Fire Sprinkler Safety Requirements in Warehousing and Pallet Racking

A warehouse fire is not as uncommon as you might think. According to the National Fire Protection Association (NFPA), an average of 1,410 warehouse fires per year were reported in the United States between 2014 and 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 can potentially cause warehouse damage, injuries, and even loss of life.

Leading Causes of Warehouse Fires

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

The Invention of Fire Sprinkler Systems

Thanks to the invention of sprinkler systems, most warehouse fires are put out safely. Sprinklers have become one of the most effective ways to reduce the potential for damage and loss of life in a warehouse fire. Luckily, the NFPA provides codes and standards used in over 50 countries, including the USA and Canada, to help facilitate the proper use of sprinklers. When considering fire safety, it’s essential to consider how your racking configuration can also impact the design and implementation of a sprinkler system.

How Do Fire Sprinklers Work?

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

Using Warehouse Storage Commodity Classification in Sprinkler System Design

The first step in determining your warehouse's sprinkler design is to identify the commodity classification of the items being stored. Commodities can be classified between Class I-IV, or Plastics A, B, or C. Plastics have a separate classification due to the high temperatures and speeds at which they burn. Classifying a commodity incorrectly is a costly mistake that can result in an ineffective sprinkler system, which cannot effectively control a fire.

The following questions are an essential 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)?
  
  

In-Rack Fire Sprinkler System Design Requirements and Limitations

Several factors must be considered when integrating a sprinkler system into your racking. The most common sprinkler systems in a warehouse are ceiling and in-rack sprinklers. In some cases, only ceiling sprinklers may be sufficient due to their larger orifice, which releases much larger water droplets that penetrate the fire more deeply than traditional sprinklers. However, ceiling sprinklers must be combined with in-rack sprinklers if the flue space requirements are not met.

Figure 3. In-rack fire sprinkler system

Figure 4. Ceiling fire sprinkler system

Warehouse Fire Sprinkler Design for Flue Space

The NFPA defines flue space as the clear vertical floor-to-ceiling openings within rack storage areas. Flue spaces are vital in fire protection since they allow heat to ventilate upward and activate a ceiling sprinkler system much more quickly, allowing water to penetrate throughout the racking system. Not having sufficient flue space can increase the chances of your fire growing horizontally, placing your racking system as a whole and everything stored 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.

Figure 5. Flue space

Depending on your specific Authority Having Jurisdiction (AHJ), you must 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 about recommended clearances in warehouses.

When Are In-Rack Sprinklers Required?

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

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

If your warehouse has undergone changes that affect these factors, the effectiveness of the fire protection system may be compromised. The building owner is responsible for identifying where these changes have occurred and informing a fire safety professional so that the fire protection system can be re-evaluated.

Considerations and Requirements For In-Rack Fire Sprinklers

Sprinkler design requirements are based on a robust set of fire test data that has established the standard for positioning in-rack sprinklers. Here are a couple of tips to position them properly:

• Ensure that the in-rack sprinkler and piping are arranged to protect from mechanical damage caused by a potential forklift accident. While ensuring that the sprinklers are protected, it is still vital that the sprinklers are in a location where 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 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 a horizontal offset of no more than 3 inches from the transverse flue space.

Seismic Considerations for In-Rack Fire Sprinkler Systems

If located in a seismic region, ensure 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, it is essential to follow proper seismic design guidance using the most recent edition of NFPA 13.

Seismic Clearances for Fire Sprinklers

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

• If the pipe diameter is between 1 and 3.5 inches, then a 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 significantly enhance the safety of your building and its occupants if you adhere to the regulations and requirements applicable 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.

Help Following Rack Safety Protocols

Therefore, as a responsible business owner, you should never overlook specific safety protocols. You can start by having your racks assessed by a Damotech engineer. The engineer can identify if your rack configuration is causing any fire protection issues and provide the necessary solutions to ensure compliance with regulations and standards as required by the appropriate authority having jurisdiction. Additionally, our Damotech-engineered rack repair kits offer a seamless and cost-effective alternative to replacing damaged racks, as they eliminate the need to reposition or dismantle your in-rack sprinkler system.

Frequently Asked Questions: Fire Sprinkler Safety Requirements in Warehousing and Pallet Racking

Why are fire sprinklers critical in warehouses?

Fire sprinklers are the first line of defense against warehouse fires. According to the National Fire Protection Association (NFPA), U.S. fire departments responded to an annual average of 1,508 warehouse fires between 2018 and 2022, translating to more than four fires daily. Sprinkler systems help minimize property loss, protect inventory, and, most importantly, save lives by controlling or extinguishing fires before emergency responders arrive.

How do warehouse fire sprinklers work?

Sprinklers activate when heat from a fire causes the glycerin-filled glass bulb inside the sprinkler head to expand and shatter. This opens a valve, releasing water onto a deflector plate that distributes it over the affected area. Each sprinkler head operates independently; only those exposed to heat activate, conserving water and maximizing efficiency.

What is commodity classification, and why is it important?

Commodity classification determines how easily your stored goods burn and what type of sprinkler system is required. The NFPA defines categories from Class I-IV and Plastics (Groups A, B, and C). Misclassifying commodities can result in an inadequate sprinkler system, increasing the risk of severe property damage or loss. Continually assess material type, packaging, pallet material, and wrapping when classifying storage commodities.

What is the difference between ceiling sprinklers and in-rack sprinklers?

Ceiling sprinklers are mounted overhead and discharge water to penetrate deep into a fire. In-rack sprinklers are installed within pallet racks to control fires ceiling sprinklers may not reach, especially when flue spaces are blocked or solid shelving is used. Using both types in high-density or tall rack systems provides the best fire protection coverage.

What are flue spaces, and why are they essential for fire safety?

Flue spaces are vertical openings between and behind pallets that allow heat and smoke to rise. This helps ceiling sprinklers activate faster and distribute water evenly.

• Transverse flue space: Between pallets within the same row.
• Longitudinal flue space: Between back-to-back rack rows. NFPA and FM Global recommend maintaining about 6 inches of clear flue space for effective sprinkler performance and fire containment.

When are in-rack sprinklers required?

In-rack sprinklers are required when ceiling sprinklers alone cannot provide adequate coverage, typically when:

• Solid shelving blocks water penetration
• Flue space is insufficient
• Storage heights exceed safe sprinkler reach
• Highly combustible materials are stored

If your warehouse setup changes (e.g., new pallet types, reconfigured racking, or different products), consult a fire safety professional to reassess compliance.

What are the key design considerations for in-rack sprinkler systems?

To comply with NFPA 13 (2019):

• Position deflectors at or just below horizontal bracing
• Avoid placing heads directly behind uprights or more than 3 inches off-center from flue spaces
• Protect sprinkler heads and piping from forklift impacts while maintaining discharge effectiveness
• Ensure adequate water pressure and coverage based on commodity type and rack height

What are the seismic clearance requirements for sprinkler piping?

In seismic regions, sprinkler piping must have proper clearance to prevent damage during an earthquake:

• 2 inches for pipe diameters between 1 and 3.5 inches
• 4 inches for pipe diameters 4 inches or larger

Follow NFPA 13’s seismic design guidelines to reduce risk and extend system service life.

How often should warehouse sprinkler systems be inspected?

According to NFPA 25, warehouse sprinkler systems should be inspected annually from floor level by qualified professionals. Frequent visual checks by maintenance staff can help identify leaks, corrosion, or obstructions. Routine inspections ensure system readiness and regulatory compliance.

How does racking configuration affect sprinkler performance?

Improper racking layouts, such as blocked flue spaces, solid shelving, or uneven load spacing, can severely restrict sprinkler efficiency. Regular rack inspections can identify whether your configuration complies with NFPA 13 and local codes, helping prevent fire spread and ensuring insurance compliance.

Who is responsible for ensuring warehouse fire sprinkler compliance?

The building owner is ultimately responsible for maintaining fire protection systems and ensuring they remain effective after any operational or layout changes. This includes notifying fire safety engineers of any modifications impacting sprinkler performance or coverage.

How can Damotech help with warehouse fire protection compliance?

Damotech’s engineering team can assess your rack systems to ensure compliance with fire safety codes and flue space requirements. If damage is found, Damotech’s engineered rack repair kits allow repairs without dismantling or repositioning in-rack sprinklers, minimizing downtime and maintaining safety compliance.

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