Safer timber stacking and storage
The UK Health and Safety Executive has issued a warning on the dangers that can arise from the unsafe stacking of timber. Cliff Seymour, Her Majesty’s Inspector of Health and Safety, reviews guidance on safe practice.
Falling timber is one of the main causes of fatalities and serious accidents within the woodworking industry, yet the risks posed by stacked timber are often underestimated. It is, therefore, an opportune time to review the guidance and research on safe stacking and storage that is available for round and sawn timber, as well as wood-based sheet materials.
The long and short of it
The use of a loader with grab attachments is the safest method of stacking, de-stacking and transporting logs, as this avoids any need for workers to be on or near the stacks for slinging.
Log stacks should not normally be higher than the length of the logs they contain. The height should also be limited to within the safe range of the grabber. The maximum stacking angle should be 45º, but, if it is not possible to keep stacks separate from workers, then the angle should not exceed 35º. In addition, wedges should be used to fix the logs and prevent them from rolling.
The following factors will increase the risk of a stack collapsing –
- Sloping ground causing logs to slide from the stack or roll down the slope.
- De-barked logs which are slippery, particularly if recently cut.
- Logs stacked with their butt ends to one side of the stack so that the angle across the top of the stack causes logs to slide off, particularly if de-barked.
- Logs stacked on soft ground sinking on one side and becoming unstable.
Where any of these conditions are present, consideration should be given to reducing the stack height or preventing movement of the logs by containment, either in bunkers or by the use of stanchions.
Sawn timber stacks
Good quality packs are needed to build a stable stack. Packing the same type of timber together to remove internal air space and using suitable sticks to bind layers of timber will improve pack stability. Signs of broken or loose banding, lozenging, balling and internal collapse are all signs of poor practice when producing packs. Any out of shape or collapsing packs should be identified before being placed in a stack. Otherwise, they will need to be safely removed before being rebuilt.
Packs should not contain any varying lengths of timber as these can provide footholds for climbing the stack, a practice that should be prohibited. Protruding timber can also be a danger to persons or vehicles. If access to the top of stacks is required then it must be done safely. If no appropriate plant is available, a secured or footed ladder can be used, provided the stack has been checked for stability and the area has been coned off. Any de-stacking should be carried out from the top down, tier by tier, with care taken to maintain stability and check for any signs of movement.
Stacks should not be allowed to lean on each other, as during de-stacking, forces will be exerted on the adjacent stack/s and may cause collapse.
To remain stable, the packs must stay intact and not be subjected to any forces caused by wind or unstable ground conditions.
As a general rule, calculations have shown that stacks with a height-to-base ratio of 4:1 will remain stable provided that –
- The packs are banded to a high quality.
- They are on hard standing or on stable ground.
- They are located in an area where risks from impacts and other external forces are low.
If such forces cannot be eliminated, then the height-to-base ratio of the stack should be reduced to 3:1 for an indoor stack and 2:1 if external.
Packs should also be square or rectangular in cross-section with centres of gravity directly over the centre of the bottom pack. Larger heavier packs should be placed at the bottom. Packs should not be placed so that they cause bridging between stacks.
Packs can become unstable if there is the wrong type of banding, incorrect band tension, and incorrect application (out of square).
Banding should be in good condition and placed as close as possible to the columns of sticks within the pack, (see main image top). Regular checks should identify any damaged bands, clips or buckles so they can be replaced. If this requires the removal of a pack from a stack, then this should be done safely. Eye protection should also be used when any banding material is cut. Recurring problems should result in a review of banding methods.
Storage areas should ideally be flat, with any slope not exceeding two degrees (a slight slope along the length of the stack will allow water to drain off). Concrete, asphalt and hard standing are the best ground for stacks. The ground surface should be strong enough to avoid cracking or breaking up under load or with wear. It should also be well drained.
Bearers and separating sticks should be square or rectangular in section, uniform and in good condition. There should also be a good supply of them as often unsuitable ones end up being used. The bearer’s cross-section should allow access for the forks of a forklift truck (FLT) or side loader. The length of the bearers and sticks should be the same as the width of the packs in the stack. Enough, bearers and sticks should be placed along the packs length to prevent the timber sagging. As with the banding, there should be a procedure for identifying and replacing poor or damaged bearers.
Packs should be transported a minimum number of times as internal stability can deteriorate when a pack is moved. The yard layout should allow safe access and egress for FLTs to each stack. Visibility can be improved by the use of mirrors and lighting around the site or on vehicles. Site layout should also take account of the prevailing wind directions and any micro-climate issues, for example, where buildings or geographical features may be relevant.
Wooden sheets generally have a standard size of 2,440 x 1,220mm (or divisions of) and can range in thickness from three millimetres to 35mm. A single 18mm-thick plywood sheet of this size weighs approximately 30kg. It is easy to lose control of such large heavy sheets when they are being moved. This problem is made much worse when they are stored together in a stack leaning against a wall and several sheets fall at once. Purpose designed storage racking should be used and this is relatively easy to construct and can often be made in-house. Appropriate handling aids should be used when moving sheets.
The serious consequences to a worker and his employer following a fall of sheets are shown in the Health and Safety Executive DVD – Health and Safety in the Woodworking Industry www.hse.gov.uk/pubns/books/woodworking-dvd.htm
Health and Safety Laboratory reports – Stability of stacked logs, ME/98/25, and Safety of Timber Stacks – Stability of Sawn Timber, ME/99/25: www.hse.gov.uk/research/hsl/engineer.htm
Video showing good practice when handling boards www.hse.gov.uk/woodworking/manualhandling.htm
Woodwork Information Sheet No.2 – Safe stacking of sawn timber and boards available from www.hse.gov.uk/woodworking/workplacemanage.htm