BP Chemicals has been fined £30,000 at Hull Magistrates Court for two offences after pleading guilty to a leak of gas containing carbon monoxide from its plant.
The chemical company was also ordered to pay costs of £5,220 to the Environment Agency, which brought the case.
BP Chemicals' site at Saltend is part of a large chemical complex in Hull, where it manufactures approximately 750,000 tonnes of organic chemicals each year. All activities on the site are regulated by an environmental permit issued by the Environment Agency.
The court heard that a raw product called synthesis gas or 'syngas' is produced at the site, which is made up of carbon monoxide, hydrogen, carbon dioxide, methane and water. Carbon monoxide, which is classed as toxic, together with methane and hydrogen have the potential to be highly flammable.
Craig Burman, prosecuting for the Environment Agency, told the court how between 10 November, 2009 and 11 December 2009, a total of 572 tonnes of syngas was released into the atmosphere. This consisted of 324 tonnes of carbon monoxide, 175 tonnes of carbon dioxide, eight tonnes of methane and 65 tonnes of hydrogen.
The release of syngas happened due to a valve failure, which cause vibration and led to the fracture of a metal tube in one of the site's heat exchangers. This caused syngas to enter a cooling water line and be released into the atmosphere from one of the plant's cooling towers. There were no alarms to detect this release.
The pH analysers fitted to the cooling water lines were indicating low pH levels on the cooling water return line from 14 November 2009.
Between 17 November and 6 December 2009, technicians carried out a series of tests but were unable to detect the leak of syngas.
On 7 December, 2009 it was discovered that technicians had been taking samples from the cooling water supply line rather than the cooling water return line. The leak was detected when a technician attempted to take a sample from the cooling water return line, and his personal carbon monoxide alarm was activated.
The Environment Agency was informed of the leak the following day, and that part of the plant was shut down for two weeks whilst repairs were done and an internal investigation launched.
Mr Burman told the court that had staff sampled the return line earlier, the syngas would have been found sooner. It was calculated that 400kg per hour of syngas was being released into the cooling water return line, which was then being released into the atmosphere from one of the cooling towers.
BP Chemicals Ltd accepted that a procedure was not in place for sampling from the cooling water return line, and there was no procedure in place to identify a possible leak into the return line.
Although the valve that failed was designed to fail in the open position, there was no system in place to monitor it. No vibration modelling had been carried out on the heat exchanger. BP Chemicals Ltd also accepted that information was not passed up the chain of command to more senior management.
Mr Burman explained to the court that there had also been two previous unauthorised releases of syngas at the plant in December 2004 to January 2005, and from April to July 2005. He also said that the possibility of damage caused by vibration was foreseeable and was known to the defendant.
In mitigation, BP Chemcials Ltd said this was a single incident and there was no breach of air quality standard for carbon monoxide. They said no harm was caused to employees or members of the public, and that environmental impact was minimal. They had a high level cooperation with the Environment Agency throughout the investigation, and pleaded guilty at the earliest opportunity.
BP Chemicals Ltd has also made changes to the plant to prevent this from happening again.
The court noted that there was no harm to residents and employees, and no environmental harm, but noted that it was a 'lengthy' period before the leak was discovered.
Speaking after the case, Darren Leng, regulatory officer at the Environment Agency said: 'Whilst on this occasion there was no impact on the environment or human health, we take breaches of environmental permits very seriously, and always take action where appropriate.'