1.1.3 Stacking and storage

Whatever the nature of your business, it is likely to involve the stacking and storage of goods and materials. Every year accidents occur while goods are being stacked or de-stacked and put into or taken out of storage. Many of these accidents are serious – some are fatal.

Employers must take all reasonable steps to ensure that all goods, materials, substances and equipment in workplaces are so stacked, stored, secured, and kept that they do not constitute a danger to persons in their vicinity during the course of daily operations and in event of a natural disaster such as an earthquake.

Such steps should ensure these items cannot, whether of their own accord, or by virtue of any external force (intentionally applied or otherwise), so flow, move, roll, or collapse, as to constitute a danger to persons in their vicinity.

All workers who are or may be responsible for stacking, storing, securing, or keeping any goods, materials, substances, or equipment require full training in safe methods of doing so.

Given the great diversity of goods and materials to be stored, and the wide range of storage methods and handling equipment in use, how can these obligations best be met?

The answer lies in developing a safe system of work that will integrate the three main components of people, materials and machinery within a safe and healthy working environment. We shall look at each of these in turn.

  • People

People, of course, are the critical factor. In safety and health we are looking mainly at injury and damage to people (concepts of loss control and risk management are not forgotten). Also, it is largely people who perpetrate such injury and damage.

A safe work system relies on:

  • Adequate training and instruction for all the workforce
    • Comprehensive planning, incorporating the views and opinions of those who will operate the systems whenever possible
    • Adequate supervision and control
    • Adequate information to enable the workforce to carry out their tasks in a safe and healthy manner

One way of covering the above is to determine the important criteria for safety and to set specific parameters which may be used, such as planning, the provision of information, training and instruction, and to set the framework for supervision and control.

  • Materials

The basic materials handling and storage systems common to a wide range of stores and warehouses are pallets and racking systems.

Accidents associated directly with pallets occur for five main reasons:

  • Poor pallet design
    • Poor pallet construction
    • Use of an unsuitable pallet for the load or storage method
    • Continued use of damaged pallet
    • Bad handling

There are six main reasons for a racking system failure, either acting singly or in combination:

  • Design fault i.e. rack is inherently unsafe
    • Installation fault
    • Materials handling equipment fault
    • Materials handling equipment operator fault
    • Supervision and control fault
    • Store or warehouse structural fault
  • Equipment

Because of the bewildering range of equipment available in an increasingly competitive market, it is better to simplify the reasons for failure. Basically, accidents occur because of the wrong equipment or overloading of equipment.

General Safety Regulations, 1031 of 1986 states:

8.  Stacking of articles

(1)  No employer shall require or permit the building of stacks which consist of successive tiers, one on top of another, unless —

(a)  the stacking operation is executed by or under the personal supervision of a person with specific knowledge and experience of this type of work;

(b)  the base is level and capable of sustaining the weight exerted on it by the stack;

(c)  the articles in the lower tiers are capable of sustaining the weight exerted on them by the articles stacked above them;

(d)  all the articles which make up any single tier are consistently of the same size, shape and mass;

(e)  pallets and containers are in good condition; and

(f)  any support structure used for the stacking of articles is structurally sound and can support the articles to be stacked on it.

(2)  An employer shall not permit —

(a)  articles to be removed from a stack except from the topmost tier or part of that tier; and

(b)  anybody to climb onto or from a stack, except if the stack is stable and the climbing is done with the aid of a ladder or other safe facility or means.

(3)  An employer shall take steps to ensure that —

(a)  persons engaged in stacking operations do not come within reach of machinery which may endanger their safety;

(b)  stacks that are in danger of collapsing are dismantled immediately in a safe manner; and

(c)  the stability of stacks is not endangered by vehicles or other machinery or persons moving past them.

(4)  Unless a stack is otherwise supported an employer shall take steps to ensure that tiers of stacked material consisting of sacks, cases, cartons, tins or similar containers —

(a)  are secured by laying up articles in a header and stretcher fashion and that corners are securely bonded; and

(b)  are stepped back half the depth of a single container at least every fifth tier or that, alternatively, successive tiers are stepped back by a lesser amount: Provided that at least the same average angle of inclination to the vertical is achieved: Provided further that where the containers are of a regular shape and their nature and size are such that the stack will be stable, they may be stacked with the sides of the stack vertical if the total height of the stack does not exceed three times the smaller dimension of the underlying base of the stack.

(5)  Notwithstanding the provisions of sub-regulation (4), free-standing stacks that are built with the aid of machinery may, with the approval of an inspector, be built to a height and in a manner permitted by the nature of the containers being stacked: Provided that —

(a)  the stacks are stable and do not overhang; and

(b)  the operator of the stacking machinery is rendered safe as regards falling articles.

Some stacking considerations:

  • Floors and Supporting Surfaces

The safe load for every floor should be known and strict supervision should be exercised to prevent this limit being exceeded. As a general rule, a level floor is essential. However, where large stacks are regularly built, it is an advantage if the floor on the site for each stack is given a fall to the centre from all sides. Timber, concrete or other surfacing may be required to support stored materials off the ground. Floors or surfaces required to support stacks, shelving, racks or other means of storage should be capable of sustaining the intended load together with shock loads. If there is a possibility of the stored material becoming waterlogged through rain or after extinguishing a fire, due allowance should be made for this extra weight. The supporting surface should also be sufficiently strong to withstand the effects of any damage to or deterioration of stored materials.

  • Stock Holding Structures

Racks, shelving, bins, hoppers and other structures for the storage of materials should be adequately designed to support and contain the materials for which they are used. Allowance should be made for the possibility of stored materials becoming waterlogged and for shock loads from placing materials or from accidental contact by handling equipment. When partitions are used to increase storage capacity, or to separate stored materials, they should be adequately designed and be of sufficient strength to contain the stored material safely.

Fire-protective partitions should be used between stored items of differing vulnerability to fire.

The corners or ends of shelving and racks should be protected from damage by forklift trucks or mechanised equipment by steel posts, angle irons or other means.

  • Pallet Construction and Loading

Pallets should be of sound construction,   and   be   of adequate strength for the loads and conditions under which they are used. Where pallet loads are stacked tier on tier, the lower pallets should be of suitable strength and in good condition and the unit loads must be able to support the weight above. The stability of stacked pallets or unit loads should be maintained by suitable bonding, avoiding excessive stack heights, to ensure that the contents of any pallet or unit load cannot collapse. The stability and structural strength of each pallet or unit load should be assured by bonding, taping, shrink wrapping or other means. When pallet or unit loads of cartons or sacks are stacked, care should be taken that they are not damaged by equipment. Pallets or other supports used for forming unit loads should be regularly inspected for damage and wear. Items which could cause damage to materials should be taken out of use until repaired, or be destroyed.

  • Positioning of Stacks

Stacks should not be built within 450 mm of a wall. Most building and party walls are not retaining walls and may not withstand the pressure set up by stacks laid against them. A 450 mm gap between the stack and the wall also enables the construction and the condition of stacks to be checked.

Stacks should not be created where any part will be within 1.5 m of a rail track. This clearance should be continued all the way along the stack. Extra care should be taken if the storage area is subject to vibration from rail or road traffic, outside or inside the premises.

Care should also be taken in stacking material near machinery or operations which cause vibrations. Some objects are liable to creep and lose stability under the influence of vibration. Sacks or bales made of synthetic materials are particularly susceptible, especially when first used. (Impregnation with wax can help to overcome this problem.)

Stacks, shelving and other fixtures for holding or storing materials should be so laid out and designed that there is sufficient access for safe loading and unloading by either manual or mechanical means.

Storage areas should be specifically designated, be clearly marked, and be in the charge of a responsible employee. Aisles should be clearly marked, be of ample width for the type of storage, and be kept free from obstacles and waste materials. Stacks should not be created which will block gangways, aisles, walkways, thoroughfares, and particularly doors and exits.

Stacks should have clear spaces of at least 1 m on all sides, apart from walls, where a 450 mm space should be allowed. Goods must not be stacked within 1 m of the ceiling, roof or sprinkler heads. Base areas and heights of stacks should be kept as small as circumstances permit. Goods should be kept well clear of light fittings, heating pipes and appliances, firefighting and alarm equipment, and doors.

No stack, shelving, fixture or other means of storage should be placed in a position, or extended in height, so that a person climbing on to it or removing stored goods, either manually or mechanically, can come into contact with live electrical wiring or unfenced machinery.

No material should be loaded or unloaded from stacks, shelving or fixtures if there is a risk of workers directly or indirectly contacting unfenced machinery, or touching live electrical wiring, until that machinery or wiring is isolated or made safe.

Storage racks and shelves should preferably be non- combustible and not prone to retain water.

Where un-palletised material, which is otherwise secure, is handled by a crane or forklift truck, it should be placed on battens or other devices to aid the use of slings or forks.

Suitable means should be used to protect workers from injury due to sharp corners, projections or edges on structures and/or stored material. Corners of stored material should be clearly marked.

Safe access, by means of ladders, platforms or walkways, must be provided for workers required to climb or remove goods from stacks, shelves and fixtures. On occasions, it may be necessary to erect scaffolding.

Safety belts are useful aids when dealing with high stacks and awkward shapes.

Markings on labels and signs for the identification and selection of materials and goods should be clear and easy to read.

  • Size and Shape of Stacks

The size and shape of a stack depends on the storage space available and on the size, shape, bulk, weight, rigidity or fragility of the articles to be stored.

The following are the most common forms of stack:

  • Column – Single articles placed one above the other
    • Square – Any stack, other than a column, with all sides vertical. (Note the stack does not have to be ‘square’ in the ordinary sense of the word.)
    • Pyramid – A stack in which the plan area is reduced in every succeeding tier
    • Stepped – Stacks with two or more adjacent tiers of the same area and each succeeding group of tiers of a smaller area than the group on which it is set
    • Triangular – Stacks in pyramid or stepped form on two opposite sides, the other two sides being vertical
    • Lean-to-Pyramid or stepped on one side and vertical on the other three sides. (Note the term does not mean that the stack actually leans against a support.)

It is important to remember that the aggregate weight of the stack is borne by the lowest tier, which, of course should be strong enough to bear the superimposed load.

Untidy stacks offend the eye and are rarely safe by construction, since it is usually bad methods of construction that cause the untidiness.

If a stack appears to be unstable, it should be immediately broken down and rebuilt properly.

  • Stability and Bonding of Stacks

Stable construction of the stack is entirely dependent upon the following factors:

  • Safe relation of height to dimension of base
    • Sound interlocking of the goods
    • Contents of the sacks or cartons
    • Compact construction and avoidance of transfer stress in any dunnage used for artificial bonding
    • Shape of articles e.g. meat carcasses
    • Determination of the aggregate weight to be borne by the components in the lowest tier of the stack
    • Good placing of every component forming part of the stack, with special care taken to avoid overhang on any side or end of a stack intended to be vertical

Resistance to collapse, strength and the stability of stacks should be maintained by bonding, stepping, tying or other means. The ratio of height to base dimensions of large stacks  should be  correctly proportioned so that failure of part or whole of the stack does not occur.

Experience has shown that the height to base ratio of an unsupported stack should not exceed 3:1. As most stacks are erected by visual alignment, a slight error in calculation near the base can easily result in a barely noticeable overhang, with a resultant loss of stability. However, where effective bonding can be achieved, and where there is a good frictional grip between the contacting surfaces, the ratio of height to base can be safely increased to 4:1.

The shape of goods or packages to be stacked will have a great bearing on the type of bonding used. When one dimension is appreciably greater than the other two, it will be possible to use natural bonding, i.e. to secure stability by interlocking the articles themselves. In other circumstances it will be necessary to introduce other materials (e.g. canvas sheets, battens, piling sticks, etc.) to prevent movement of the articles stacked: this is known as artificial bonding.

Outdoor stacks are affected by weather conditions such as rain, wind, frost and  sun.  These conditions can greatly influence the stability of stacks over time and should be taken into consideration. Materials which could be dislodged or blown off the top of a stack under windy conditions should be tied down or otherwise restrained. If tarpaulins are used to secure or protect the stacks, they should be fastened to independent anchorage, not to the stack itself.

Stacking Different Types of Goods

  • Bagged goods

The first tier should be so arranged that the bags can be spread flat, and the same should be done in succeeding tiers. Interlocking should be used if possible. Where possible, the mouths of the bags should be on the inside of the stack. Bagged material of differing sizes and shapes (e.g. seeds, granules, pellets etc.) should not be stacked on top of each other unless proper precautions are taken to prevent movement by settling or vibration. Pallets with spacers or some form of horizontal bonding should be used if there is a risk of such movement or if it is intended or necessary to stack high. Special precautions should be taken with synthetic bags or sacks, which have a tendency to slip when new.

  • Cartons – Careful consideration should be given to the weight of stacks of cartons. Dampness will reduce the strength of cartons, and a damp flow may well lead to damage of the lowest tier and ultimate collapse of the stack. Interlocking (e.g. the bricklaying method) can be used in stacking cartons.
  • Cases (boxes) – As most boxes are reinforced with external battens, care should be taken to see that the battens bear the weight, not the box.
  • Bales – Bales should be stacked with care to ensure their stability. Attention should be paid to possible vibration, and if possible stacks should lean into their centre. Extra care should be taken with synthetic bales, which have a tendency to slip when new.
  • Frozen carcasses – Because of their shape, carcasses lend themselves to a form of interlocking and this method should be used if possible, together with pallets with spacers or some form of horizontal bonding. A suitable type of mesh netting can be used to retain carcasses on pallets if necessary, provided it meets hygiene requirements.
  • Coiled wire – Coiled wire may be stacked horizontally or vertically. Wedges or other supports must be used to prevent the stack from spreading.
  • Glass bottles and jars – Care should be taken stacking bottles and jars, whether full or empty. Small quantities can be laid on their sides on top of each other, using wedges as necessary. Otherwise they should be stacked in cases, boxes, cartons or racks designed to hold them. If pallets are used, spacers or some form of horizontal bonding should be incorporated. The overall weight of stacks should not be borne by the glass itself.
  • Drums, casks and cylinders – Drums, casks and cylinders may be stacked on their sides or ends unless specifically required to stand upright on instructions from their manufacturer or supplier, e.g. acetylene cylinders. If stacked on their sides, wedges should be fixed at the ends of each row to prevent movement.

If gas cylinders are stored on end, restraining chains should be fitted to prevent them toppling. The valves of gas cylinders under pressure must always be protected.

Power-operated clamps on forklift trucks enable cylindrical objects such as cable drums or pipes to be stacked on end, allowing greater economy of space and greater stability.

  • Sheet  materials – Sheet materials, including glass, may be stacked flat or on edge. Sharp edges should be protected to prevent injury to workers and passers-by. The supports used in edge-on stacking must be of adequate strength to bear the side thrust of the vertical sheets.

Extra care should be taken when stacking and handling glass. Owing to the weight of metal and glass sheet in bulk, care should be taken not to overload racks and the floor.

  • Steel tubes bars and joist sections – Suitable racks should be provided for steel tubes, bars, joist sections and similar materials. Large-diameter tubes or pipes can be stacked on their sides, as for drums.

Wedges, chocks, stakes or other means should be used to restrain the bottom tier of round objects which are stacked or tiered and which could cause the stack to collapse by rolling or moving.

Where successive tiers are not nested but rest on battens, planks or other flat surfaces, they should be restrained from moving by wedges secured to the battens or planks.

Where the collapse of a stack or tiers of round objects could cause damage or injury, material to be removed should always be taken from the top of the stack or from the top tier first.

  • Chemicals and other hazardous materials – All hazardous chemicals must be stored in secondary containment.  Hazardous chemicals should be segregated in separate cabinets by hazard.  If space does not allow, incompatible chemicals may be stored in the same cabinet when secondary containment is used to prevent any spilled materials from contacting incompatible containers in the same cabinet.  To assist in proper segregation of chemicals, the following guide may be used:

Be aware that if segregated acids and bases are stored in the same cabinet, the off-gassing from the containers will cause any metal inside the cabinet to rust.  Over time, this may lead to shelving brackets to rust through and hinges damaged.

A standard practice is to compile a list of incompatible chemicals as per the example below:

The pictogram below shows a design for a typical flammable material storage cabinet.

Outside storage for these types of materials often has special designs as per the photo below:

Rules for de-stacking

  • De-stacking is largely the reverse process of stacking. Most accidents involving the collapse of stacked materials occur during de-stacking. The prime cause of this is haphazard removal.
  • Basic rules for breaking down stacks are:
    • One person only should be responsible for the manner in which the stack is reduced. This is particularly important where gangs are employed.
    • If the person in charge of de-stacking had no part in erecting the stack, he or she should ascertain its construction before work begins
    • The stack should be taken down tier by tier, so that no part is in danger, as would happen if the stack were bitten into locally
    • When a large stack has been given a natural fence by building the periphery higher than the centre, this fence should be maintained during de-stacking. The work should be done outward from the centre, reducing the periphery last so that there is a barricade to prevent people falling off. If tubular or other fencing has been built in or around the stack, it should be dismantled and adjusted as the height is decreased.
    • As there is a high tripping hazard in the working area of a stack, tidiness and systematic work methods are essential
    • Care should be taken to ensure that people working on stacks are at all times clear of overhead travelling cranes. Proper signalling arrangements should be made and a lookout should be posted.
    • All de-stacking should be carried out under competent supervision