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The Importance of Pallet Rack Row Flue Space – and Ways to Maintain it

Flue spaces are clear vertical lines of sight from the floor up to the ceiling within rack storage areas

Rack Inquiry

Pallet rack fire and flue space illustration

The National Fire Protection Association (NFPA) has long required that pallet rack flue space should remain clear at all times so that any fires can successfully vent up rather than out, allowing sprinkler systems to activate faster. This vertical rise also helps slow fire spreading horizontally through a rack system. Flue space compliance is increasingly important to insurers and operators of warehouses and other industrial facilities. What can you do to help reduce issues with flue space obstruction?

There are two types of pallet rack flue space:

  1. Longitudinal: these are the spaces between rack rows set perpendicular to the direction of loading. They’re simply the space between two rows of racks.
  2. Transverse: these flues are the spaces between pallets, and between pallets and uprights, facing the storage aisle.

Poor rack design and overly deep pallet loads

Be certain your pallets and loads are the right size for the depth of your rack.

Well-designed storage systems allow the pallet to hang over the back beam in a double row, and maintain adequate longitudinal flue space between rows. While the required longitudinal space may depend on local fire regulations and overall height and relate to the rack’s transverse flue space, the most common space is 6″ between loads, which means that the space between rack uprights has to be greater than that.

Row spacers are frequently installed to produce precise longitudinal flue space. To be effective, that space must have been correctly designed and the pallets within restrained so that they do not block a clear line, top-to-bottom longitudinal flue. Pallet push-through can result in blocked longitudinal flue space, even if the rows are adequately spaced.

One mistake that is commonly made is to use a solid rack decking, which will encourage horizontal flame spread and will not allow sprinkler systems to adequately function.

How do you combat that?

rack flue space

Loading and forklift driver errors

One of the most common ways that longitudinal flue space gets choked is pallet push-through. This is a problem that isn’t difficult to solve, assuming that your pallet loads are not too deep for your rack system.

  • Some warehouses opt for an extra beam installed at the back of each bay for a more rigid solution. One issue with this is that it rigidly limits the size of pallets to very little overhang. It’s an easy way to go about it, but it is a very limiting method.
  • One of the easiest solutions is to install inexpensive rack straps that attach to the back of each rack bay. These straps have give to them, which helps the driver understand that he has pushed the pallet back far enough without damaging the rack.
  • Rack safety nets can also restrain loads away from the longitudinal flue when installed on the back of rack rows. These cover the entire bay, and are more frequently used to stop product falls on the outer aisles.
  • Also, there are bolt-on brackets that attach to step beams to limit the movement of a pallet into flue space.

Keep in mind that the more flexible options are likely more preferable from a rack safety standpoint. Both nets and straps give as a forklift pushes a pallet too hard into them, which takes pressure off the rack. They may even fail, but that is preferable to warping or damaging a rack’s steel components.

More information on rack flue space

Pallet Rack Pages

Scott Stone is Cisco-Eagle's Vice President of Marketing with more than thirty years of experience in material handling, warehousing and industrial operations. His work is published in multiple industry journals an websites on a variety of warehousing topics. He writes about automation, warehousing, safety, manufacturing and other areas of concern for industrial operations and those who operate them.

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