The US Chemical Safety Board (CSB) is continuing its detailed investigations into the ammonium nitrate explosion at West Fertilizer in Texas, which left 15 people dead, around 200 injured, and widespread destruction in the small town of West, located between Dallas and Waco.
Initial indications point to a warehouse fire that lasted for around 30 minutes before causing detonation of stored ammonium nitrate, resulting in an explosion equivalent to a magnitude 2.1 earthquake.
According to the Institution of Chemical Engineers (IChemE) and its incoming President, Judith Hackitt CBE, it is clear that lessons are still not being learned from previous incidents and the process industries need to do more.
“We must nurture and preserve the vital lessons that have been learned through success and failure in the process industries,” said Hackitt. “We must ensure that we have the mechanisms to build upon, to share and to actively transfer our knowledge to the best advantage of our profession.”
The incident in April at the West plant near Waco in Texas illustrates her point well. Although the cause of the explosion is still being investigated, one chemical – fertiliser and explosive called ammonium nitrate – known to be stored on the site has been linked to other major incidents over the past 90 years.
We must nurture and preserve the vital lessons that have been learned through success and failure in the process industries
In 1921, at Oppau in Germany, 430 people were killed and 2,000 injured. In 1947, at Texas City, US the freighter the SS Grandcamp exploded with 5,000 people injured and almost 600 dead. In 2001, a huge explosion ripped through the Azote de France fertiliser plant on the outskirts of Toulouse, France, killing 30 and injuring a further 2,000 people.
According to the US Chemical Safety Board (CSB), it is examining many issues surrounding the explosion, including the storage and handling of ammonium nitrate there. Most significantly, perhaps, the investigation will examine the adequacy of national standards, industry practices, and regulations for the safe storage and handling of ammonium nitrate.
The UK’s Control of Major Accident Hazard regulations relating to the presence of hazardous chemicals such as ammonium nitrate derive largely from the EU Seveso directives. These require measures such as notification of the HSE, emergency planning, and preparation of safety reports depending on the quantities of material stored at an installation.
In addition to regulation, there is a UK industry scheme called the Fertiliser Industry Assurance Scheme. This is designed to provide safety, security and traceability through from primary manufacture to the farm gate, including manufacturers, warehousing and distribution participants.
With regards to local planning rules, an industry watcher commented: “HSE’s approach to evaluating risk from chemical facilities is well-developed and would take into account residential or public buildings close to a proposed development.”
“However, as at Buncefield, many of UKs facilities pre-date current regulations, and in circumstances where the risk could be high, there is a discussion between the operator, HSE and local authority as to the best way forward.”
For Graeme Ellis of ABB Consulting, however, the explosion at the Texas fertiliser plant is another reminder of how the process sector fails to adequately control major accident hazards.
The accident, notes Ellis, occurred a day after publication of an investigation report from the US Chemical Safety Board on the Chevron Richmond Refinery fire in August 2012, showing that a high temperature carbon steel pipe had ruptured due to ‘sulphidation’ corrosion.
The CSB found that this mechanism is well known in the refining industry, and pointed to a failure to learn from previous incidents and install ‘inherently safer’ piping materials on this duty that would have avoided this type of corrosion.
“It would be tempting to conclude that the Waco accident was unforeseeable and that a number of unfortunate factors had conspired to cause the explosion,” said Ellis. “These types of events are thankfully rare, but companies handling ammonium nitrate should be aware of similar explosions, including one at a fertiliser plant in Toulouse France in September 2001.
“This event was thought to have involved a 300-tonne store of contaminated ‘reject’ material, that exploded killing 29, injuring around 2,500, and shattering windows up to 5 km away. In another accident described as the ‘worst industrial accident in US history’, a ship being loaded with 2,300 tonnes of Ammonium Nitrate in the Port of Texas caught fire and exploded, killing around 576 people and flattening 1,000 buildings.”
Although it is too early to speculate on the causes of the Waco explosion, Ellis notes that a common finding on similar accidents is a failure to carry out adequate PHA – a key aspect of an effective process safety management system.
“The essential aspects of PHA are to identify credible hazards based on the properties of the substances being processed, select suitable control measures to reduce risks to a tolerable level, and then manage these control measures to achieve reliability throughout the lifetime of the facility,” said an ABB expert.
In the UK, the HSE publishes a code of practice for the safe storage and handling of ammonium nitrate, reference INDG 230, and readily available on its website. This classifies AN as an explosive that can detonate when heated, with the risk increased if the material is contaminated.
The HSE guidelines give a number of requirements for safe storage, including locating AN either outdoors or within buildings that ‘will not burn’, and limiting the size of storage stacks to control the scale of an explosion.
“Companies operating ‘major accident hazard’ facilities should critically review the competence of the teams carrying out PHA’s, where they are using established techniques such as HAZID and HAZOP. These studies can appear fairly mechanistic in nature and can place a great demand on scarce skilled and experienced resources,” said Ellis.
“A serious management shortcoming is to assume that less experienced teams will be capable of producing adequate results and conclusions,” he added. “The team leader has a critical role and needs to be highly competent in all aspects of process safety, and capable of steering the team based on an in-depth understanding of the causes of rare ‘process industry incidents’.
“If the process industry is to achieve a step change improvement and avoid the human toll and negative image it needs to take on board [the lessons from] accidents such as the explosion at [West].”
Robin Turney, chairman of IChemE’s Loss Prevention Panel, believes that to reduce accidents all parts of process safety, including the technical understanding, the human factors and the importance of a safety culture, need to be linked together.
“The more people who have a good understanding of process safety and what can happen when things go wrong, the better,” he said.
“We’ve always recognised its importance, and perhaps those companies who’ve had the major incidents haven’t recognised just how important. It’s about bringing all the elements together”.
UK safety regime - dealing with ammonium nitrate
According to a Health and Safety Executive (HSE) spokesperson, there are two sites manufacturing ammonium nitrate in the UK - one is near Chester and the other in the North East - both operated by Grow How. There are also, she pointed out, other industrial plants in the UK that store ammonium nitrate and similar materials.
“Such plants are subject to a strong legislative regime designed to help prevent major accidents involving dangerous substances, and limit the consequences should they occur. The following background sets out the legal framework and how it works,” said the HSE representative.
Under the UK’s framework for controls on hazardous substances, the legal duty for the safe operation of sites storing hazardous substances, including ammonia based compounds, rests with the site operator.
They have to control the risks to people who live and work nearby, as well as to site workers and to the environment. The storage of hazardous substances, including ammonia based compounds, is subject to hazardous substances consents issued by local authorities, which control the amounts that can be stored by operators.
Health and safety legislation is applied by the HSE, which deals with the safe operation of sites. HSE is jointly, with the Environment Agency and Scottish Environment Protection Agency, the Competent Authority for The Control of Major Accident Hazards Regulations 1999 (COMAH).
Local authorities, meanwhile, place controls on development around sites where hazardous substances are present and are required to consult HSE before granting HSCs. The Local Authority also decides on planning applications, having weighed up all material considerations including safety advice from HSE.
The National Planning Policy Framework makes it clear that planning policies should be based on up-to-date information on the location of major hazards and on the mitigation of the consequences of major accidents and that local planning authorities should consult the appropriate bodies when planning, or determining applications, for development around major hazards.