In the latest edition of IChemE’s Loss Prevention Bulletin, the Health and Safety Executive (HSE) details the catastrophic explosion of a buffer tank that took place at a Nottingham AD plant in 2017. The article summarises the key causes of the incident, lessons learned to prevent reoccurrence, and the enforcement outcome.

The factors which led to the explosion included:

• process diagrams were not accurate
• a hazard study failed to identify flammable hazards upstream of digester
• the DSEAR risk assessment was inadequate, and
• a Safe System of Work for hot work was inadequate

The causes of these failures seemed to come down to the failure to adequately identify hazards resulting in inadequate risk assessments, and lack of competency on the part of the consultant’s DSEAR qualifications as well as the operator’s legal duties to ensure safe site operation.

Lessons learned included:

• Flammable atmospheres can occur in vessels and pipework other than the digester itself e.g., pre and post digester.
• Methane is not the only flammable gas generated in the AD process.
• Use of ‘black water’ is acceptable, provided the site operator understands the possible impact of this process
• Pre-digestion pasteurisation reduces pathogenic microorganisms, but does not eradicate all microbiological components/activity
• Management of Change is key – where materials/vessels are repurposed, they must be risk assessed and determined fit for purpose
• Plant process and instrumentation diagrams must be regularly reviewed and kept up to date
• Hot work – working with hot or flammable substances is high-risk and requires a Permit to Work system
• Site operators must genuinely engage in the risk assessment process.
• Site operators must obtain regulatory approval prior to altering the design and operation of the plant, and must maintain permit compliance.

You can find the full article on pages 29-32 of the December 2025 Loss Prevention Bulletin found here.

The EA has also shared with us that they will be reviewing their permit determination process and inspection guidance, making amendments where needed and working with HSE. The EA also plans to publish its corresponding incident report in the near future.