Tower crane
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Tower crane collapse events

Risk management

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    The risk of tower crane collapse events can increase due to associated adverse weather, particularly during the winter months

    Although there are many different  types and configurations of tower  cranes, the most common types we  see consist of a tower section located  on a fixed base with a jib attached to  the tower via a slew   mechanism. This  mechanism allows the crane operator,  through a gearing arrangement, to  slew the jib around the construction  site and then hold the jib in position via  a slew brake. In normal operation, the  slew brake is always engaged and the  operator, through his control inputs,  disengages the brake and moves the  jib to the required position. The brake  is then re-engaged until the next  control input.

    When the crane is left unattended, it is  usually a requirement to leave the slew  brake disengaged. This allows the jib  to move freely and weathervane with  the wind. Allowing the jib to move  freely greatly reduces the stress  imposed on the tower section and jib  section. However, if this brake is engaged in a period of high wind, the stress imposed upon the structure can lead to failure. This is a particular risk  during winter months.

    Risk management: Health &  Safety Executive guidance

    The Health and Safety Executive  (HSE) have investigated crane collapse  events and subsequently   provided  guidance (available at bulletins/luffing-jib-towercranes.htm).  This   document advises the following  for all tower crane users:

    • Ensure the most accurate up-to-date  information is being used for the  specific crane they are operating.  This may include discussions or  correspondence with the supplier or  manufacturer as some  manufacturers may have changed  their guidance.
    • Check that the information includes  the correct minimum out-of-service  radius for the specific crane being  operated.
    • Check, both after erection and  periodically in-service, the function  that releases the slew brake and  places the crane in free slew.
    • Check, both after erection and  periodically in service, that the  condition of the slew drive motors,  gearboxes and slew ring bearing  have not deteriorated to the extent  that the crane is prevented from  slewing freely.
    • Check, both after erection and  periodically in service, the setting  and function of any devices that warn  the operator that the crane jib has  not been left parked at the correct  out of service radius and/or the slew  brake has not been released.
    • Ensure that operators have been  provided with instructions on how  the crane should be placed in free  slew and the correct radius at which  the jib should be positioned when  leaving the crane unattended. This  should include measures to routinely  check that the operators understand  and are following the instructions  provided.
    • Undertake periodic checks that the  buildings under construction, other  cranes or high reach plant are not  preventing the crane from free  slewing. Consideration needs to be  given to both front jibs and rear  counter jibs.

    Key risk measures

    Crane owners/users should have a  robust planned preventive  maintenance (PPM) system along with  prescribed safety checks. Detailed  requirements and checklists are  included in BS7121-2-5, the Lifting  Operation and Lifting Equipment  Regulations (LOLER) and the Provision  and Use of Work Equipment (PUWER)  Regulations, as well as detailed guides  produced by the Construction Plant-Hire Association (CPA) including  TCIG-0801.

    Pre-use checks, regular in-service  inspections and maintenance checks  are essential and need to be recorded.  Key aspects to check during  maintenance include (but are not  limited to):

    • general condition of structures (e.g.  fatigue cracks), fastenings, ties and  machinery  
    • operation of alarms, warning lights,  indicators, motion limiters and   cab  accessories
    • presence of documentation and  warning signs
    • slewing mechanism, control gear,  safety devices, cables and pulley  block

    In addition to a PPM system, cranes  also require periodic thorough  examinations as prescribed by LOLER.  The thorough examinations would  need to be carried out at:

    • specified intervals
    • after installation
    • after major alterations or repair
    • after exceptional circumstances  affecting the safety of the crane (e.g.  adverse weather conditions)

    Examinations need to be undertaken  by a Competent Person.

    Construction insurance solutions and inspection services

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    Our engineering inspection services also help customers to maintain workplace equipment safety, optimise the efficiency of a vast range of plant and equipment, and comply with applicable health and safety legislation.  Our team  of technically-experienced Engineer  Surveyors can perform the role of 'Competent Person' on tower crane  inspections.