OSHA has not set an exact height that pallets can be stacked. However, 1910.176(b), Handling Materials — General, states that materials stored cannot create a hazard and must be secured from moving. If pallets are stacked too high or are not stable, it can lead to employee injuries, equipment and product damage, and can cause other stacks to tumble in a chain reaction.
Stack empty pallets for both immediate uses and long-term storage. Full and partially loaded pallets are often stacked 2-5 pallets high to save space for temporary product storage or staging before transport. An area with multiple stacks may be difficult to protect from facility traffic, or may create challenges to retrieve pallets from the top. Both scenarios could easily lead to a disastrous situation. Avoid introducing hazards with proper planning and safety considerations.
Local fire codes often limit the heights and aisle widths of empty wood pallet stacks to reduce fuel sources and to prevent hindering fire fighting efforts by firefighters and the sprinkler system. If stacked too close to sprinkler heads, the stacks can impede the minimum 18-inches of clearance required below sprinkler heads per 1910.159(c)(10). The water spray from the sprinkler heads may not cover the entire area it’s designed to protect. Besides OSHA’s requirements, check your local fire marshal and insurance carrier to see if they have any additional requirements.
Numerous factors can impact stacking stability, such as:
- Pallet type (wood, plastic, composite, multiple types stacked together);
- Pallet condition (solid/sturdy, missing boards/supports, crumbling/rotted);
- Pallet size (standard, euro, non-standard, same/different sizes);
- Floor conditions (clean/debris, level/unlevel floor); and
- Location (proximity of other stacks, struck by equipment, ease of loading/unloading).
Pallets loaded with material and product have additional variables that can impact their ability to be stacked safely:
- Load distribution (boxes of different sizes/weights, unlevel top);
- Unsecured loads (unwrapped, loose boxes);
- Box material (thin/thick cardboard, plastic);
- Contents of boxes (partial boxes can create voids, fire hazard);
- Environmental factors (humidity, rain); and
- Transport requirements (customer requests).
Take extra consideration if the stacks are near forklift or pedestrian traffic. Determine if anyone working in the area is at risk if a stack was bumped or falls. Is there a history of leaning stacks or collapses? Can loading and unloading of pallets from one stack impact another?
Ensure your pallets and boxes are in good condition before loading and stacking. Engineered pallets can be safely stacked much higher than ones made from loose parts or a mixture of different wood sizes and strengths. Load pallets uniformly whenever possible and avoid stacking them until immediately necessary, such as for truck transport. Storing pallets in racks is preferred whenever possible.
Stacking empty pallets, fully-loaded pallets, and pallets loaded with everything in-between can be dangerous. However, with proper precautions such as storing uniform materials and using structurally sound pallets, stacking pallets can be done safely.
Key to remember: Deciding how to safely stack pallets is dependent on what is being stacked, how and where it is being placed, and the environment in which it is stored.
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