20.02.2003

HSE warns on hazardous tower cranes

The UK’s Health & Safety Executive has warned that the use of climbing frames to “climb” tower cranes can be very dangerous and called for manufacturers to review designs and operating procedures. The comments came in a discussion paper issued by the team that investigated the Canary Wharf accident in which three men died when their tower crane collapsed during a climbing operation on 21st May 2000. Results of the investigation into that accident have not yet been released and are currently being considered by the appointed Coroner.

The HSE paper concluded that “the climbing of tower cranes seems to be a high hazard operation” and focuses its concerns on the fact that during climbing “the whole top of the crane is disconnected from the mast that normally supports it and the load is transferred through the hydraulic cylinder to reaction points on the mast (climbing lugs). The hydraulic cylinder assembly may have to support a dead weight of as much as 100 tonnes, depending on the crane in use. The climbing frame as a whole has to cope with the significant static and dynamic forces involved in climbing”.

This is the crux of the HSE’s concern together with the fact that the use of climbing frames is increasing rapidly. The paper also noted that there is great reliance placed on the experience of a crew operating a climbing frame. This must monitor and react quickly to sudden changes in the operating environment, such as changes in wind direction or speed, as well as ensuring that the crane never slews during the operation. They must also cope with unexpected operational matters such as the new mast section not being correctly aligned.

The document also warned that the actual assembly and disassembly of the climbing frame itself is a hazardous operation: “several serious accidents have occurred at this stage”.

The HSE team cited three serious accidents that occurred in 2001: “The first incident in Italy resulted in the death of an erector during the assembly of a ‘climbing cage’ on a partly erected tower crane. In the second incident, which happened in Australia, a site worker was killed when the 20t counterweight of a crane fell off while the crane was being erected with the use of a climbing frame. The last incident happened in Korea and resulted in the death of two erectors and injuries to others on the ground when a tower crane collapsed during erection using a climbing frame”.

The authors report that an official investigation into a fatal tower crane accident in San Francisco in 1998: “suggests that the immediate cause of that accident was probably the failure of the mast as a result of the crane slewing while a new mast section was being fitted. It was postulated that the erection team had attempted to slew the crane in order to make it easier to push a new mast section into the opening in the climbing frame.”

Sadly the theory cannot be verified as the entire crew was killed in the accident.

The report makes a large number of specific recommendations for crane designers and operators. One is that certified training should be given to supervisors by manufacturers. Another is that it should be impossible to slew the crane during climbing - the HSE reported that current interlocking devices are “easily damaged and can be bypassed by hard wiring the hydraulic cylinder motor into the crane’s electrical supply.”

The HSE has invited comment from manufacturers and users around the world. Comment should be sent by 16 May 2003 to: Andrew East, Construction Sector, Health and Safety Executive, 3SW Rose Court, Southwark Bridge, London SE1 9HS, UK. Tel 020 7556 2100. Email [email protected]

Read the full Consultation Document here