Fire Sprinkler Safety In Warehousing and Pallet Racking

Posted by Damian Mattey on April 6, 2022
( Last updated on 14 July, 2022 )
Damian Mattey
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A warehouse fire is not as uncommon as you might think. According to the National Fire Protection Association (NFPA), an average of 1410 warehouse fires a year were reported in the United States between 2014-2018 which equates to about 3-4 warehouse fires a day. This means while you are reading this, a warehouse is dealing with a fire that has the potential to cause warehouse damages, injuries, and even loss of life.

Leading Causes of Warehouse Fires

Leading Causes of Warehouse Fires
Figure 1. Leading causes of warehouse fires (2014-2018).

The Invention of Fire Sprinklers

Thanks to the invention of sprinkler systems, most warehouse fires are put out safely. Sprinklers have become one of the most effective ways in reducing the potential for damage and loss of life in a warehouse fire. Luckily the NFPA provides codes and standards which are used in over 50 countries, including the USA and Canada, to help facilitate the proper use of sprinklers. When you think about fire safety, it’s important to consider how your racking configuration can also impact the different factors required in implementing an adequate sprinkler system.

How Do Fire Sprinklers Work?

Sprinklers work the same way as a faucet does in your home, the difference being that heat is what causes the water from the sprinkler to flow. A sprinkler consists of a heat-sensitive glass bulb that is filled with a glycerin-based liquid that expands when heated. The glass bulb is designed to shatter the moment it reaches a specified temperature. Once the glass bulb is shattered, the plug is then released, and the water begins to pour down onto the deflector. Directly beneath every sprinkler, you will see a flower-shaped piece of metal called a deflector. The deflector distributes the water in a specific pattern based on the direction the water needs to be dispersed.

Fire Sprinkler head photo and parts diagram

Figure 2. Sprinkler photo and diagram.

Warehouse Storage Commodity Classification

The first step in figuring out your sprinkler design for your warehouse is by determining the commodity classification of what is being stored. Commodities can be classified between Class I-IV or Plastics A, B, or C. The reason plastics have a separate classification is due to the high temperatures and speeds at which they burn. Classifying a commodity incorrectly is a very expensive mistake that can lead to an ineffective sprinkler system that will not be able to control a fire.

The following questions are an important starting point in understanding your commodity classification:

  • What materials or chemicals are the stored products made of?
  • What type of packaging/container will the products be placed in?
  • Will the products be wrapped in plastic?
  • What type of pallet is being used (wood or plastic)?

5 Strategies to Improve Rack Safety Recorded Webinar

In Rack Fire Sprinkler Design and Limitations

When integrating a sprinkler system into your racking, there are several factors to consider. The main types of sprinkler systems you will most commonly see in a warehouse are ceiling sprinklers and in-rack sprinklers. In some cases, only using ceiling sprinklers will suffice due to their larger orifice which releases much bigger water droplets to penetrate fire deeper than traditional sprinklers. However, ceiling sprinklers will have to be combined with in-rack sprinklers if flue space requirements are not met.

In-rack fire sprinkler system (pallet rack)
Figure 3. In-rack fire sprinkler system
Ceiling sprinkler
Figure 4. Ceiling fire sprinkler system

Warehouse Fire Sprinkler Design for Flue Space

The NFPA defines flue space as clear vertical openings from the floor up to the ceiling within rack storage areas. Flue spaces are vital in the field of fire protection since it allows the heat to ventilate upward and activate a ceiling sprinkler system much quicker while also allowing water to penetrate down throughout the racking system. Not having sufficient flue space can increase the chances of your fire growing horizontally, placing your entire racking system and everything stored on it directly in the line of fire.

There are two types of flue spaces:

  1. Transverse: The space between pallets and between pallets and uprights within each row that run parallel to the loading direction.
  2. Longitudinal: The space between rows of racks.
Pallet Rack Flue space
Figure 5. Flue space

Depending on your specific Authority Having Jurisdiction (AHJ), you will be required to follow specific flue space requirements as building codes vary from place to place. Ideally, flue spaces should be approximately 6 inches wide depending on the storage height and the type of racking configuration. To learn more about appropriate clearances, refer to our blog related to recommended clearances in warehouses.

When Are In-Rack Sprinklers Required?

The need for in-rack fire sprinklers comes when the water penetration from the ceiling sprinklers is impeded from getting to the fire anywhere in the system. One solution to consider is to change any solid shelving you might have in your warehouse with wire decking to allow ceiling sprinklers to reach lower levels.

Waterfall wire decking
Figure 6. Waterfall wire decking

The following factors will determine if you need an in-rack sprinkler system:

  1. Types of commodity classification throughout your warehouse
  2. Storage and ceiling height of your warehouse
  3. Width and location of flue spaces in your racking configuration
  4. Presence of solid shelves
  5. Having an adequate water supply

The effectiveness of the fire protection system may be affected if your warehouse has had changes affecting these factors. The responsibility falls on the building owner to identify where these changes have occurred and inform a fire safety professional so that the fire protection system can be reevaluated.

Considerations and Requirements For In-Rack Fire Sprinklers

Sprinkler design requirements come from a robust set of fire test data that has set the standard of how we should be positioning in-rack sprinklers. Here are a couple of tips to position them properly:

  • Make sure to arrange the in-rack sprinkler and piping in a way that is safe from any mechanical damage caused by a potential forklift accident. While making sure that the sprinklers are protected it is still vital that the sprinklers are in a location in which the water can be discharged as intended. To learn more about common forklift accidents in the warehouse, read this.
  • Wherever in-rack sprinklers are needed, ensure that the deflector is positioned at or just below the bottom of a horizontal brace member.
  • Avoid placing sprinkler heads directly behind rack uprights and ensure no more than a 3-inch horizontal offset from the transverse flue space.

Seismic Considerations for In-Rack Fire Sprinkler Systems

If located in a seismic region, make sure to have sufficient clearance and protection from the piping and racking components to prevent any damage caused by a seismic event. To ensure the lifespan of a sprinkler system, is it important to follow proper seismic design guidance using the most recent edition of NFPA 13.

Seismic Related Clearances for Fire Sprinklers

NFPA 13 details the exact clearances needed depending on the nominal diameter of the piping used:

  • If the diameter of the pipe is between 1 and 3.5 inches, then clearance of 2 inches must be provided.
  • If the diameter of a pipe is 4 inches or larger, a clearance of 4 inches is required.

Are Warehouse Fire Sprinklers Worth the Trouble?

Fire protection can make a significant difference in the safety of your building and the people in it if you follow the regulations and requirements that apply to your specific region. Some might believe that following these guidelines could cost more money or be too difficult for them to keep up with, but it’s simply not worth gambling with the lives of all those who work inside your facility. According to the NFPA, sprinklers should be inspected annually from the floor level.

Therefore, as a responsible business owner, there are certain safety protocols that you should never overlook. You can start by having your racks assessed by an engineer at Damotech, who can identify if your rack configuration is causing any fire protection issues while also providing the necessary solutions to ensure compliance with regulations and standards by the appropriate authority having jurisdiction. Also, our Damotech engineered rack repair kits provide a seamless and cheaper alternative to replacing damaged racks because there is no need to reposition or dismantle your in-rack sprinkler system.


NFPA, (2020) Warehouse Fire Safety Fact Sheet. Retrieved from
FM Global. (2020). "Storage of Class 1, 2, 3, 4 and plastic commodities”. Retrieved from
NFPA 13 (2019), Standard for the Installation of Sprinkler Systems (2019). Retrieved from
Sprinkler Age, (2016) “How to Determine Commodity Classification.” Retrieved from
Allianz Risk Consulting (2019), “Why Rack Flue Spaces are Important” Retrieved from
Industrial Pallet Rack & Equipment Inc, (2021) “Pallet Rack Shelving Options” Retrieved from
Triangle Fire Systems, (2021) “Fire Sprinkler heads” Retrieved from

Topics: Pallet Racks, Blog, Material Handling Industry, Sprinklers, Fire Safety