Block Stacking and Pallet Rules

What is block stacking, and why are stacking rules written separately?

Block stacking means placing palletised loads directly on the floor and on top of each other, without racking. It is the most common form of storage in raw material stores, buffer areas before dispatch and yards that fill up in busy periods, and it cannot be managed safely without its own stacking rules. In racked storage, each pallet sits on its own beams; in block stacking, the weight of the top pallet passes down through all the tiers in between and bears on the bottom box and pallet.

This difference explains why the rules must be written separately from racking rules. For racking, you look at the capacity label; we cover racking safety in our article on industrial racking safety. In block stacking, however, capacity is determined by the packaging itself, and this capacity can change within a day with humidity, storage time and damage. A stack collapse often starts not with a forklift impact but with the bottom box being slowly crushed over weeks.

The employer's obligation to carry out a risk assessment comes from Art. 4 and 10 of Law No. 6331 on Occupational Health and Safety. There is no single figure for stack height that fits every load; so you set the height using the criteria below during the risk assessment and put it into a written rule.

What determines stack height?

Stack height is limited by the weakest of five factors:

1. Stacking strength of the packaging: the maximum top load declared by the box or packaging manufacturer. If this information is not available, ask the supplier for it; it is the foundation of the stacking rule.
2. Condition of the pallet: a single broken board on the bottom pallet can cause the whole load above it to lean.
3. Floor: a stack built on a hollow, slope, joint or manhole cover starts at a slight angle at the base, and this angle grows as it gets higher.
4. Forklift reach and visibility: the height at which the operator has to place the load without seeing the top tier is the limit of the stack.
5. Building conditions: ceiling lighting, the design conditions of fire detection and sprinkler systems, and door openings may limit stack height from below.

Worked example (with representative values): suppose a box manufacturer has declared that a maximum of 600 kg can be placed on top of a single pallet load. The gross weight of the pallet is 250 kg.

On paper, the table shows that three tiers are possible. However, the strength of cardboard packaging falls markedly with humidity and long storage times. For a stack coming out of cold storage, waiting on a ramp in rainy weather or left untouched for months, do not rely on the full declared value; ask the packaging manufacturer about strength under these conditions. It is more accurate to write the rule as conditional, such as "maximum 2 tiers for this product, 3 tiers in a dry area", rather than "maximum 3 tiers".

The second calculation concerns slope. A slope of 1 degree at the base corresponds to a shift of about 7 cm at the top of a 4-metre stack; 2 degrees to about 14 cm (4 m × tan 1° ≈ 0.07 m). A stack that looks "slightly crooked" to the eye may be close to leaving half a pallet unsupported at the top tier.

Damaged pallets: which ones do not go into a stack?

A damaged pallet is the weakest link in block stacking, because the defect is often under the bottom load, out of sight. Before putting a pallet into a stack, look for these defects:

Move damaged pallets to a marked quarantine area and prevent them from returning to the floor until a decision on repair or disposal has been made. Leaving damage reporting to forklift operators is not enough; goods-in and dispatch staff should also have the authority to stop work when they see a defective pallet.

How does a stack collapse start?

A stack collapse usually happens when several small defects combine. The most common causes in warehouses are:

• Mixed pallet sizes: when pallets of different sizes are stacked on top of each other, the upper pallet overhangs at the edges and the load bears on a single edge.
• Uneven load: boxes piled up on one side of the pallet shift the centre of gravity. Distribute boxes evenly on the pallet and do not let them overhang the edges.
• Loose stretch wrap: a pallet with torn or insufficient wrap comes apart during handling.
• Crushed bottom box: a swollen, bulging or corner-crushed bottom box is a warning sign of collapse.
• Forklift impact: a fork or mast hitting a stack that protrudes into the aisle moves the bottom pallet.
• Floor and weather: wind in open areas, pallets slipping on wet floors and stretch wrap loosening in the summer sun are additional risks.

Look for these signs on a weekly stack walk, and do not leave a leaning stack "for now"; take it down in a controlled way, starting from the top tiers.

Layout of the pallet stacking area

A good block stacking area makes it easier for the rules to be followed as a matter of course:

1. Floor marking: mark the boundaries of stacking blocks and aisles with floor lines. Stacks must not protrude beyond the line into the aisle.
2. Stack card: at the head of each block, post a card stating the product, the maximum number of tiers and any special condition (for example "2 tiers in humid periods").
3. Aisles: plan the width the forklift needs to turn and the pedestrian route together. For separating pedestrians and vehicles, our article on forklift and pedestrian traffic plans in warehouses is a guide.
4. Escape routes and fire equipment: under no circumstances is anything stacked in front of fire hose cabinets, extinguishers or emergency exits. Designate temporary stacking areas for busy periods in advance; our article on OHS in e-commerce warehouses also addresses this problem.
5. Lighting: the operator must be able to see the top tier and the pallet's fork pockets clearly.

Warehouses around the port and free zone in Gemlik, and the dispatch areas of industrial plants in Bursa and the surrounding provinces, are places where block stacking grows quickly in busy periods. Putting the rule in writing for these areas ensures that temporary workers follow the same practice.

Manual stacking and palletising

Not every tier of a block stack is built with a forklift. Mixed boxes arriving at goods-in, orders re-palletised before dispatch and loads transferred from damaged pallets are often stacked by hand. This work directly affects both the stability of the stack and the worker's back:

• Heavy boxes at the bottom: when building a pallet, put heavy, sturdy boxes in the bottom layer and light, fragile ones on top. A pallet built the wrong way round starts to lean as the bottom box is crushed.
• Interlocking pattern: lay boxes in each layer rotated so that they cover the joints of the layer below. Boxes stacked directly on top of each other behave like independent columns and separate easily.
• Overhang: boxes must not overhang the edge of the pallet. An overhanging edge reduces the load-bearing strength of the packaging and tears as it rubs against the neighbouring stack.
• Working height: building a pallet at floor level forces the worker to bend constantly. An adjustable pallet lifter or turntable allows the bottom layers to be built at waist height.

For manual lifting limits and correct lifting technique, see our article on manual handling and lifting technique.

Rules for forklift operators and stackers

• Bring the forks level before placing a pallet on the stack; do not set the load down while the mast is tilted back.
• Place the load only directly on top of the pallet below, with the edges aligned.
• Do not raise or lower the load while there are pedestrians next to the stack.
• Do not climb on the stack or use it as a ladder.
• When you notice a damaged pallet, stop work and report it to the person in charge.

For the checks the operator carries out before starting work, see our article on the forklift operator's daily check; for those working with stackers, see pallet trucks and stackers. Under Annex III of the Work Equipment Regulation, forklifts undergo periodic inspection at least once a year; you can track inspection dates with the OHS calendar.

In our OHS specialist service, we write stacking rules according to the products on site and carry out the walk-round checklist together with the warehouse manager. Our approach to warehouse and logistics businesses is on our logistics and warehousing page.

Frequently Asked Questions

How many tiers of pallets may be stacked in a block stack?

There is no single number of tiers that applies to every product. The limit is set by the declared stacking strength of the packaging, the soundness of the pallet, the floor and the forklift's reach. Use these criteria to set the maximum number of tiers for each product and write it on the stack card.

Can a damaged pallet never be used?

Pallets with broken top boards, missing or cracked blocks, or cracks in plastic should not be stacked. For lighter defects, the pallet is moved to the quarantine area and a decision on repair or disposal is made; it does not return to the floor until the decision has been made.

Can we spot a stack collapse in advance?

Often, yes. A leaning stack, a swollen or corner-crushed bottom box, torn stretch wrap and a pallet protruding into the aisle are early signs. Look for these signs on the weekly walk and take down a leaning stack starting from the top.

Can block stacking be done outdoors?

It can, but wind, rain and sun bring additional risks. Wet cardboard packaging loses its strength and the ground becomes slippery. Keep the number of tiers lower outdoors and check stacks again after bad weather.