Contractor fined over tower crane accident

A recent prosecution in Liverpool offers a timely reminder of the actual and potential consequences that can follow the collapse of tower cranes. The prosecution ended with the principal contractor for a multimillion pound development being fined £280,000 for failures that caused a crane to overturn.

As the controversy over the HSE's proposed repeal of the conventional tower cranes register continues (see box 1), a recent prosecution in Liverpool ended with the principal contractor for a multimillion pound development being fined £280,000 for failures that caused a crane to overturn, paralysing its driver from the waist down and causing major damage to a nearby apartment block. The HSE's investigating inspector said it was "no exaggeration to say it was only by pure chance that this catastrophic event did not result in multiple fatalities and significantly more damage to property". The structural engineering firm responsible for the design of the crane's foundations was fined a nominal £1,000; had it not been in liquidation, the judge said he would have imposed a fine of £400,000.

The HSE believes the main lessons of the collapse for the construction industry are:

• designers of tower crane foundations must ensure they are familiar with industry-accepted guidance (PDF format, 1.37MB) (on the CIRIA website) and follow it, unless they have very well thought-out reasons for not doing so;
• the role of the principal contractor is crucial in managing the design process; and
• principal contractors and designers must ensure that robust systems for design checking are put into practice at all times.

Tower crane collapse

The incident occurred on 6 July 2009 during the construction of a new eight-storey hotel and seven apartment blocks at Kings Dock Mill in Liverpool. The foundation of the 79-metre-high tower crane - a Luffing slewing jib - which had replaced a previous crane on 16 April, was unable to support the forces generated by the crane and, as a result, the crane overturned and fell across a road before coming to rest on a block of 64 apartments at nearby Chandlers Wharf. Eight counterweights on the crane, which together weighed 56 tonnes, broke free and crashed through the roof and six floors of the Chandlers Wharf building.

The crane's driver, Iain Gillham, travelled through the air in his cab before falling out of it five or six metres onto the roof of the Chandlers Wharf building and then through the hole created by the counterweights to street level. He suffered a brain haemorrhage, fractured skull, broken right shoulder, broken ribs, crush injuries to his left side, and major spinal injuries that resulted in his paralysis.

The Chandlers Wharf residents were unhurt but had to be evacuated; some were rescued from their balconies. The block was so badly damaged that its residents were unable to return to their homes for almost two years.

Foundation was inadequate

The HSE's investigating inspector, Warren Pennington, told Health and Safety Bulletin (HSB) that the site's principal contractor, Bowmer & Kirkland, found during the construction of the foundation that the crane's four feet were unable to sit on top of the four concrete foundation piles. The problem was that the 32mm essential steel reinforcement bars ("Dwyidags") that ran through the centre of the piles were protruding at the point where the design specified the feet were to be placed. The Dwyidags were the main structural component for withstanding the forces arising from the tension. In the design, each of the four feet was supposed to be fixed within the pile cap, which is a combination of 40 tonnes of concrete and bars, connected with the four piles beneath it.

Bowmer & Kirkland telephoned Bingham Davis, the structural engineering company that had designed the pile cap. As a result of the conversation, the companies agreed - although Bingham Davis disputed this in court - to cut away the Dwyidags from the four concrete foundation piles, so that the crane's feet could sit flat on top of the piles. Bowmer & Kirkland then drilled in four or five steel dowels to fix each pile to the cap, as specified in the amended design, but the dowels could only withstand a reduced force and together with the cut-away Dwyidags resulted in the foundation being too weak to support the crane. To compound matters, Bowmer & Kirkland did not insert the dowels to the 400mm depth that the amended design required, thereby further weakening the foundation, although this was not as significant a failure as the cutting of the Dwyidags. Summing up, Judge Gilmore said he was satisfied that it was these actions that led to the foundation being overloaded and the crane collapsing. He also criticised what he called "the casual nature of the discussion" between the two companies.

Circumstances leading to collapse

Pennington described the circumstances leading to the collapse as "a mess". Bingham Davis's employees had no previous experience of designing the type of crane foundation used at Kings Dock Mill; Bowmer & Kirkland's employees at Kings Dock Mill had no experience of building one. "Both parties," he said, "made disastrous errors that were entirely preventable," while neither "did enough to check what the result would be of cutting away this essential steel reinforcement and replacing such with dowels."

Furthermore, following the phone call with Bingham Davis, Bowmer & Kirkland's site manager wrote the instruction for the amended design down and gave it to the workers. Crucially, said Pennington, he did not send the amended design back to Bingham Davis for checking and signing off, which he should have done routinely. Both companies, he added, had systems that should have been more than adequate to prevent the collapse; the problem was that neither followed their systems for changing the design.

There was also a third component to the case, Pennington told HSB. Although Bingham Davis was responsible for the design of the pile cap, another company, Van Elle, was responsible for the design of the piles. The HSE alleged that the tensile capacity of the foundation that Bingham Davis calculated and gave to Van Elle underestimated what was needed by a factor of six. This, said Pennington, meant that the crane would have been likely to collapse irrespective of the cutting. Bingham Davis, he said, made the "original error" in that it "failed to spot a basic mistake in its calculations for the loadings imposed by the crane. This created a material risk which had the potential to have led to a crane foundation being constructed that was not strong enough to hold the crane up." The judge, however, said he was "not sure that the crane was doomed from the beginning".

Contractor fined £280,000

Following a trial that started at Liverpool Crown Court on 16 April, both companies were found guilty on 9 May of breaches of the HSW Act. Judge Gilmore fined:

• Bowmer & Kirkland £280,000 for failing to ensure the safety of its employees (s.2(1)) and for exposing people other than its employees to risks to their safety from its undertaking (s.3(1)). The judge did not split the fine between the offences. He subsequently ordered the company to pay £195,000 towards the HSE's costs of £400,000. In the year to 31 August 2011, the company made an operating profit of £44.33 million on a turnover of £708.27 million, results that were 32% and 6% higher than those of the previous year; and
• Bingham Davis £1,000 for a breach of s.3(1). The company, which went into voluntary liquidation after the crane collapse, presented figures to the court showing that it was around £1 million in arrears. The judge said that but for the liquidation, he would have imposed a fine of £400,000; the company escaped paying half of the HSE's costs for similar reasons.

In mitigation, the judge said there was neither a death nor any indication of cost cutting and that Bowmer & Kirkland had cooperated "to a high level" with the HSE and had an otherwise good safety record. (In fact, Bowmer & Kirkland has previously been fined twice for health and safety at work failures - £15,000 in 2008 and £9,000 in 1999. It also received seven prohibition notices and two improvement notices between 2001 and 2011. None of the prosecutions or notices was related to cranes. Bingham Davis had not faced any previous enforcement action.)