The incident occurred on 11 March 1997 when an 8,000-litre batch of dimethyl acetamide was being heated prior to distillation. A few weeks earlier Croda had fitted a new, more efficient heat exchanger to the still. Because this permitted rapid heating, some 80kg of ethylamine - a volatile contaminant present in the mixture - was driven off at such a rate that it overwhelmed the plant's wet scrubber.
The chemical is a lung irritant with a strong ammonia-like smell. Croda was alerted to the release by a telephone call from a local resident and immediately stopped the process.
However, one member of the public was hospitalised overnight after suffering nausea and disorientation. Several other people were affected, including one woman who a week later coughed up blood-stained mucus - a symptom consistent with acute short-term exposure to ethylamine.
The Environment Agency charged the company with breach of its integrated pollution control authorisation, contrary to section 6(1) of the Environmental Protection Act 1990. The Agency says that Croda had produced no written hazard assessment of the modification to the plant, and that procedures for controlling the rate of heating were inadequate.
Although Croda pleaded guilty, local magistrates twice referred the case to the Crown Court because they considered that the maximum £20,000 fine which they were permitted to impose was inadequate.
The case was heard at Leeds Crown Court on 20 February - but the judge imposed a fine of only £5,000. Croda was also ordered to pay the Agency's costs of £2,713.
Howard Leberman, the Agency's inspector, said that "modifications to the plant and a review of procedures have now been completed which should ensure that such an incident does not occur again." Overall, he said, the Agency is content with Croda's progress in reducing emissions - notably a reduction in annual releases of volatile organic compounds from over 700 tonnes to 25 tonnes over the last year.