Tower Crane, Slew Brakes and Release Mechanism Maintenance
Health and Safety Executive - Safety alert
FOD CD Construction Policy and Sector Unit
Tower crane owners and users, maintenance personnel and thorough examiners, Construction, Engineering, Entertainment and Leisure, HID, Manufacturing, Nuclear, Off Shore.
Preventing catastrophic failure of tower cranes: essential inspection and maintenance of crane components including slew brakes and their release mechanisms; reference marking of crane components; maintenance documentation; placing tower cranes in a safe out of service condition; and signs/banners on cranes.
HSE is investigating the collapse of a tower crane jib in high wind. The precursors of the incident are not fully determined at this point but investigations to date suggest that problems with adequate maintenance of the slew brake release mechanisms and the addition of accessories were contributing factors. We would remind all tower crane owners and users of some precautions and procedures that should be followed to ensure that risk of collapse or overturn in high wind is minimised.
This safety alert advises on the steps to be taken to ensure that tower crane slew brakes and their release mechanisms are maintained in an efficient state, in efficient working order and in good repair and to ensure that the addition of accessories to the tower crane structure do not compromise the free slew characteristics of the jib such as to contribute to the potential for collapse. This information is issued without prejudice to any ongoing investigations.
This alert provides supplementary information to HSE Health and Safety Bulletins:
Tower Crane Inspection and Maintenance history
Investigations have found that inspection and maintenance history for some tower cranes do not always take into account exchange of individual component parts.
Some tower crane designs incorporate more than one slew motor, each having an independent slew brake and release mechanism. Such systems can deteriorate in performance during their operation over time and a crane's slew motor brakes and their release mechanisms can deteriorate at different rates.
It is therefore vital that a crane's slew motor brakes and their release mechanisms should be kept in an efficient state, in efficient working order and in good repair. All the crane's slew motor brakes and their release mechanisms should be inspected at the same time and maintained accordingly in order to ensure the entire on-board slew brake system operates effectively.
When a crane design incorporates duplicated components ie slew motors, slew brakes, slew brake mechanisms, identifying which component has been inspected, maintained, deteriorated etc. proves difficult to record, action or trace if the component has no marking.
Crane components ie slew motors, slew brakes, slew brake mechanisms, should contain unique reference markings to enable component identification and traceability throughout inspection and maintenance regimes and these individual identifiers should be traceable in any associated documentation. If they have no such identification then that needs to be remedied, using permanent and indelible markings.
Crane inspection and maintenance documentation should ensure individual crane components can be identified and for associated inspection and maintenance information/observations/measurements to be recorded against that component ie if the crane design includes two slew motors then the inspection/maintenance document should provide the facility to record both slew motor/brake identification markings, their respective slew brake information/observations/measurements etc.
There needs to be a system in place to ensure that where slew brakes, motors, etc. are interchanged between cranes that their service history is reassigned and traceable to that new crane.
There is often a requirement for the fixing of floodlights and signs to the structure of tower cranes. Such additions to a crane structure will increase the structures wind area and hence the wind force on it. Any additional wind area may also prevent an out-of-service crane from free slewing downwind.
Investigation has identified that advertising signage affixed to a crane's upper structure affected the crane's overall slew performance. The crane manufacturer's approval should be obtained before any such signage additions are made. The position and fixing of all signage, floodlights and advertising media should also be in accordance with the crane manufacturer's specifications.
Attachment brackets for tower crane accessories including signage should be designed and checked by a competent person using an appropriate crane design standard. The crane manufacturer should be consulted to ensure the crane structure will safely absorb the loads imposed by the bracket.
Those who own, use, inspect, maintain tower cranes must ensure that:
- A tower crane's slew motor brakes and their release mechanisms should all be inspected at the same time and maintained to ensure the same efficient state, efficient working order and good repair.
- Tower crane components ie slew motors, slew brakes, brake mechanisms, should contain unique reference markings to enable component identification and traceability throughout inspection/maintenance regimes.
- Tower crane components should be traceable in any associated inspection and maintenance documentation.
- Inspection and maintenance documentation shall permit individual crane component reference markings and all information/observations/measurements to be recorded against that component.
- The inspection and maintenance system permits the re-assignment and traceability of crane components between different cranes.
- Size and location of crane signage, advertising, posters, illuminated media etc. should meet with the crane manufacturer's approval and specifications before any such additions are made.
Those who own, use, inspect, maintain tower cranes are reminded that:
Relevant legal documents:
- Sections 2 & 3 of the Health and Safety at Work Act 1974
- Provision and Use of Work Equipment Regulations 1998,
- Management of Health and Safety at Work Regulations 1999
Health and Safety Executive
Construction Division Safety Team
151 Buckingham Palace Road,
London SW1W 9SZ
Please pass this information to a colleague who may have this Product/ Equipment or operate this type of system/process.