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Figure 1. Longitudinal and transverse flue spaces. Longitudinal spaces are those between racks at the left. Transverse flue spaces, on the right, exist between stored materials and the racks as one is facing them. These flue spaces should be maintained to allow vertical fire spread and enable fire control water to reach burning and nearby combustibles. IL certifications can be an important factor in processors’ efforts to protect human life, plant assets and business operations.

High challenge: High-piled storage fire protection – Part 1

Rising real estate costs and materials handling improvements make high-piled and rack storage a desirable option for product manufacturers and wholesale companies. With multi-function scanning codes and radio-tracking tags, warehouse operators can manage a huge variety of commodities in vast buildings with items stacked as much as 30 m (100 feet) high.

This modern storage approach, however, is not without inherent fire risks. High-piled and rack storage concentrates fire loads per unit of floor area and trades the problem of horizontal fire spread for vertical. Fires in rack storage configurations can radiate across aisles or travel through obstructed flue spaces and appear in unexpected places. High-piled materials can lose the structural integrity of the pile, fall and spread fire or injure fire fighters. If not properly controlled with shutdown features, automated systems – such as robotics or carousels – can carry burning products far from where the fire originated.

To address these common yet complex fire challenges, the International Fire Code (IFC)™ devotes an entire chapter to fire prevention and protection strategies. Coupled with National Fire Protection Association (NFPA) fire detection and sprinkler standards, IFC Chapter 32 provides a comprehensive fire protection strategy for high-piled risk reduction and control.

Quantifying the Hazard

The foundation for protecting high-piled storage arrays begins with a clear understanding of the product(s) that will be stored. The items must be identified as “commodities” that include three essential elements: the product being stored, its packaging (if any) and the materials handling component on which it is placed (such as a pallet, rack or its own container). Each commodity’s relative combustibility – based on its measured or anticipated latent heat and heat release rate – must be classified to establish the appropriate protection level. This alone can be a daunting task given the nature of ever-changing product components, shipping and packaging practices and how commodities may be aggregated into a single load.

Unlike NFPA standards, the IFC requires commodities be identified into one of five groups: Class I through IV and high hazard. Table 1 summarizes the class requirements and provides examples of each.

The type and quantity of plastics in the product and packaging is particularly concerning because some plastics (and if they are rigid or foam) can have a significant influence on a commodities’ combustibility. Small changes in product packaging may have substantial consequences in the event of a fire. (The influence of plastics on commodity classification will be addressed in a subsequent article.)

Figure 2. Solid piles of boxed materials may fall in the event of a fire. Also, the space between boxes – called a flue space – is a perfect environment vertical for fire spread.

High-Piled Storage Configurations

The IFC addresses high-piled storage in a variety of configurations, each of which has its own fire behavior consequences:

  • Solid pile describes an array with materials closely packed in stacked piles, on shelves or in bin boxes where the containers and bin boxes are supporting one-another. (See Figure 2) In the event of a fire the material stack may collapse, endangering fire fighters and spreading the fire.
  • Bin boxes are five-sided containers – usually with an open top – that may be made from wood, cardboard, plastic or metal. They may be stacked and self-supporting or arranged in shelf storage or racks. Bin boxes may accumulate water from sprinkler systems and overload the structural stability of the array.
  • Shelf storage is storage on shelves less than 762 mm (30 inches) deep with a vertical distance between shelves not exceeding 914 mm (3 feet). Content laden shelves may prevent fire sprinkler discharge water from reaching burning materials.
  • Rack storage generally is any configuration larger than shelf storage. Typical warehouse rack storage units measure 2438 mm (8 feet) wide by 1219 mm (4 feet) deep to accommodate a pallet. Their height is limited only by the structural load and the ceiling clearance of a building. Rack storage fires often spread because fire sprinkler discharge cannot reach the heat source. Fires will spread vertically and horizontally.
  • Extra high rack arrays are Class I-IV materials on racks that exceed 12 192 mm (40 feet) or high hazard materials more than 9144 mm (30 feet).

Fire Protection Requirements

While automatic fire sprinkler protection is undeniably the best protection for stored goods, the IFC recognizes not all high-piled arrays create the same risk level. Other than ordinary housekeeping requirements, the IFC does not even regulate high-piled storage areas less than 500 sq. ft. ( m2).

For small storage areas, fire protection in the form of early detection coupled with methods to control smoke may provide a reasonable level of risk management to enable the local fire services to enter the storage area safely and suppress a fire. Consequently, the level of fire protection – based on commodity class – increases as the storage area increases.

Table 2 summarizes the fire protection options for small storage areas between 232 to 1115 m2 (2,501 and 12,000 sq. ft.). In this example, the property owner is given a choice of options: with or without automatic fire sprinkler protection. All high-piled storage areas more than 1115 m2 (12,000 sq. ft.) must be protected by a suitably designed automatic sprinkler system.

When an owner or operator chooses Option 1, an automatic sprinkler system designed in accordance with NFPA 13 and suitable for the commodity hazard classes is required. If Option 2 is selected, the storage area must be equipped with automatic fire detection (smoke detection is preferred but not required), additional perimeter access doors for the fire service to enter for rapid fire attack must be installed and the storage area must be equipped with automatic smoke and heat removal features such as rooftop heat vents or mechanical smoke control.

Figure 3. Plastic bin boxes on a rack storage array. When sprinklers discharge, the water may cool burning combustibles, but there is a risk of structural overload du to the accumulating weight.

Figure 3. Plastic bin boxes on a rack storage array. When sprinklers discharge, the water may cool burning combustibles, but there is a risk of structural overload du to the accumulating weight.

Classify with Caution

  • Extreme care must be used to properly classify commodities based on their potential fire hazard.
  • Review Class II commodities in Table 1 and you will see “foods in combustible containers” are categorized as a relatively low hazard product. A less experienced code official may accept that classification for all food products based on what he reads in the table.
  • However, take another look at the table for High Hazard commodities and you will find “vegetable oil and butter in plastic containers,” otherwise known as margarine. This product is essentially a hydrogenated combustible liquid stored in a combustible plastic container: one of the highest fire challenges that exist.
  • If you are uncertain about commodity classification, don’t hesitate to seek expert help.
Figure 4. Commodity classifications can be evaluated through fire tests such as this one performed by FM Global that measures heat release rate from a burning array.

Figure 4. Commodity classifications can be evaluated through fire tests such as this one performed by FM Global that measures heat release rate from a burning array.

Summary

High-piled storage facilities provide a complex variety of fire problems that often result in total building and contents losses. While built-in fire protection features are intended to mitigate the consequences of an unwanted fire, these features must be designed to match the hazard and maintained over time as commodities and storage methods change. New technology is creating a rapid evolution in the materials handling and storage industry, so fire professionals must stay informed and up-to-date to address the ever-changing risk.

The next issue will address the influence of plastics on commodity classification and fire protection.

For more information, go to codes.iccsafe.org

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Rob Neale is Vice President, National Fire Service Activities International Code Council.

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