Currently, the warehouse and distribution industries are faced with some major challenges that are impacting the typical way that business is being done. These challenges run the gamut from the continual changes in commodities and the introduction of new hazards to the continual evolution of sprinklers and the changes that have been proposed and are occurring in NFPA 13.1 There are so many changes impacting the warehouse field that the owner and many times the designer are trying to design to a moving target. The code official remains the gatekeeper; however, officials are also faced with the challenges of establishing design criteria and interpreting codes without sufficient information. This article will evaluate some of these issues and illustrate how the problems exist in today's warehouse and distribution environment.

Commodity Changes
In 1967, in the movie The Graduate, Benjamin Braddock (Dustin Hoffman) was told to get into plastics. Now, almost 40 years later, the warehouse industry has yet to fully come to grips with the continual influx of plastics. The problem is that the warehouse operator frequently doesn't see the change. To the warehouse operator, they are still selling hose reels for the home, which 25 years ago were metal and now are plastic. They are still carrying snow shovels, and the change to a plastic blade has not been recognized as an increase in hazard.


When a major fire occurs, such as the 1981 Kmart distribution warehouse fire,2 the fire protection industry addresses the issues and problems identified in the subsequent reports. Post-fire examination indicated a problem with aerosols breaching the fire walls, an improperly designed sprinkler system, and improperly segregated aerosols. As a result of this loss, NFPA 30B, Code for the Manufacture and Storage of Aerosol Products, was developed. Flammable liquids in small containers became an issue following the 1987 Sherwin-Williams fire.3 From this loss, a detailed series of fire tests evaluating the performance of flammable liquids in plastic containers was conducted and evaluated to outline the requirements that eventually appeared in NFPA 30, Flammable and Combustible Liquids Code. Yet, when a fire occurs in a warehouse that has had an evolution to a plastic commodity, the post-fire investigation report classifies the sprinkler system as being " underdesigned for the hazard," and there is no movement towards the development of major test procedures.


NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems4 places the responsibility for a properly designed system with the owner or occupant. The standard requires corrective action be taken when there is a change in the building parameters, including storage arrangement and commodity stored. Where changes are identified (which may occur during an inspection), the owner has the right to a second opinion to evaluate the level of protection provided by the sprinkler system. The owner is required to make any necessary corrections. The identification of these deficiencies can occur during an inspection of the sprinkler system which can be performed by the code official, the insuring agent, or even the sprinkler contractor.


Additional authority is provided in Section 1.4 of NFPA 13,5 which gives the authority having jurisdiction (AHJ) authority to retroactively modify any portions of the standard deemed appropriate where conditions present an unacceptable degree of risk.


Despite these requirements, commodity changes occur while the underdesigned systems remain. To solve this problem, there is a need for continual education of the owner. The authorities having jurisdiction or the other parties performing the inspections or evaluations must ensure the deficiencies and the reasoning behind these deficiencies are properly identified and explained.

The other problem that exists relative to commodity classification is that the examples given in NFPA 13, Annex A, although useful, have not kept up with technology. These examples do not provide current information such as: What would be the proper classification for compact discs or DVDs? How does one classify circuit boards or cell phones in boxes? The proper classification of a commodity is probably the most important decision made by the designer and yet the decision is based on "it seems like" rationalization.


Sprinkler Evolution
Twenty years ago, owners were faced with a limited sprinkler type selection decision. The sprinkler that was going to be installed was either a standard spray upright (SSU) or standard spray pendent (SSP). The temperature classification was determined by the ambient air temperature (although at times the temperature was changed due to design considerations), and the orifice size was either a standard orifice or a large orifice.


Even then, however, the writing was on the wall. The Early Suppression Fast Response (ESFR) sprinkler had been introduced into the standard in the 1989 edition. The large-drop sprinkler had been in the standard since 1985.


In the 1999 edition of NFPA 13, Section 5-4.1.2 (Section of the 2002 edition) was added. This section specifically addresses "general storage, rack storage, rubber tire storage, roll paper storage, and baled cotton storage" that are protected with a standard spray sprinkler (SSU or SSP). The section required a larger-orifice sprinkler for storage occupancies and even larger sprinklers for higher densities. If the design density is 13.9 mm/min (0.34 gpm/ft2) or less, a sprinkler with a nominal k factor of 8.0 or larger is required. If the design density is greater than 13.9 mm/min (0.34 gpm/ft2), a sprinkler with a nominal k factor of 11.2 or larger that is listed for storage applications is required.


The listing agencies started to list specialized sprinklers for storage applications only. The sprinkler approval standards needed to be revised to address specific testing for a listed storage sprinkler. The FM Approval Standard for Automatic Sprinklers (Series 2000)6 was the first to develop criteria for storage sprinklers. Section 4.38 of the FM Approval Standard outlines the requirements for the Extra Large Orifice, K11.2 sprinkler.


ESFR Sprinklers
Although fire control has long been the goal of NFPA 13 and is included in the test criteria, the concept of fire suppression was first introduced by the Early Suppression Fast Response (ESFR) sprinkler, which was developed to achieve suppression of a fire in a warehouse occupancy. When the former NFPA 231C Standard for Rack Storage of Materials was first developed, the standard clearly indicated that the intent of the sprinkler system was to achieve fire control. Appendix C (now known as Annex C in the 2002 edition of NFPA 13) defined the goals of the tests for storage heights over 7.6 m (25 feet) as:

  1. Determine the arrangement of inrack sprinklers that can be repeated as pile height increases and that provide control of the fire; and
  2. Determine other protective arrangements, such as high-expansion foam, that provided control of the fire.

Control was defined as holding the fire in check through the extinguishing system until the commodities initially involved are consumed or until the fire was extinguished by the extinguishing system or manual aid. Control was considered to be accomplished if the fire was unlikely to spread from the rack of origin to adjacent racks (did not jump the aisle) or spread beyond the length of the 7.7 m (25 ft) test rack. The sprinklers were not required to suppress the fire but were required to control the fire.


In the 2002 edition of NFPA 13, the same definition of fire control remains in Annex C, but a new definition for fire control appears in the body of the standard. Fire control is defined as "limiting the size of a fire by distribution of water so as to decrease the heat release rate and pre-wet adjacent combustibles, while controlling ceiling gas temperatures to avoid structural damage." At the same time that the definition for fire control was brought into the body of the standard, a definition for fire suppression was also added. Fire suppression was defined as "sharply reducing the heat release rate of a fire and preventing its regrowth by means of direct and sufficient application of water through the fire plume to the burning fuel surface."


The ESFR sprinkler is defined as a type of fast-response sprinkler that meets the fast-response criteria and is listed for its capability to provide fire suppression of specific high-challenge fire hazards. As a suppression-mode sprinkler, it reduced the need for inrack sprinklers. From the standpoint of the owner, anything that reduced (or eliminated) the need for in-rack sprinklers was a tremendous innovation that promised to revolutionize the warehouse industry. The sprinkler showed great potential in that not only were inrack sprinklers eliminated, the sprinkler also was a suppression-mode sprinkler and was designed to work with only 12 sprinklers flowing.


Due to the amount of water each sprinkler flows [(around 400 liters per minute (100 gpm)], its initial availability only as a pendent sprinkler, and the 0.9 m (3 ft) clearance requirement from the deflector to the top of storage, it quickly became evident that the ESFR was not a suitable retrofit sprinkler.


Perhaps the biggest issue was the obstruction requirements. The sprinkler was developed based on tests, and as such, the obstruction requirements were very specific and constraining. The 1989 edition of NFPA 13 (in which ESFR sprinklers first appeared) spoke of obstructions located below the sprinkler that were up to 300 mm (12 in) wide, whereas with the SSU and SSP sprinklers, the designer was only concerned about obstructions wider than 1.2 m (4 ft). From the beginning, the obstruction requirements were more severe than those used for the SSU and SSP sprinklers, and the requirements have evolved to become even more restrictive. As an example, currently any item, regardless of size, that is within a 0.3 m (1 ft) radius of the sprinkler and is within 0.6 m (2 ft) below the sprinkler is considered an obstruction. Obstructions include items such as conduit, bridging, cross-bracing, and piping.


For the first time, the sprinkler location and installation has to take precedence over other items in the building. Other trades are now required to coordinate with the sprinkler contractor as opposed to the more traditional other way around. The problem to the warehouse-operator that exists is that the new obstruction requirements are being enforced (quite often by the insurance company) on existing systems. What is potentially worse is that, if the owner is not aware of the threat imposed by that small piece of conduit (for example), they may allow a condition to be installed or remain in place that may result in a sprinkler system failure.


Solid Shelving in Racks
Perhaps the biggest change to impact the warehouse and distribution industries is found in the new solid shelving requirements for racking that appeared in the 2002 edition of NFPA 13. Figure 1 illustrates longitudinal and transverse flues. Prior to the 2002 edition, the sprinkler committee had defined solid shelving in a formal interpretation by stating that solid shelving occurs only when both the longitudinal and the transverse flue are blocked. The 1999 edition of the standard defined solid shelving as "solid, slatted, and other types of shelving located within racks that obstruct sprinkler water penetration down through the racks." The problem that frequently arose was the standard was not clear on where flues were required.


The flue space requirements that have been in the standard for years provide no further clarity into the problem. For storage up to and including 7.6 m (25 ft) in height, a longitudinal flue (back-to-back clearance between loads) is not required, while a nominal 150 mm (6 in) transverse flue space between loads and at rack uprights is required. When storage is over 7.6 m (25 ft) high, both a 150 mm (6 in) longitudinal and a nominal 150 mm (6 in) transverse flue are required (again, the transverse flue was required between loads and at rack uprights). The problem that arises is that a load has not been defined by the standard. Without direction in the standard, how does one identify a "load" of shoe boxes? Is a single shoe box placed on a rack intended to be a load, thereby necessitating a 150 mm (6 in) gap between boxes? Or would it be acceptable to pack these in tight and provide flues at the rack uprights, thereby defining the load as a single unit spanning between uprights?


Requirements found in certain sections of the 1999 edition of the standard gave the appearance of a conflict. ESFR sprinklers were not to be used on solid shelving, and yet if inrack sprinklers were to be installed, they were to be located at the intersection of the longitudinal and transverse flue space with a maximum horizontal spacing of 1.5 m (5 ft), thereby implying a flue every 1.5 m (5 ft) was required. Yet, slatted shelves (which are to be treated as solid shelving) were allowed to be protected with the k=11.2 sprinkler, if 75 mm (3 in) transverse flues were provided on 3 m (10 ft) centers. The authority having jurisdiction and the designer were left with interpreting the code due to the lack of clarity as it applied to flue spacing.


The NFPA 13 committee recognized the problem and attempted to deal with it in the 2002 edition of the standard. They specifically developed requirements for solid shelving in Section This section states that if the solid shelving exceeds 1.8 m2 (20 sq ft) but does not exceed 6.0 m2 (64 sq ft), sprinklers are to be installed below shelves at intermediate levels not more than 1.8 m (6 ft) apart vertically. If the solid shelving exceeds 6.0 m2 (64 sq ft) in area or where the levels of storage exceed 1.8 m (6 ft), sprinklers shall be installed beneath each level of shelving.


An issue that remains is that the definition of solid shelving states "and where the flue spaces are maintained"1 without outlining where these flue spaces should be provided. This relates back to the earlier issues regarding flue spaces at uprights and between loads.

It should be noted that the requirements for the protection of solid shelving make no distinction regarding storage height. Since Table applies to Commodity Class I through IV 3.7 m (12 ft) or Less in Height, some municipalities state that the requirements for solid shelving apply regardless of storage height.


The solid shelving issue also greatly impacts requirements in NFPA 13 that have been used for decades, thus bringing many existing warehouses into conflict with the standard. For years, the standard has stated that for storage up to 7.6 m (25 ft) in height, transverse flues only were required, and a longitudinal (back-to-back) flue was not required. Said another way, in a double-row racking arrangement, if the storage was up to 7.6 m (25 ft) high, a longitudinal flue was not required. Assuming the double-row rack constitutes two 1.2 m (4 ft) single-row racks back to back, the lack of the longitudinal flue would require one to measure the shelf from aisle to aisle and flue to flue. In order to compensate for the nonrequired longitudinal flue while still maintaining an area less than 1.8 m2 (20 sq ft) so as to not require inrack sprinklers, a transverse flue would need to be provided every 0.76 m (2-1/2 ft). The other design option would require in-rack sprinklers be provided every 1.8 m (6 ft) vertically. This is a major change to an item that has been in the standard for years (no longitudinal flue) and results in either providing a longitudinal flue or sprinklers being provided under each level or at 1.8 m (6 ft) intervals, depending on the actual calculated area.


The problem is compounded in multiple-row racks. Multiple-row racks are defined as "racks greater than 3.7 m (12 ft) wide, or single-or double-row racks separated by aisles less than 1 m (3.5 ft) wide having an overall width greater than 3.7 m (12 ft)." An example of a multiple-row rack would be a flow-through-type rack where loading is performed on one side and the material is allowed to flow through the racks by gravity to the other side for order fulfillment. The standard has never required a longitudinal flue space in these racks when storage is less than 7.6 m (25 ft) high. It also provided criteria for protection of these racks by the overhead sprinkler system only. The new solid shelf definition and resulting requirements will either require some type of intermediate stop be provided so that the loads do not abut each other or will require sprinklers below each level.


Building Code Impact
On top of all the challenges and changing requirements discussed above, the adoption of the International Building Code has significantly impacted the warehouse and distribution industry in certain parts of the country. In particular, owners and occupants in parts of the U.S. that were using the National Building Code (published by the Building Officials and Code Administrators, BOCA) have seen a major change in the warehouse and distribution industry. The 2003 International Building Code7 (IBC) in Section 910.2 requires smoke and heat vents be installed in any moderate-hazard storage occupancy (S-1) having more than 4,600 m2 (50,000 sq ft) in undivided area. If the building has high-piled combustible storage, smoke and heat vents are required by the International Fire Code8 in areas as small as 232 m2 (2,501 sq ft). This requirement for smoke and heat vents was not part of the National Building Code, but because it is part of the International Fire Code can be applied to existing buildings.


The IBC requires smoke and heat vents to be provided on a 0.09 m2 (1 sq ft) of vent area for every 7 m2 (75 sq ft) or 9 m2 (100 sq ft) of building area, depending on storage height. Since the IFC "establishes regulations affecting or relating to structures, processes, and premises, and safeguards from the hazard of fire and explosion...", it is intended to outline requirements for existing buildings. Both the Uniform Codes and the Standard Codes required smoke vents; it is only in those areas where the National Building Code had been adopted that the owner may find themselves in noncompliance.


Although the IBC does have an exception that vents are not required when ESFR sprinklers are provided, NFPA 13 states in Section 12.1.1 that "sprinkler protection criteria are based on the assumption that roof vents and draft curtains are not being used."1 Again it appears that the owner may be faced with conflicting opinions regarding the need for and effectiveness of smoke and heat vents in a sprinklered building.


Gerald R. Schultz is with the Fire Protection International Consortium, Inc.



  1. NFPA 13, Standard for the Installation of Sprinkler Systems, 2002 edition, National Fire Protection Association, Quincy, MA, 2002.
  2. NFPA Fire Investigations Report, "Storage Fire (Kmart), Fall Township, PA, June 21, 1982," National Fire Protection Association, Quincy, MA.
  3. NFPA Fire Investigations Report, "Flammable Liquid Warehouse Fire, Dayton, Ohio, May 27, 1987," National Fire Protection Association, Quincy, MA.
  4. NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, 2002 edition, National Fire Protection Association, 2002.
  5. NFPA 13, Standard for the Installation of Sprinkler Systems, 2002 edition, National Fire Protection Association, Quincy, MA, 2002.
  6. FM 2000, Approval Standard for Automatic Sprinklers (Series 2000), Factory Mutual Insurance Company.
  7. International Building Code, 2003 edition, International Code Council, 2003.
  8. International Fire Code, 2003 edition, International Code Council, 2003.