Morgan Sindall and Leeds-based Northern Gas Networks Operations have been found to have “neglected basic safety measures”, leading to a gas blaze that saw six homes evacuated.
The closure of a major road was also forced, while gas supplies were cut off, Leeds Crown Court heard yesterday.
A major construction project on the Ring Road at Beeston was underway, with a new section of gas mains installed.
However, the court heard that numerous safety failings by both companies had led to welding work on a gas main sparking the fire, which sparked a fire reaching 20-feet high in September 2010.
Three workers fled to escape, with fire crews using water jets to protect nearby properties.
The fire brigade was on the scene for more than ten hours, and the ring road was closed for two days.
The Health and Safety Executive investigated the incident and prosecuted Northern Gas Networks Operations, known as United Utilities at the time, and Morgan Sindall (Infrastructure) for safety breaches.
The HSE found two of the firms’ sub-contractors had only been competent in specific parts of the job, with neither fully understanding the overall work.
NGNO and MSI were found to have failed to effectively plan the work or provide appropriate safety controls.
They pleaded guilty to a single offence under the Health and Safety at Work Act 1974.
NGNO was fined £35,000 and ordered to pay £8,453, while Morgan Sindall (Infrastructure) was hit with a £50,000 fine and £12,900 in costs.
After sentencing, HSE inspector Ian Redshaw said: “Someone could have been killed or badly injured in this incident. Thankfully no one was hurt, but this was a severe fire that was a danger to workers and local people.
“There were numerous failings by both companies in the planning, organisation and execution of the work – most importantly the failure to consider and control the risks associated with welding near live gas mains.
“When undertaking high hazard activities such as this, it is essential that the proper steps are taken to ensure that risks are fully considered and then controlled.
“This type of activity is regularly undertaken in the gas industry and all the safety practices are well established and common knowledge in the industry. Thankfully incidents are rare, but if they do occur the consequences can be devastating.”