Preliminary investigation of the explosion at the 1875 MW gas fired Teesside power station in which three workmen died suggests that it was caused by an electrical fault in a transformer, probably a short circuit. Suggestions at the time that a gas cylinder may have been involved in the explosion have not been confirmed by events.

Hundreds of workers had been on the site at the time, and all were led to safety. The area surrounding the power station was evacuated but there was no danger off site, the company said. The power station is opposite the former ICI Wilton site, which is still a petro-chemical complex.

The explosion occurred in a transformer room on 8 August Two men were killed outright by the blast, and two others were taken to Middlesbrough General Hospital with severe burns. One of them later died, although the remaining survivor was reported, at the time of going to press, to be in a stable condition .

The combined heat and power station, in Lazenby on Teesside, NE England, is operated by the US multinational company Enron. It was closed immediately after the explosion, with Enron teams being sent in to assess the damage before any decision about a restart was made. There was maintenance work going on when the explosion occurred but it is unclear whether the transformer in question was involved in that work.

The official investigation is being carried out by the Health & Safety Executive, who have sent several inspectors to the scene. The police are also on site, looking to see if there is any evidence to support manslaughter charges against Enron, although at the time a police spokeswoman said that it appeared to have been an industrial accident.

The explosion was the third incident at the plant since it was built eight years ago. Two previous accidents left two employees seriously injured, one partially blind and deaf. On each occasion Enron was fined.

•In an unrelated development Enron president and chief executive Jeff Skilling has decided to end his long association with the company. According to the official statements his reasons are entirely personal, and unconnected with Enron’s operations, which have seen the company’s shares drop to half their peak value of $90 following rapid expansion in 1999-2000, when in common with other aggressive big players Enron anticipated huge growth in tech related sectors. Nonetheless the announcement is a surprise – Skilling had been ceo for only six months, a period that saw the company accused of manipulating California power prices and involved in legal battles in India.

For the time being his duties are being taken over by Kenneth Lay, currently chairman of the company and Skilling’s predecessor as ceo. Mr Skilling will continue to act as a consultant to Enron.