There is more than meets the eye when it comes to sprinkler protection in storage areas. Rooms labeled “storage” can be as innocuous as a small coat closet or janitor’s closet, or it can be as daunting as a warehouse full of highly flammable materials. The National Fire Protection Association (NFPA) provides ample amounts of guidance on how to protect indoor storage areas in NFPA 13 (2022 edition), Standard for the Installation of Sprinkler Systems. 

However, this guidance is spread out throughout multiple sections and chapters and involves dozens of different tables and charts. Without a plan of attack, deciphering these sections and coming to a design for your storage area can be an intimidating task. This column aims to begin to demystify the process of sprinkler design for storage areas by providing an intuitive, streamlined approach.

Let’s begin with the obvious starting point. 

Product classification

To provide a sprinkler design for your storage area, we first need to analyze exactly what is being stored: empty glass jars, for example, will carry along a vastly different fire risk than Styrofoam cups and, thus, should be treated differently. 

Sections 20.3 and 20.4 of NFPA 13 provide guidelines on classifying different materials being stored. This chapter divides the classification of commodities into nonplastics and plastics. Nonplastic commodities are classified on a scale from Class I to Class IV, with Class IV providing the highest fire risk. 

Plastic commodities are divided into Group A, Group B and Group C plastics, with Group A plastics providing the highest risk. NFPA 13 considers the fire risk for Group B plastics and Class IV commodities to be equivalent; the same goes for Group C plastics and Class III commodities. 

Thus, a ranking of commodity classifications is as follows:

To complicate the issue even more, NFPA 13 also divides Group A plastics into four subcategories: cartoned or exposed, expanded or nonexpanded. A cartoned plastic is one where a corrugated cardboard or paperboard container fully encloses the commodity, whereas an exposed plastic is not. 

An expanded plastic has numerous small cavities dispersed throughout its mass. For example, bubble wrap is considered an expanded plastic because it has air-filled pockets throughout, whereas PVC would be considered a nonexpanded plastic because it is solid throughout its mass. 

Due to the pockets of air throughout its mass, expanded plastics are considered to have a higher fire risk than nonexpanded plastics, as the pockets of air facilitate a quicker and more efficient mixture of fuel and air that grows an ongoing fire. As such, a more in-depth ranking of commodity classifications is as follows:

It is important to note that the stored commodity is not the only contributor to its classification. To best illustrate this, let’s consider an example where glass jars filled with noncombustible liquids are being stored. Our first thought might be that glass is not combustible, so we can classify this as a Class I commodity based on the definitions provided in Section 20.4.1 of NFPA 13. 

We can additionally check the annex of NFPA 13 (Table A.20.4(b)), which provides a long list of common commodities and their commodity classification. And we would find that our product is a Class I commodity. 

Easy enough? Not so fast; let’s look a little bit closer. 

We may then look at Section 20.4.2, which states that noncombustible products stored in solid wood boxes would be considered a Class II commodity, even though the commodity itself remains noncombustible. We may also look at Section 20.3.2.2.1 or 20.3.2.2.2, which states that the commodity classification ranking can be increased by one or two classes depending on what kind of pallet it may be stored on. 

In a worst-case scenario, our noncombustible glass jars, when stored in solid wood boxes and upon a reinforced plastic pallet, now become a much more onerous Class IV commodity. This example, while contrived, illustrates the importance of knowing all the information about the product you are storing — it’s not only the product, but all the bells and whistles that come with it.

Storage height

Now that we know how to classify the commodity we are storing, we can determine what part of NFPA 13 sets its design criteria. NFPA 13 provides definitions for low-piled storage, high-piled storage and miscellaneous storage. Low-piled storage is defined as the storage of Class I through Class IV commodities stored up to 12 feet in height, or Group A plastic commodities stored up to 5 feet. 

The definition for miscellaneous storage is slightly more nuanced as detailed in Section 4.3.1.4 of NFPA 13. It is considered a storage area meeting all the following requirements: the individual storage area is not greater than 1,000 square feet, the total amount of storage area does not exceed 4,000 square feet or 10% of the building area (whichever is greater), individual storage areas do not exceed 12 feet in height, and the individual storage areas are separated by at least 25 feet from each other. 

For example, consider a warehouse with 20,000 square feet of a Class III commodity stored at a height of 10 feet; this would be an example of low-piled storage. An industrial facility might have three different shelving areas of the same Class III commodity, all 800 square feet, all stored at 10 feet, and all separated by 30 feet; this would be an example of miscellaneous storage. The difference is nuanced but important. 

Lastly, high-piled storage would be the storage of Class I through Class IV commodities at a height greater than 12 feet, or the storage of Group A plastics at a height greater than 5 feet. For the protection of low-piled storage and miscellaneous storage, we will stay in Chapter 4 of NFPA 13 for guidance. For the protection of high-piled storage, we will look to Chapters 21 through 27 of NFPA 13.

Storage methods

The last thing we need to establish is the different methods of storing commodities. NFPA 13 defines the following storage orientations: solid-piled, bin-box, palletized, shelf, single-row rack, double-row rack, multiple-row rack and back-to-back shelf storage. 

The definitions for these methods of storage can all be found in Chapter 3 of NFPA 13. 

At first glance, their differences may seem slight. However, because of the way different storage methods might block water from reaching combustibles, allow for oxygen to travel through small gaps in the storage and contribute to the fast growth of fire in a storage occupancy, each storage method might be protected differently even when considering the same commodity, stacked at the same height, in the same room.

Sprinkler design criteria

At long last, we are now ready to determine our sprinkler design criteria for low-piled and miscellaneous storage (the protection of high-piled storage has even more information to establish, which will be detailed in a future column). 

Table 4.3.1.7.1.1 displays the discharge criteria required for low-piled and miscellaneous storage. Based on the commodity classification, the method of storing the commodity, the maximum storage height of the material and the maximum ceiling height, this table will give you the corresponding hazard classification, details on in-rack sprinklers (where required) and hose stream allowances required to protect the commodity. It’s really that simple!

Let’s run through a couple of examples to illustrate the process from start to finish. In Example 1, consider a situation where we store a mixture of commodities: 90% by weight is cartoned cotton and 10% by weight is synthetic fabric. The material is stored in bin-box storage at a height of 11 feet and the room it is stored in has a ceiling height of 15 feet. 

First, we will go to Table A.20.4(b) and find that cartoned cotton is a Class III commodity, whereas synthetic fabric is a Group A nonexpanded plastic. No need to worry that we have two different commodity classes in the same area, partly thanks to Figure 20.4.3.3(a) in NFPA 13. This figure sets guidelines for classifying mixed commodities based on the percentage of Class III commodities, Group A expanded plastics and Group A nonexpanded plastics. 

In our situation, as illustrated in Figure 4, our mixture of commodities would be considered a Class IV commodity. 

A Class IV commodity stored at 11 feet is considered low-piled storage, so we can reference Table 4.3.1.7.1.1 for the sprinkler design criteria required to protect it. And, considering the commodity is stored in bin-box storage, the table tells us we would protect this area with an Ordinary Hazard Group II sprinkler system. 

In Example 2, consider a situation where Styrofoam (polystyrene) is stored on single-row racks at a height of 10 feet with a ceiling height of 30 feet. Again, we will go to Table A.20.4(b) to find that polystyrene products are considered a Group A expanded plastic. Based on our definitions in Chapter 3, a Group A plastic stored higher than 5 feet is considered to be high-piled storage, not low-piled storage. We can no longer rely on Table 4.3.1.7.1.1. 

As previously mentioned, the requirements for high-piled storage involve even more nuance and will be covered in a future column. 

I hope it is clear that the sprinkler protection of storage areas is a complicated and detailed subject deserving close attention. It is easy to let details slip through the cracks, leading to improper coverage of an incredibly high-risk fire load in a building. 

However, with fine attention to detail, the Herculean task of protecting storage occupancy can be broken down into smaller and simpler tasks. Following the blueprint that has been explained will lead to the adequate protection of low-piled and miscellaneous storage in a building and set the foundation for the protection of high-piled storage.

 Jack DeVine, PE, is a fire engineer at Arup based in Boston. He has an extensive background in designing fire sprinkler systems for various types of commercial buildings, as well as a broad foundation in fire/life safety code consulting and performance-based design. DeVine has a master’s degree in fire protection engineering from Worcester Polytechnic Institute, where he has since guest-lectured in human behavior in fire, fire modeling and evacuation modeling.