One of the most challenging occupancies requiring fire sprinkler protection is storage in many configurations. Good familiarity with the building and fire codes, along with the 2022 edition of NFPA 13, Standard for the Installation of Sprinkler Systems, is essential to the layout and installation of such systems. 

Other codes or standards may be acceptable to the authority having jurisdiction over such a property. An example might include the design criteria developed by commercial property insurance firm FM Global for such occupancies.

No matter which guidelines are to be followed, the following variables will impact the final approach to sprinkler protection (in no particular order).

What Is Being Stored? 

This is often referred to as a commodity class, which provides a guideline as to the potential fire hazard represented by the product. The classes range from I to IV; additionally, several groups of plastics represent, by their very nature, a greater challenge to control a potential fire condition. 

Some examples include, but are not limited to:

• Class I: metal desks, gypsum board, water-based paint in metal containers, electric motors, liquids in glass bottles or jars, bare wire on metal spools. 

• Class II: bare wire on wood or cardboard spools, lumber or plywood in bundles, pharmaceuticals in glass bottles, empty wood containers, shock absorbers with a metal dust cover, wire with PVC insulation on metal or wood spools.

• Class III: frozen foods in plastic trays, bagged charcoal, roofing shingles, clothing of natural fibers, tobacco products in cartons.

• Class IV: empty plastic bottles or jars, small arms ammunition, pharmaceuticals in plastic bottles or jars, synthetic cloth, nylon and rayon fabric.

• Group A plastics: vehicle batteries of any size, milk with containers stored in plastic crates, furniture and bedding with foam cushioning, carpet tiles in cartons, stuffed toys, candles, bare wire on plastic spools.

As you can see, a product may be designated as a different commodity class under certain conditions, depending on how it is packaged. For example, pharmaceuticals in a glass jar is a Class II. If the container were plastic, the commodity would increase to Class IV.

Additional consideration should be given to the commodity classification in the appropriate adopted building or fire code. There are some instances where the codes determine a commodity class that does not agree with NFPA 13. If the fire or building code classification is greater than that from the standard, the greater of the two should be applied. 

How Is It Being Stored?

This consideration spans a range of criteria. Storage may be stacked on the floor, on pallets on the floor, on shelves, on back-to-back shelves or in storage racks. Another consideration would be how the storage is contained, whether in cartons or exposed. When plastic protection is under consideration, the latter becomes more important.

Among the potential issues to be considered are the aisle configurations for either rack or floor storage. Planned and maintained aisle widths can significantly impact the eventual criteria to protect storage. 

How High Is the Planned Storage?

NFPA 13 has established dividing lines for storage protection in various heights above the finished floor. The top of storage is designated as above or below this height when establishing protection methods.

An awareness of the intended height of the top of the storage can be crucial to developing the layout criteria for a fire sprinkler system. In short, the higher the storage, the more demanding the sprinkler system criteria. 

Two additional concerns regarding height address the sprinkler deflector itself. The first is the minimum clearance from the top of the storage to the deflector; the second is the required position of the deflector relative to the deck, ceiling and framing members above. 

How High Is the Ceiling Above the Storage?

As in most cases where the sprinklers protecting such storage occupancies are located close to the ceiling, an understanding of the distance between the sprinkler and the top of the storage can significantly impact the resulting protection criteria. 

All the criteria in NFPA 13 are quite specific about water delivery to address a potential fire. In many of those, the mandate is for a certain quantity of water to be delivered over a specified area. This is expressed as gallons per minute per square foot required over a hydraulically remote area. This approach is referred to as the area/density method.

However, another type of sprinkler is currently available which omits consideration of the density (quantity of water per square foot) and relies solely on the provision of a specific amount of pressure — expressed in pounds per square inch — resulting in a very specific minimum quantity of water from each sprinkler. Such sprinklers are classified as early suppression fast response (ESFR). 

ESFR sprinklers have undergone extensive testing to support their use in addressing storage fire protection, and while there are limitations on where/when they can be used, their use has become quite common.

Among the limitations:

• ESFR sprinklers are not permitted to protect storage on racks with solid shelves unless sprinklers are also installed in the racks.

• ESFR sprinklers are not permitted to protect storage in open-top containers.

• The maximum distance from an adjacent wall cannot exceed 12 feet when the ceiling height in the storage area is up to 30 feet; this is reduced to 10 feet when the ceiling height is more than 30 feet in height.

The hydraulic calculations performed to support the pipe sizing for either the area/density or ESFR approach to storage fire protection must be evaluated for the ability of the available water supply to meet the demands. 

Water Supply

One other consideration has to do with the water supply. The information should be as current as possible. Indeed, NFPA identifies that whenever actual physical flow testing has been performed, the results must be no more than 12 months old. However, many water purveyors do not perform or allow physical testing of the water supply, relying instead on computer simulations to develop the values.

The development of a storage protection method can be limited by the available water supply, expressed in both gallons and pressure. Indeed, some of the methods previously discussed, such as the ESFR sprinkler, deal almost exclusively with the pressure required for operating sprinklers. This can result in such methods being impractical.

Additional considerations in storage protection include (but are not limited to) aisle widths, exit travel distances, fire alarm and detection systems, portable fire extinguishers, smoke and heat vents, dead ends, and the required housekeeping. Often, the criteria for these items and the minimum/maximum to be applied are found in the building or fire code. 

The fire protection system design criteria for storage must consider a substantial number of variables. Modifications to existing systems or the development of new systems to meet those challenges should not be commenced without a thorough understanding of how that information can impact the eventual layout and installation.

Kenneth W. Wagoner, SET, is the owner of Parsley Consulting, located in Harrisonville, Missouri. He has more than 43 years of experience in automatic sprinkler systems and fire alarm system design, plan review, and construction management. Wagoner has presented classes through the auspices of the American Fire Sprinkler Association and the San Diego Fire Protection Association. Contact him at 760-745-6181, www.parsleyconsulting.com.