BLOWOUT of a compressed air section of a Docklands Light Railway (DLR) tunnel during construction was the result of an 'elementary error, indeed a blunder' by contractor Nishimatsu, a crown court judge said on Monday.
Nishimatsu had pleaded guilty to the charge of failing to ensure the safety of people it does not employ, following the catastrophic tunnel explosion.
The judge fined Nishimatsu £700,000 for breaching the Health & Safety at Work Act as well as ordering the contractor to pay prosecution and defence costs. This left the contractor facing a total bill of £1M.
The blowout which occurred at 4.45am on 23 February 1998, created a 22m wide, 7m deep crater in the grounds of George Green school and showered nearby buildings with debris (NCE 26 February 1998).
'Overlooking the risk of blowout due to internal pressure build-up in the tunnel was an elementary error, indeed a blunder, ' Judge Ian Karston told Middlesex Guildhall Crown Court.
'The risk was obvious and well within the competence of any civil engineer, ' he said.
The fine was the third highest ever for a construction accident, even though no-one was hurt.
The court heard that 'serious and gross failures' on the part of Nishimatsu led to the explosion.
The company was working on a design and build contract to construct two tunnels, which would take the DLR from Mudchute station north of the Thames to Cutty Sark station south of the river.
The project was a privately financed design build finance and operate (DBFO) project funded by a consortium called CGL Rail, of which Nishimatsu was a member.
During the hearing the court heard that in February 1998 Nishimatsu was carrying out trials to pressurise one of the tunnels using compressed air.
This pressure was needed to prevent water seeping into the tunnel during construction of a cross passage.
Prosecuting barrister Julian Lambert QC told the court that calculations carried out for the contractor showed that the pressure exerted by groundwater on the tunnel lining at its deepest point was 2.9 bar.
Contractors were aiming to build up to a resistant air pressure of 3 bar before digging.
Steel bulkheads were used to seal the tunnel at two locations.
The first was placed 60m from the tunnel entrance and the second was placed 60m past the cross passage location.
At 4.45 am on 23 February the pressure had reached 2.1bar when the tunnel exploded close to the bulkhead nearest the tunnel's northern portal.
At this point there was not enough overburden to resist internal forces exerted by the compressed air and this led to a rapid escape of pressure.
'The Health & Safety Executive's investigation failed to reveal that any calculations had been carried out for the overburden pressure along the tunnel, ' Lambert told the court.
'Nishimatsu failed to ensure that the matter of overburden was investigated, ' he said.
Nishimatsu's defence had sought to shift some of the blame for the blowout onto its tunnel designer WS Atkins Consultants (see box).
Construction's biggest fines
£1.2M against Balfour Beatty for the 1994 Heathrow Express collapse.
£750,000 against Swedish contractor FEAB after the 1995 Ramsgate walkway collapse £700,000 against Nishimatsu this week.
£500,000 against Geoconsult for the Heathrow Express collapse.
£500,000 against Balfour Beatty Rail Maintenance for the 1997 derailment at Rivenhall, Essex £500,000 against Kvaerner Cleveland Bridge for the 2001 Avonmouth gantry collapse.
Average fine in construction in 2002: £5,698
Judge refuses late fine payment
Judge Karston turned down a request from Nishimatsu to delay paying its fine.
He said that a £700,000 fine should be high enough to bring home to Nishimatsu shareholders the importance of a company maintaining a safe environment.
But for the defence, Jonathan Caplin QC asked that the defendants be given three months to pay the fine rather than the usual 28 days.
The judge refused, saying that the delay could take the contractor into a new financial year. He said this could give the firm a choice about the financial year in which the fine would appear in its accounts.
Judge Karston said this would not fit with the objective of making shareholders feel the impact of the fine.
In a statement after sentencing on Monday Nishimatsu deputy general manager Peter Fisher said that the company was surprised at the level of the fine and was reviewing its legal options.
The judge ordered Nishimatsu to pay its fine and the costs by Monday 15 March.
Consultant faces court case
During the hearing it emerged that Nishimatsu is mounting a civil case against WS Atkins Consultants over its role in the blow out.
The court heard that the contractor was claiming that WS Atkins should have warned it about the risk of a blow out while compressed air was in use. That case is due to be heard in April.
During last week's trial Nishimatsu attempted to share some of the blame for the blowout with consultant WS Atkins.
Defence lawyers for Nishimatsu, accused WS Atkins, which now trades as Atkins, of failing to carry out its obligations as tunnel designer.
'Nishimatsu assumed that all necessary calculations relevant to the integrity of the tunnel lining had been carried out by WS Atkins, ' said Caplin.
But during sentencing this week the judge told the court that it was clear that Nishimatsu had failed to ask WS Atkins to carry out the relevant calculations.
He said there was no evidence to support Nishimatsu's claim that it had assumed WS Atkins had done the calculations.
WS Atkins refused to comment on either case to NCE.
Missing specification added to standard
The Docklands Light Railway tunnel blowout led to the rewriting of the British Safety standard for tunnelling.
BS6164 is the code of practice for safety in tunnelling in the construction industry.
Following the 1998 blowout the Health & Safety Executive noticed that the need to account for overburden during compressed air working was not specifically mentioned in the standard.
Section 11 of the code, which relates to the use of compressed air, now has specific clauses relating to ground strength.
Clause 11.1.3 now states that 'the ability of the ground to sustain air pressure from within a tunnel can limit the pressure used. This should be determined by an assessment of the overburden at all parts of the tunnel at all stages of construction.'