SIM 03/2009/01
There is a high risk of musculoskeletal disorder associated with manual handling of heavy roof trusses in teams. This SIM describes the key risk factors and outlines recommendations by Health and Safety Laboratory ergonomists. For example, trusses over 95 kg should not be handled by manual means alone. Mechanical solutions are described
1 Work by the Health and Safety Laboratory (HSL) has shown there is a high risk of musculoskeletal disorder associated with team manual handling of heavy roof trusses during fabrication. The analysis was produced in support of a prosecution where a man was seriously injured after being struck by a heavy roof truss, and to support enforcement action taken by the investigating inspector.
2 Provision of mechanical handling equipment to reduce the risk of manual handling injury during handling of roof trusses has been shown to be reasonably practicable. The Sector has photographs and in one case video images from several different installations. An appeal against an Improvement Notice to provide mechanical handling equipment, where heavy trusses were being made, was unsuccessful.
3 After timber for the truss has been cut to size, the truss is assembled and pressed. There are broadly two methods of truss fabrication:
(1) The jig method: This utilises a set of independently moveable jigs (approximately 800-900 mm high) onto which the timber members are placed /supported (at the joints). Timber members are clamped in place with nail plates positioned across the joints on each side of the wood. When the truss is configured correctly a press is used to compress the nail plates into the wood, securing the joint.
(2) The work bed method: This consists of a large flat bed and a travelling press head. The bed heights range from 590-840 mm high. Timbers are laid out on the bed and clamped/secured in position. A nail plate is positioned either side of each joint. Once assembled, a gantry-mounted hydraulic press moves down the length of the work bed and exerts pressure onto the press plates one at a time, fixing the timbers in position.
4 In both cases once the nail plates have been pressed the truss is released and lifted off the jigs/bed by teams of operatives, then carried to the stack. Trusses tend to be stacked with their peaks upwards (peak-up stacking). The stacks are banded and then typically removed by side loader.
5 Trusses can vary a great deal in size and shape. There are several configurations, for example: attic, duo-pitched, single pitched, and laminated (or plied). Trusses can measure from a few metres wide and high, to 20 m long and 5 m high.
6 Most fabricated trusses weigh below 75 kg, typically in the region of 50-70 kg. Some single trusses can weigh as much as 150 kg and if plied together with another up to about 200kg. Attic trusses are particularly heavy, they have large timber members to make up for the lack of triangulation timbers that would interfere with the habitation area.
7 There is a high risk of musculoskeletal disorder associated with the team manual handling of heavy roof trusses during truss fabrication. This is mainly associated with direct handling of loads outside of individual capability and with the potential for a breakdown in control or coordination of the task. The risks are prominent throughout all phases of the truss handling operation (eg the initial lift from the jig/bed, the carry to the stack and peak-up stacking).
8 The conditions in many truss fabrication plants are not suited to such a demanding team handling task. The environment (eg noise, light levels, wood stock piles, jumping down from work beds and distance between operatives) makes it very difficult to coordinate the handling operation.
9 The difficulty in team member communication combined with the heavy, flexible load and the cluttered workspace means there is a high risk of incidents occurring. For example, operatives lose grip, attempt to recover (using large forces and/or awkward postures) or be expected to take a disproportionate amount of the load. Occurrences such as these could result in musculoskeletal injury to one or more members of the team.
10 Measures should be introduced to reduce the risks of musculoskeletal injury associated with the team manual handling of roof trusses using the following recommendations:
11 Under circumstances incorporating the improvements set out above, teams of operatives could handle the following loads:
These relate to jig and bed fabrication methods identical or similar to those described in paras 3-6.
12 Trusses over 95 kg should not be handled by manual means alone. Some form of mechanisation or mechanical assistance should also be used.
13 Teams of five persons or more should be avoided; the extra team members do not contribute much more and may make the team difficult to coordinate properly.
14 The use of four person teams must relate to the size of truss to be handled, operatives must have good access to the load, at a convenient lifting position. The use of a four-person team may not be suitable for smaller trusses.
15 Peak-up stacking can be carried out up to a maximum truss weight of 95kg. The number of people involved should follow the relationship of team members to load set out above. Each team member should have clear and unhindered access to the load.
16 Mechanical handling systems are available for moving fabricated trusses. Two methods shown to work are known to the Sector:
17 The Sector has heard from industry that swinging arm floor mounted cranes are used in at least one factory. We would be grateful for further information.
18 This information is in addition to the guidance within the MSD FOD Inspection pack [519KB]. Also refer to the Manual handling risk assessment flow charts (MAC) (OM 2002/122) where local factors may make the work higher or lower risk, eg heavily restricted posture, contaminated floor.
19 Ask the company about the range, size and weight of trusses they produce. Usually the design software being used gives the total weight of the truss.
20 Compare the number of individuals in the team lifting heavy trusses with the HSL recommendations above. Also look at the working environment where trusses are being handled.
21 Examine the companies RIDDOR history and accident book for handling related accidents/ill-health.
22 Consider enforcement action to provide mechanical assistance where heavy trusses over 95 kg are being handled by manual means alone. Enforcement action may also be appropriate for less heavy trusses where team numbers are not sufficient or the premises/working environment increases the risk of injury. See Enforcement Management Model guidance.
23 Consider levels of instruction and training. The risk of injury is increased if incorrect lifting techniques are being used.
24 Inspectors should be aware that the Sector has held meetings with the Trussed Rafter Association (TRA). The TRA represents many roof truss manufacturers. It is aware that improvement notices have been served on this issue. Recently, the health and safety committee of the TRA reported to members that HSE "...is pushing strongly for compliance with manual handling standards..." and that "members ought to have taken some action by mid 2003 or they may come under very great pressure from HSE"
25 This guidance is based on the Enforcement Management Model (EMM) Version 3.0.
26 Immediacy of risk - Failure to provide mechanical handling equipment, or having team numbers smaller than the HSL recommendations, should not normally be considered an immediate risk of a serious personal injury.
27 The benchmark is compliance with the Manual Handling Operations Regulations and the additional information given in this SIM. Use the single casualties tables. Where roof trusses greater that 95 kg are being handled the benchmark is: Serious Health Effect - nil/neg
28 The following are relevant when deriving the authority of standards. Which standard(s) is/are relevant when applying the EMM depends on the change in behaviour or activity you are seeking to achieve, ie whether the change you want is documented in a defined, established or an interpretative standard.
| Title | Authority |
|---|---|
| Manual Handling Operations Regulations 1992 | Defined |
| SIM - Manual handling in teams during the fabrication of roof trusses | Interpretive |
29 Inspectors are asked to bear in mind the seriousness of manual handling injuries. The Sector contends that the contribution from installing a properly engineered lifting device to reduce the risk of injury is not grossly disproportionate to the sacrifice (money, time and effort) needing to be made by the employer and thus is 'reasonably practicable'.
30 SIM 03/2003/69 – cancel and destroy.
