Of Stores, Storage and Sprinkling

By Lisa Bossert, P.E. Fire Protection Engineer, Schirmer Engineering, Charlotte, N.C. February 1, 2006

Many big box retailers stack their merchandise to the ceiling. If heights exceed 12 ft.—on racks or in piles—these buildings are subject to many of the same fire protection requirements as warehouses. Certain high-hazard products such as rubber tires, Group A plastics, flammable liquids and idle pallets may be considered high-piled if their height exceeds 6 ft. Most building codes reference a high-piled storage chapter in their respective fire code. Requirements may include enhanced fire suppression, fire detection, smoke/heat removal systems, draft curtains, hose connections and fire department access as well as limitations on the dimensions of piles and aisles. Typical requirements are included in the International Fire Code (IFC), Chapter 23 (2000 or 2003 edition).

The first step in evaluating fire protection requirements is to classify the commodity. Product packaging must be considered since it may contribute to the hazard. (See “Commodity Classifications” and “Important Retail Storage Terms” below). Consult NFPA 13 for complete definitions and examples.

Sprinkler requirements

The presence of high-piled storage will often mandate a code requirement for fire sprinkler protection that otherwise would not be required. For example, the IBC requires mercantile occupancies to include sprinkler protection when the area exceeds 12,000 sq. ft. It also mandates compliance with Chapter 23 of the IFC when the merchandise is high-piled or rack-stored. Table 2306.2 of the IFC requires sprinkler protection when an area exceeds 500 sq. ft. for high-hazard commodities, and 2,500 sq. ft. for commodity Classes I—IV.

Note that Table 2306.2 includes separate requirements for public and nonpublic accessible areas of sizes 501 to 12,000 sq. ft. Sprinkler protection is mandated for public-accessible areas, but a non-sprinklered option is allowed for nonpublic-accessible areas. Beyond 12,000 sq. ft., the table does not differentiate between public and nonpublic accessibility. Thus, the fire protection requirements for high-piled or rack-storage areas beyond 12,000 sq. ft. are the same for big box retailers as they are for warehouses of the same size. Where required by Chapter 23, sprinkler protection must be provided throughout the building or to fire resistance-rated barrier walls.

Chapter 23 indicates whether or not a sprinkler system is required, but it does not include the design parameters. The designer must consult NFPA 13, specifically Chapter 12 (2002 edition). Chapter 12 is difficult to navigate because it is comprised of 65 pages of text, tables and figures that pertain to palletized, rack and miscellaneous storage configurations of various commodity classifications. Fortunately, the proposed 2007 edition of NFPA 13 will divide Chapter 12 into nine separate chapters.

Section 12.2 pertains to palletized, solid-piled, bin box or shelf storage. Section 12.3 pertains to rack storage. Subsections exist for commodity classification, storage heights and sprinkler technology including Class I—IV up to 25 ft. (12.3.2), plastics up to 25 ft. (12.3.3), Class I—IV over 25 ft. (12.3.4) and plastics over 25 ft. (12.3.5). Each of these subsections is then subdivided for the various sprinkler technologies: control-mode, large drop, early-suppression fast-response (ESFR), rack or special sprinklers.

The design parameters for conventional sprinkler systems may vary significantly based on any of the following factors: commodity classification, encapsulation, rack type, aisle width, storage height and sprinkler temperature rating. However, the design parameters for ESFR systems are the same for many types and configurations of storage. Given the storage flexibility offered by ESFR technology, these sprinklers are especially valuable to retailers who offer a wide variety of products or to building owners who may have tenant turnover. The use of ESFR systems also allows storage of idle pallets to the same heights as the main products, whereas conventional sprinkler systems would limit the storage of idle pallets.

Additional advantages of ESFR systems include the elimination of rack sprinklers, smoke-removal systems and draft curtains that would otherwise be required if conventional sprinklers were used. Omission of rack sprinklers and all their design parameters, however, is contingent on there being no solid shelving present.

The performance of ESFR systems requires that high rates of water be applied directly, at high volume and high momentum, without delay to burning commodities. As such, ESFR systems must be wet—no dry or preaction systems allowed—and they have strict obstruction criteria. Structural framing must be coordinated with sprinkler placement, and certain types of construction are not compatible with ESFR. Additionally, there are detailed requirements to avoid obstructions below the elevation of the ESFR sprinklers that will affect placement of ductwork, lighting, cable trays, grouped conduit, pipe, etc. ESFR systems must be installed with strict adherence to NFPA and manufacturer criteria.

Available ESFRs are referred to as K14, K17 or K25—values representative of their orifice size. K14 ESFRs were the first type available and require the highest pressures. K25s are the most recent advancement and require the least pressure. However, designer selection should consider that an individual K25 sprinkler currently costs approximately $10 more than a K14. In many cases, the additional cost of K25s may be worthwhile. For example, the lower pressure requirement of the K25s may eliminate the need for a fire pump that would otherwise be required by K14 ESFRs. Beyond a comparison of initial installation costs, K25s may be selected since they are the only ESFR listed for the protection of 40-ft. rack storage in a 45-ft. building without supplemental rack sprinklers; for these heights, the use of K14 and K17 ESFRs requires one level of rack-sprinkler protection.

Smoke-removal systems

In addition to enhanced fire sprinkler requirements, the presence of high-piled storage may mandate smoke/heat-removal systems. (See the IFC, Table 2306.2). Methods include smoke/heat vents or mechanical smoke-exhaust systems and draft curtains designed per Section 910. These requirements were originally mandated by code to confine and release heat from buildings to reduce structural damage and to improve conditions for firefighters.

While smoke/heat vents and draft curtains may provide value in non-sprinklered buildings, their presence in sprinklered buildings has long been an issue of debate. Opponents state that sprinkler systems will cool smoke such that it does not need to be vented. Beyond being unnecessary, opponents say the presence of vents and draft curtains is actually detrimental to the performance of sprinkler systems. Hundreds of tests have demonstrated that vents and draft curtains direct heat away from the fire, causing remote sprinklers to operate, which deprives those sprinklers directly over the fire of water, decreasing their effectiveness. Draft curtains are actually prohibited from being installed within the boundaries of ESFR systems, as is addressed in the ESFR sprinkler section.

The codes recognize that the quantity of smoke produced is a direct effect of the ability of fire sprinkler systems to detect and control fire. Acknowledging the superior technology of ESFR systems, the 2003 IFC does not require smoke/heat-removal systems and draft curtains if the building is protected with ESFR sprinklers (IFC, 2003 edition, Table 2306.2, footnote j). Draft curtains are required, however, at the separation between ESFR sprinklers and conventional sprinklers (IFC, 2003 edition, 910.3.4 Exception).

As an alternative to vents, many building owners, designers and authorities prefer mechanical smoke-exhaust systems. They are considered preferable since the fire department can elect to operate exhaust fans based on its assessment of the fire emergency. Requirements for mechanical smoke-removal systems include:

Means of supply air, sized to provide a minimum of 50% of the exhaust capacity. Supply air is typically provided via interlocked louvers at or near the floor level, uniformly spaced around the area served.

The control panel should be located to be immediately accessible to the fire department from the exterior of the building. The location shall be within an area having a minimum 1-hr. fire-resistance rating.

Interlocks must shut down comfort air-handling systems so that airflows don’t interfere.

Wiring to the fans and to the associated control panel must be connected prior to the building’s main power disconnect. The wiring must be protected against physical and thermal damage, either installed on the outside of the building or rated to withstand more than 1,000°F for a minimum of 15 minutes.

In lieu of prescriptive design parameters for exhaust capacity, a performance-based design may be implemented for mechanical smoke removal systems. Based on the specific fire hazard, building geometry and fire-suppression system characteristics, a unique fire size can be determined using computerized fire simulations. The resultant fire size can then be applied to the equations used for smoke-control systems (Section 909) to determine an exhaust rate. Although a mechanical smoke-removal system for a high-piled storage area is not subject to the same life-safety objectives as a smoke-control system typically used in an atrium, the principles of fire dynamics remain the same. The system must be substantiated as an alternate method, and authorities typically require that a fire protection engineer prepare the analysis.

Thinking inside the box

Big box retailers often require fire protection similar to storage warehouses. Enhanced fire sprinkler protection and smoke removal systems may be required. ESFR sprinklers offer superior performance that allow product versatility and may eliminate or reduce requirements for rack sprinklers, smoke-removal systems and draft curtains.

Key Retail Storage Terms

Important terms in big box fire protection are encapsulation, rack type, flue spaces and solid shelving.

Encapsulation is the packaging method of shrink-wrapping the sides and top of pallet loads. Its presence contributes to the fire hazard because sprinkler water is unable to soak the packaging material to delay or prevent its ignition. Banding—shrink-wrap around the sides only—is not considered encapsulation. This method affects design parameters for conventional sprinkler systems but is inconsequential for ESFRs.

Racks. Single-row racks have a width up to 6 ft.., with aisles a minimum of 3.5 ft. from other storage. Double-row racks are two single-row racks placed back-to-back; the combined width is up to 12 ft., and aisles must be a minimum of 3.5 ft. from other storage. Multiple-row racks have a width greater than 12 ft. and include single- or double-row racks separated by aisles less than 3.5 ft.

For conventional sprinkler systems, the requirements are the same for single- and double-row racks, whereas multiple-row racks have more stringent parameters. Requirements for ESFR systems, however, are the same for all rack types.

Flue spaces. These spaces are important because they allow sprinkler water to soak products on lower levels. Obstructed flue spaces may reduce the effectiveness of sprinklers and possibly contribute to a fire growing beyond control. Transverse flue space is defined as the space between rows of storage parallel to the direction of loading. Longitudinal flue space is defined as the space between rows of storage perpendicular to the direction of loading. For storage up to and including 25 ft., no longitudinal flue space is required, but a 6-in. transverse flue space is required. For storage over 25 ft., 6-in. flue spaces are required in both directions.

Solid shelving. Just as open flue spaces are required to allow sprinkler water to reach lower levels, there can be no solid shelving. If the area of continuous solid shelving is more than 20 sq. ft., rack sprinkler protection is required, according to NFPA 13, 2002 ed., Section If the solid shelving area is 20 to 64 sq. ft., rack sprinklers must be installed at vertical distances not to exceed 6 ft. Where solid shelving exceeds 64 sq. ft., rack sprinklers must be installed beneath each level of shelving. Note that NFPA does not consider solid shelving to include slatted or wire mesh more than 50% open.

Commodity Classifications

Class I: noncombustible products in single-layer corrugated cartons, with or without wooden pallets.

Class II: noncombustible products in slatted wooden crates, solid wood boxes or multi-layer corrugated cartons, with or without wooden pallets.

Class III: combustible products—i.e, wood, paper, natural fibers or Group C plastics—with or without cartons, boxes or crates and with or without wooden pallets. May contain a limited amount—5% or less by weight or volume—of Group A or B plastics. Level 1 aerosols are also included.

Class IV: Class I, II or III products that contain an appreciable amount of Group A plastics—5% to 15% by weight or 5% to 25% by volume—with or without wooden pallets. May contain Group B plastics or free-flowing Group A plastics. Level 2 aerosols are also included.

Plastics: Groups A—most severe; B or C—least severe. See NFPA for specific list of materials. Plastics are further classified as expanded or unexpanded. Expanded plastics are styrofoam-like and are more hazardous than unexpanded plastics.

High hazards: Consult the local fire code for specific examples, including flammable/combustible liquids, aerosols, rubber tires, etc. There are numerous NFPA codes for the protection of specific product hazards and processes.

See the IFC 2000 or 2003 edition, Section 2302 for definitions and examples of Class I—IV and High Hazard Commodities.