offloading during chemical deliveries, things can and do go wrong. One incident that may occur – with potentially disastrous consequences – is the inadvertent filling of a tank with the incorrect chemical.
The chemical industry typically delivers bulk solutions to ‘end users’ storage tanks via a common 2” BS10 Table ‘D’ flange inlet. However, as the four-bolt configuration is universal, it substantially increases the potential to misconnect.
Additionally, although there can be extensive operating procedures implemented to prevent delivery of incompatible chemicals into the wrong tanks, the task is still performed by people meaning that, despite training and various control measures, there is room for human error.
One substance that is often implicated in crossover incidents is sodium hypochlorite, which is highly reactive. The list of substances with which hypochlorite is incompatible is substantial – among others, it reacts explosively with ammonium salts and violently with acids and reducing agents to emit, in most cases, gaseous chlorine and sufficient heat to generate steam that could cause catastrophic tank failure.
Whilst there is limited reliable recent data on the frequency of cross-delivery of hypochlorite, a report published by the Health and Safety Executive (HSE) in 2000 indicated more than 200 incidents resulting from either the mixing of incompatible chemicals with hypochlorite, or errors where a driver offloaded into the wrong tank. Since that report was published there has been a conscious effort to increase control measures in relation to the offloading of chemicals, specifically in the same location as sodium hypochlorite tanks.
Unique solution to inherent risk
One of the challenges that companies encountered when offloading chemical deliveries were the couplings used at installations. As already mentioned, the chemical industry typically delivers bulk solutions via a common 2” BS10 Table ‘D’ flange connection in the UK.
To address this challenge, a collaborative approach was launched by the CBA, the Chemical Industries Association (CIA) and Water UK to find a solution to mitigate the risk of hypochlorite crossover during discharge. It was determined that a unique coupling could resolve the problem as it would not entail excessive costs to suppliers or customers. In addition, it could be introduced in a staged manner that would both enhance safety but also allow the costs and risks to be managed sustainably. The result was a modified 2” Table ‘D’ flange design.
The modified coupling design can be applied to the customer’s tank delivery flange, both ends of the hypochlorite delivery hose, the delivery end flanges from dedicated bulk hypochlorite tanker fleet, all hypochlorite production site bulk storage tanks, as well as other bulk hypochlorite storage tanks.
By utilising the unique coupling, it would become impossible to deliver hypochlorite to any tank other than those designated for hypochlorite, or to deliver any other bulk chemical to a sodium hypochlorite tank.
Code of Practice
Following the design of the modified coupling a Code of Practice, developed by the CBA, the CIA and Water UK, was published August 2018. The aim of the Code was to increase the level of safety for all persons involved in the loading and unloading of sodium hypochlorite via bulk tanker or tank container.
The Code defined the coupling, stating that it would be used for all new installations, and upon refurbishment of existing installations. The Code allowed existing installations to utilise a specific locakable ‘temporary’ assembly, pending permanent modification of the facility. This was further caveated that the use of the coupling should be ‘phased in’ as soon as reasonably practicable, but no longer than five years from adoption of the Code. The deadline therefore being August 2023.
The HSE collaborated with the parties in producing the document and endorsed the Code as it follows a sensible and proportionate approach to managing health and safety.
About the author:
Douglas Leech is the Technical Director of the Chemical Business Association based in Crewe. He joined the association in 2003 following over twenty years in the product formulation sector in both health & safety and R & D roles. He is responsible for providing advice and assistance to member companies on legal, regulatory and compliance issues. Douglas was involved in major hazards in both operational, training and advocacy roles in the UK and Europe. He participated in the expert group where the harmonisation of Seveso with the CLP regulations was debated over a number of years to provide advice to the European Commission prior to the formulation of the new Seveso III directive.
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