There is a high risk of musculoskeletal injury linked to the manual handling of heavy roof trusses in teams during their manufacture. These pages describe the key risk factors involved and outline recommendations made by Health and Safety Laboratory (HSL) ergonomists for controlling these risks. Details are also provided of how roof trusses are manufactured and describe mechanical solutions that are available.
Be aware of the key risks
The risks are mainly associated with direct handling of loads that are outside of an individual's capability. There is also the potential for a breakdown in control or coordination of the lifting task. These risks are present throughout all phases of the truss handling operation, ie
- the initial lift from the jig or bed
- the carry over to the stack
- peak-up stacking
See roof truss manufacture for an explanation of these activities.
A further problem is that the working conditions in many roof truss manufacturers are often not suited to team handling tasks. The environment can make it very difficult to coordinate the handling operation if there are:
- high noise levels
- high light levels
- cluttered wood stock piles
- a need to jump down from work beds
- large distances between team members.
The difficulty of communication between team members combined with the heavy, flexible load of the truss and the cluttered workspace means there is a high risk of incidents occurring. For example, operatives may:
- lose their grip on the truss
- slip or trip on an obstacle whilst carrying the truss and make rapid/sudden movements to maintain their balance
- use awkward postures and/or induce large forces at their joints while attempting to recover after a slip
- be carrying more than their share of the load.
Any of these could result in musculoskeletal injury to one or more members of the team.
How to control the risks
The following HSL recommendations will help you to control the risk:
- Keep the area where the trusses are carried clear. In particular, stockpiles of wood should not be placed where team members may have to step across or around them when carrying the truss.
- Operatives should not jump or step from the work beds while supporting a truss. They should put it down until they have got off the work bed. Alternatively, it may be practicable for proper steps or a ramp to be installed to allow safer access off the work bed. However, in many cases this will not be possible because of the travelling press.
- Reduce general noise levels so team members can talk to each other easily. This will allow them to be better at coordinating the truss handling task.
- Where these improvements have been made, teams of operatives could handle the following loads:
- two-person teams - loads up to 48 kg
- three-person teams - loads up to 70 kg
- four-person teams - loads up to 95 kg.
- This team and load information relates to jig and bed truss fabrication methods similar to those shown in Details of truss fabrication
- HSL advises that trusses weighing over 95 kg should not be handled by manual means alone. Some form of mechanisation or mechanical assistance should also be used, as shown in Mechanical solutions.
- 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.
- When there is a four person team, each team member 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.
- Peak-up stacking can be carried out up to a maximum truss weight of 95 kg. The number of people involved should follow the relationship of team members to load, as detailed above. Each team member should have clear and unhindered access to the load.