A CATALOGUE of design and management errors combined with poor workmanship and quality control were at the root of the catastrophic tunnel collapse at Heathrow Airport in 1994.
So says the Health & Safety Executive in its final report on the 1994 Heathrow Express collapse.
The report, which was the result of years of investigation by the HSE's specialist team, was published after completion of the legal proceedings and was largely guided by the outcome of the case (Ground Engineering March 1999).
Investigators found the incident exhibited 'all the hallmarks of an organisational accident'.
'The collapses could have been prevented but a cultural mindset focused attention on the apparent economies and the need for production rather than the particular risks, ' the report says.
'Warnings of the approaching collapse were present from an early stage in construction but these were not recognised.'
Errors were made, it says, 'leading to poor design and planning, a lack of quality during construction, a lack of engineering control and most importantly, a lack of safety management.'
The tunnels collapsed in the early hours of Friday 21 October 1994 and continued to fail over a number of days.The resulting crater and the measures taken to shore up the tunnels brought chaos to the heart of Heathrow Airport.
No one was killed or injured in the accident, but HSE considers it 'one of the worst civil engineering disasters of the last quarter century'.
Recovery of the situation took nearly two years and cost £150M - three times the cost of the original contract. Other projects in the UK using sprayed concrete tunnelling methods, including the Jubilee Line Extension and the Heathrow Airport baggage tunnel, were voluntarily suspended during the investigations.
Prosecutions resulted in contractor Balfour Beatty and its tunnel designer Geoconsult being fined a total of £1.7M - a record at the time for offences under health and safety legislation.
'Such accidents must be prevented through effective risk management. The industry cannot simply rely on good fortune, ' says the report. 'Risk assessment should be a fundamental step in the procedures adopted by all parties: it is inappropriate wholly to leave the control of risk to contractors.'
The report highlights the risk of safety-dependent activities being influenced by contractual relationships.'Cases in point may be new forms of contract where roles are poorly understood and new technologies where people variously rely on others to understand, communicate and control the risks.'
To overcome this, the report says, 'those involved in projects with the potential for major accidents should ensure that they have in place the culture, commitment, competence and health and safety management systems to secure the effective control of risk and the safe conclusion of the work.'
The HSE says the direct cause of the tunnel collapse was a chain of events. This included a myriad of unchecked substandard construction over a period of three months, grout jacking that damaged the tunnel and inadequate repairs two months before the collapse.
The collapse of NATM tunnels at Heathrow Airport, published by HSE Books, tel: 01787 881165; www.hse.gov.uk