The purpose of pallet rack flue spaces is to reduce fire damage: flue spaces help flames to vent up rather an out, creating a vertical rise that helps slow down the horizontal spread, allowing ceiling sprinklers (as well as any in-rack sprinklers) to activate faster. Flue spaces also allow water from the sprinklers to reach the warehouse racking and burning materials without obstructions.

Types of Flue Spaces

Flue spaces are clear lines of sight from the floor up to the ceiling within rack storage areas. There are two types of flue spaces: transverse flues and longitudinal flues. Transverse flue spaces are the spaces on either side of a pallet. Longitudinal flue spaces are the spaces between back to back rows.

Flue Space Requirements

Pallet rack flue spaces are required by the National Fire Protection Association (NFPA), but the requisite minimum flue space can vary by a location ‘s code requirements. Different municipalities may have different requirements for flue spaces, but in general, unless in-rack sprinklers are provided at every storage tier, NFPA standards require transverse flue spaces in all storage rack regardless of building and storage height. Transverse flues should be set to a minimum of 3 inches, with 6 inches being preferable. Six inches may be required for deeper or taller rack, or if no longitudinal flue spaces are used.
Longitudinal flue spaces, on the other hand, are optional for double-row and multi-row rack storage without solid shelves, up to 25 feet tall. Longitudinal flues should be set to a minimum of 6 unobstructed inches. If the space between two rack structures is more than 24 inches, the space should be treated as an aisle for in-rack sprinkler design and installation purposes.
NFPA standards permit random variations in the width of the flue spaces or in their vertical alignment for both traverse and longitudinal flue spaces.

Maintaining Flue Spaces

In a standard pallet rack configuration there is normally pallet overhang front and back, and this must be calculated into into the longitudinal flue space. Typical pallet overhang is 3 inches, making your actual required flue space from back to back 12 inches. Row spacers are often installed to produce more precise longitudinal flue spaces.
But even with row spacers, longitudinal flues can be hard to maintain due to pallet “push-through which is created when a forklift pushes a pallet too far back upon loading, causing the flue width to be lessened. There are ways to prevent push-through, such as installing pallet stop beams, pallet stops, or wire rack guards.
Changing the size of pallets or the way product is stacked in your pallet rack can also affect both longitudinal and transverse flue spaces, thus reducing the sprinkler system ‘s ability to perform effectively in the event of fire. Always be aware of your flue spaces when making such changes.
Next Level has everything you need for maintaining a safe warehouse, including row spacers, stop beams, pallet stops, and wire rack guards to ensure your flue spaces maintain the correct widths. For more information about pallet rack accessories, contact us here or call 800-230-8846 now to speak to a Next Level warehousing expert.
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