Safety: Chemical Accident Investigation

Article by Keith Plumb CEng FIChemE

The UK needs its own ‘Chemical Safety Board’, says Keith Plumb

Cheshire Fire & Rescue Service
2015 explosion at Wood Treatment, Bosley Mill

I AM concerned that in the UK, the Health and Safety Executive’s (HSE’s) drive to prosecute companies and individuals when they breach health and safety regulations is preventing important technical information and lessons learnt from being published.

For example, on 17 July 2015 there was large explosion at Wood Treatment, Bosley Mill, Congleton that completely destroyed the factory and killed four workers. Almost certainly this would have been caused by a dust explosion, but I have been unable to find any official report on the cause of the explosion.

The case did go to court and four possible scenarios were highlighted during the court case, but in the end manslaughter charges were dropped. However, the managing director pleaded guilty to health and safety offences and was fined £12,000 (US$14,500) and banned from being a company director. The firm was fined £75,000. The court case was concluded on 29 April 2021.

Similarly, on 3 December 2020 there was a large explosion in a silo at Wessex Water’s waste treatment plant in Avonmouth. The ongoing investigation is being led by the Avon and Somerset Police with the help of HSE. So far there has been no word on what caused it.

I believe it’s high time the UK had a separate process industry accidents investigation unit that gets safety lessons to the engineers who need them before more mistakes are repeated.

Silo explosion at Avonmouth near Bristol in December 2020

Leading by example

In my opinion, the US chemicals industry is already ahead of us on this, as is the UK’s rail industry, for example. The US Chemical Safety Board has the following stated mission:

“The US Chemical Safety Board (CSB) is an independent, nonregulatory federal agency that investigates the root causes of major chemical incidents. Our mission is to drive chemical safety change through independent investigations to protect people and the environment”

Looking at comparable incidents to those mentioned earlier, there was a dust explosion at West Pharmaceutical Services, Kinston, North Carolina, US on 29 January 2003. The CSB final report on the incident was released the following year on 23 September 2004. This is a very detailed report analysing the explosion and the potential causes. The lessons learnt from this report are hugely significant to any process safety engineers working in this field.
Similarly, the CSB report for a dust explosion at Imperial Sugar, Port Wentworth, Georgia, US on 7 February 2008 was released on 24 September 2009.

This suggests to me that having an emphasis on progressing prosecutions is getting in the way of finding the technical details of what caused an explosion or other major incident – and I am not the only one with this opinion. Chemical engineer David Slater (former Chief Inspector of Pollution and Director of the Environment Agency) wrote the following in his white paper Why don’t we learn from disasters?

Having an emphasis on progressing prosecutions is getting in the way of finding the technical details of what caused major incidents

“There are two separate and conflicting drivers behind most investigations of accidents: the need for understanding what happened, and the need for justice […] The second driver, the need to assign blame, often leads to the investigations stopping, once a blameable (‘root’) cause has been agreed.”

In October 2005 the UK rail industry came to the same conclusion after two rail crashes on the approaches to Paddington Station had pushed the industry to change its approach, and the Rail Accident Investigation Branch was set up with the stated purpose of:

“The Rail Accident Investigation Branch (RAIB) independently investigates accidents to improve railway safety, and inform the industry and the public.”

The regulatory and criminal aspects are still covered by HM Inspector of Railways and the Transport Police, but RAIB has a similar record to the CSB in rapidly publishing detailed technical reports. For example, the derailment of a passenger train at Carmont that occurred on 12 August 2020 is covered by a report published in March 2022.

If the rail industry can do this (air and maritime accidents are treated similarly) then why can’t the chemical industry? There would still be a role for HSE but a Chemical Accident Investigation Branch with the purpose of investigating accidents to improve process safety, and to inform the industry and public, would in my opinion be a major step forward.

With our strong focus on major hazards, IChemE should take a lead role in promoting this change by initiating discussion with the Department for Work and Pensions via the Royal Academy of Engineering – the Government’s main contact body for engineering matters.


1. The Hon Mrs Justice Day DBE, Regina-and-(1) Wood Treatment Ltd (2) George Boden Sentencing Remarks, T20197350, Chester Crown Court,
2. US Chemical Safety and Hazard Investigation Board, Investigation Report, Dust Explosion, West Pharmaceutical, Services, Inc, Report No. 2003-07-I-NC, September 2004,
3. US Chemical Safety and Hazard Investigation Board, Investigation Report, Dust Explosion, Imperial Sugar Company, Report No.2008-05-I-GA, September 2009,
4. David Slater, Why don’t we learn from disasters?, 2020,

Article by Keith Plumb CEng FIChemE

Process, Safety and Equipment Consultant at Integral Pharma Services

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