Taunton magistrates heard the developer failed to advise ground workers of the presence of an underground gas main.
An excavator struck and ruptured the pipework at a site in Norton Fitzwarren, near Taunton, on 11 October 2012, because the driver was completely unaware it was beneath him as he dug a trench.
It caused the closure of the nearby main railway line to the South West for emergency repairs, and landed BDW Trading Ltd, trading as Barratt Homes, in court.
An HSE investigation found that BDW Trading Ltd had failed to properly plan the work.
The company had neglected to contact the utility owners to obtain up-to-date plans of the site.
As a result safe digging techniques were not being used because no-one on site had reason to believe they were working anywhere near a gas pipe.
The court heard how a consortium of house builders was engaged in a long-term development project at the site, and that several different subcontractors had worked there over a number of years prior to work stopping in 2008 due to the recession.
Two gas mains operated by separate supply companies run across the site and in 2009 one of these was renewed and re-routed.
When building work recommenced in 2012, BDW Trading Ltd supplied its groundwork contractors with site maps that did not cover the entire site, and that did not show the new route of the gas main.
BDW Trading Ltd, of Bardon Hill, Leicestershire was fined £16,000 and ordered to pay £25,000 in costs after pleading guilty to breaching CDM Regulations
Speaking after the hearing, HSE Inspector Sue Adsett said: “More than 11,000 cubic metres of gas escaped as a result of this incident, one of the largest releases of gas in the South West in recent years.
“It was sheer luck no-one was injured. As it was, the incident caused huge disruption to rail services and passengers.
“It could so easily have been prevented if BDW Trading Ltd had obtained up-to-date plans from the gas supplier after pipes had been relocated on their site in 2009, or upon restarting work at the site in 2012.
“BDW Trading Ltd’s fundamental error was to start work in the area without adequate gas utility drawings.
“House builders should be especially careful when they start working on a site where construction work has stopped and started because vital information may have been lost.”