Accidents involving tower cranes seem to have become an all too common occurrence over the past couple of years. Fatal accidents in Battersea last year, Liverpool earlier this year, and the collapse of a crane in Croydon on 2 June have shone a spotlight on the practices of tower crane owners.
According to the Health & Safety Executive (HSE), crane collapses such as these “are still rare” and there has been no significant increase in the number of accidents involving tower cranes. It says: “In six years there have been four fatal incidents where there have been eight fatalities.
“However, any incident is one too many, and because of the nature of tower cranes, when something goes wrong people get badly hurt or killed.”
The HSE cites the ICC RIDDOR database, which lists seven reported accidents involving the collapse of a tower cranes since 2004/05. However, CJ knows of seven accidents involving tower cranes in the past nine months, and has been told by industry bosses that several other incidents have gone unreported. Clearly the official statistics do not tell the full story.
A feature in the 28 February edition of CJ explained the factors contributing to the rise in tower crane accidents: the UK’s tower crane population has grown more than four-fold in the past 10 years, but the pool of competent, experienced and well-trained workers to erect, inspect, maintain and operate them has not grown at the same rate.
Plant consultant Tim Watson says: “It’s stretching the resources of the tower crane owners in finding experienced people.”
With the construction industry booming, tower crane fitters are under the same pressure as everyone else to get things done quickly and move on to the next job.
They work hard, for long hours, often driving many miles on the road every day before and after work. In this environment, the challenge is to ensure that safety is not compromised by short-cuts. With a tower crane, of course, an accident is likely to be more spectacular and cause more damage to life, limb, wallets and construction schedules than any other piece of equipment on site.
Canary Wharf incident
As previously reported, the tower crane industry has made a lot of effort to set its own house in order since the high profile fatal accident in May 2000 at Canary Wharf. A Tower Crane Interest Group (TCIG) has been set up within the Construction Plant-hire Association (CPA), which has published numerous HSE-approved guidance documents and been centrally involved in the development of both new standards and a new training regime, including a course and NVQ for tower crane erection, under the auspices of the Construction Skills Certification Scheme (CPCS).
However, this is not enough, admits Paul Phillips, chairman of the TCIG. “One of the biggest questions that has been raised about the Tower Crane Interest Group is that we’ve produced a lot of paper, but we are not in a position to implement it. It’s down to the companies to implement it,” he says. “You can take a horse to water, but you can’t make it drink if it doesn’t want to.”
Tower crane owners do take safety procedures seriously. Method statements and risk assessments are diligently produced. Training is carried out. The procedures of Select Plant, for example, which owns the country’s largest fleet of tower cranes, are state-of-the-art. It has a 52-page document, The Safe Operation of Cranes, setting out its procedures. It is available on parent company Laing O’Rourke’s website for all to download.
It was Select, however, that was the owner and operator of the crane that collapsed on 2 June in Croydon on the site of Haymills’ Altitude 25 project.
While in previous tower crane accidents the Health & Safety Executive was able to point a finger at systemic failings in maintenance and operations, at Croydon it was pure human error – either collective or individual – and the HSE was swift to publicise the cause of the accident, which was obvious to anyone who studied the widely published photographs of the aftermath.
At the time of the Croydon accident, Select was raising the height of the top-slewing flat-top Terex-Comedil CTT 181 crane using a standard method known as climbing. With this method, a climbing frame designed by the crane manufacturer for a specific crane model or mast width is attached to the outside of the top mast section just below the slew ring.
The top of the frame is then bolted or pinned to the upper section of the crane. The top mast section is then disconnected from the upper, so that the upper and the mast are connected only by the climbing frame. The climbing frame has a series of double-acting hydraulic jacks which rise up and lift the upper above the top mast section by the height of a single mast section.
A new mast section is then introduced into the frame and secured into place in the tower, then the whole process is repeated until the desired height is achieved.
For high cranes, climbing like this eliminates the need for a costly long-reach mobile crane.
Care is required because the climbing frame is not designed to withstand the same lateral forces as the mast. Therefore, when the top of the climbing frame is attached to the underside of the slew ring, the crane has to be in balance. “Most manuals will tell you the radius that the trolley has to be at with a balance weight on the hook – usually a mast section,” explains Tim Watson. “There is a reasonable margin of error, but not a massive one,” he adds.
There are risks involved, but it is not an especially difficult operation, says Phillips. Watson agrees: “They climb cranes all the time in continental Europe and seldom have problems.”
Select got this climbing operation wrong. As the HSE has confirmed, the erection crew failed to connect the top of the climbing frame to the crane upper, so that when the jacking began the upper was simply balancing on the frame with no physical connection, it over-balanced and fell backwards off the frame. That it came to rest on the roof of the neighbouring Croydon Park Hotel meant that the crane operator, whom the fire brigade had to rescue from the cab, was the only person injured.
The key question is how could the erection crew have missed out such a basic step in the procedure. “With Select, you just can’t believe it,” says the boss of a rival crane company. “It has very good safety systems. It does all the right things that you are meant to, but still there was an accident. Procedures and systems are not enough.
“You need people thinking on their feet. Forgot to pin it? How the hell can you forget to do that?”
Questions will doubtless be asked as to whether the Croydon crew had received adequate training on the workings of the specific climbing frame that was being used, as they are supposed to. Laing O’Rourke, Select’s owner, maintains that the Croydon crew was “adequately trained” and had “gained on-site experience before taking part in climbing operations”.
Although such details as connection designs may vary between different crane manufacturers, the basic operational principles are consistent across all makes. “All climbing frames are different in detail and very similar in principle,” says Watson.
In other words, whatever the make, you still have to connect the frame to the upper, so it seems hard to attribute any possible lack of model-specific training as a cause here.
The over-arching question for the industry is how to eliminate the risk of someone, somewhere, having a senior moment. Everyone, in any walk of life, is prone to forgetting something, dropping something or just making a simple mistake.
It is an inevitability of life. With tower crane erection, however, the consequences can be catastrophic. Such risks are minimised by proper planning, procedures, training and site supervision, but can never be totally eliminated.
So what advice is there for contractors who may be concerned about the recent performance of the tower crane industry?
The HSE says: “Our advice to contractors is simple. They should make sure that the cranes they use are suitable for the specific site conditions, are subject to regular maintenance and thorough examination in accordance with the law, and that the crane driver is suitably trained and familiar with the crane which is to be used.
“They should make sure that all lifting operations are properly planned by a competent person and appropriately supervised. Cranes can be erected and operated safely provided they are properly erected according to the manufacturer’s instructions and by trained staff.”
Paul Phillips has an additional suggestion: if a contractor has concerns about using external climbing frames for tower cranes on a high rise building, they could consider designing the project around a crane inside the core of the building.
“If you’ve got a choice, internal climbing is safer,” he says. “You also save on mast sections [since the whole crane is jacked on to the floors of the building as they are built].
“The downside is that you need a large mobile crane or a special derrick system to remove it.”