Logistics versus fire safety in rack storage

Many logistics professionals do not have sufficient knowledge of the implications for fire safety of changes made to the way that goods are stored in warehouses. This article provides some insight into situations to look out for.

If a fire starts at floor level in a storage rack with goods in cardboard boxes on wooden pallets, the flames will reach some eight to ten metres in height in about one minute. The flames cannot get oxygen from the cardboard boxes and stretch upwards in their quest for more oxygen.

A fire like this is impossible to put out with a portable fire extinguisher, and would be very difficult to control even for a professional firefighter with a fire hose. After this first minute, a good fire detection installation with smoke detectors is likely to have just barely detected the fire.

If the fire alarm signal is automatically transmitted to a full-time fire brigade, they will leave the fire station about one or two minutes later. The time of their arrival depends on the distance to the point of alarm. During this time, the fire will continue to grow. A well-designed water sprinkler system will be activated within one and a half to two minutes, and will immediately start to control the fire long before the fire brigade reaches the site.

Well-designed sprinkler system

It is a sprinkler system that follows a recognised standard such as the European standard EN 12845, and that is suited for the type of materials stored, the configuration in which these materials are packaged and stored, and the building's inside height and other installations in the building.

A well-designed water sprinkler system will be activated within 1.5–2 minutes.

What can go wrong?

There are many ways in which a change can negatively affect the ability of the sprinklers to control a fire. These can be roughly grouped into changes in the severity of the fire in the stored material, obstructions that prevent water from the sprinklers from reaching the fire, and changes to the storage configuration.

1. Changes in the products

The automotive industry today uses many more combustible materials than it did 10–20 years ago. As you introduce more plastic components, and in particular more components made of expanded plastics, the fire risk of the goods increases, and the original sprinkler design may not be sufficient. Other examples of an increased fire hazard are the introduction of electronics in ventilation systems and the changeover in hygienic absorbing products from cellulose-based materials to super-absorbent polymers.

2. Changes in packaging

Plastic pallets are used instead of wooden pallets more and more often, for different reasons. The use of plastic pallets increases the amount of plastic in a pallet load, which in most cases results in a need for a higher sprinkler design. In the NFPA 13 standard from the USA, a distinction is made between certified plastic pallets increasing the sprinkler design by one step, and non-certified plastic pallets increasing it by two steps.

Certified pallets are not common in the European market, which is why a change of pallet type could make a large difference if NFPA 13 is followed.

Sprinkler protection of products in cardboard boxes is fairly easy, since the first activated sprinkler will be able to pre-wet boxes that are not yet on fire. Introducing plastic foil wrapping of a pallet of cardboard boxes will, in all sprinkler standards, result in an increased classification, requiring a higher sprinkler design because water can no longer pre-wet pallet loads.

Sensitive products and components are often packed in cut-out protective packaging made of expanded plastics or wrapped in such material. The hazard classification of a pallet is determined by the volume percentage of expanded plastics. The critical volume percentages are lower than 5%, between 5–25%, between 25–40%, and above 40%. Changes in the type of packaging may result in a higher classification.

An important factor for a sprinkler system is that water is able to flow over the outside of each pallet. This means that ESFR (Early Suppression Fast Response) sprinkler designs, with sprinklers at the ceiling only, do not allow the use of so-called open-top containers, which collect the water, or pallets that allow the water to flow through the pallet load and not over the pallets sides, such as SRS plastic trays used in the food retail business. Lower storage heights or in-rack sprinkler installations are the only solutions in these cases.

3. Obstructions to sprinkler water

In a rack, the water must be able to reach all the sides of a pallet at all levels of the storage rack. There must therefore be enough space at either side of pallets standing on the same beam, and between two rows of storage racks, back to back. This opening is called the flue space, and the minimum width varies from zero to 15 centimetres, depending on what sprinkler standard is used and what the storage height is.

It is important that fork-lift truck operators understand the importance of the flue space and that rack arrangements are designed to allow enough space between pallets. An increase in storage height can result in a need to move the storage racks away from each other to allow for a flue space back to back.

Some companies use pallets that are larger than EUR pallets. If dynamic storage locations are used, this allows greater logistical freedom, such as enabling a beam to hold either three EUR pallets or two wider pallets, but this may destroy the vertical continuity of the flue space, allowing water to reach all the way down into the storage rack. Having storage locations for wide pallets only at the bottom of the rack would improve the situation.

All sprinklers are sensitive to obstructions to the water spray pattern from the sprinkler head. New obstructions can typically arise when changes are made to utilities, such as ventilation systems, new light fittings, and so on. Use your contact net to verify whether or not the intended solutions are compatible with the fire protection.

4. Changes to configurations

The introduction of solid shelves could also be seen as an example of an obstruction. Each standard has separate design requirements for solid shelves. There are, however, some loopholes that can be used if you know how to adopt them. For example, NFPA 13 says that solid shelves up to 1.9 m2, or where the shelf design is more than 50% open, are defined as open racks.

If a change-over is made from free-standing storage to rack storage, there may be a need for a higher sprinkler design. This needs to be determined based on information about the goods and the storage height.

A lowered storage height may also be an issue. The sprinkler standards make a distinction between the protection of production areas and of storage areas. In the standards, for storage areas, the maximum distance between the top of storage and the sprinklers is 4–6 metres. If the distance is greater, there are ways to compensate for this. With a high distance, there is a risk that the fire may spread too far horizontally before the sprinklers are activated, possibly overtaxing the sprinkler design area.

In-rack sprinklers are sensitive to changes in the height of the beams in the storage racks. In the worst case, the distribution of water from the sprinklers can be obstructed by the new position of the beams.

5. Compact storage

The use of compact storage systems, in which components are kept in plastic boxes that are stored and retrieved automatically, is becoming increasingly common. It should be noted that this type of storage system is very difficult to protect with water sprinklers unless designed for this purpose from the start. Before deciding on such a system, identify how the store can be protected using either a solution from a sprinkler standard or a solution that has been tested by the store manufacturer.

Managing safely

Try to understand what types of changes may affect the sprinkler installation. Develop a network of good advisers, such as your insurance company, sprinkler contractors, or consultants. It is costly to install a sprinkler system, and any changes afterwards will cost additional money and disturb operations. Try to foresee changes in production and logistical decisions as far into the future as possible. Do not always install sprinklers exactly to suit today's operations, as designing for a higher level from the start may be a low cost compared to making changes afterwards.

Article by

Sören Isaksson

Risk Engineer, If