This was an HSE declared major incident.
A company transported waste water/sludge, using a tanker lorry, from food factories and abattoirs to various farms for spreading on agricultural land. This involved transferring the waste from the tanker into a holding tank (at the side of the field) from which it was pumped to a tractor for spreading on the agricultural site.
On occasions a thick sludge built up in the bottom of the holding tank, requiring an employee to climb onto the top of the tank and use a high-pressure hose to dislodge and dilute the sludge. On the occasion in question the person undertaking the task fell into the tank through an open manway. As the tank contained decomposing waste the atmosphere inside the tank was incapable of supporting life due to carbon dioxide levels being raised and oxygen levels lowered (e.g. aerobic fermentation by bacteria within the waste).
When the operative fell into the tank he was overcome by the atmosphere and became unconscious. He fell into the liquid at the bottom of the tank and drowned. Two men who attempted a rescue also suffered the same fate. A fourth man also tried a rescue but managed to get out.
The company and their directors were successfully prosecuted. There were no measures to prevent access to the tanks, training and risks assessments were poor and the judge commented on the reckless disregard for health and safety.
The company was fined £72,500 with £50,000 costs and the Directors fined £10,000 each.
There was a high level of local and national media interest.