Flue Space Specifications

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

There are two types of rack flue spaces:

  1. Longitudinal – the spaces between two rows of racks
  2. Transverse – the spaces between pallets or rows of storage in the direction of loading

Historically, most pallet rack systems have been designed with even spacing between loads and upright frames (see Figure 2).

However, the National Fire Protection Association (NFPA) requires that pallet rack flue space remain clear at all times so that in case of a fire, they can successfully vent upward rather than out, allowing sprinkler systems to activate faster.

According to the NFPA, there must be a six-inch horizontal flue space between loads in a rack structure (see Figure 3).

Unless in-rack sprinklers are installed below each storage level, flue spaces are necessary when implementing storage racks to allow heat from a fire to vent vertically rather than outward.

By doing so, this also ensures that ceiling level sprinklers will operate as quickly as possible to slow down the horizontal fire spread within the racks.

Flue spaces are also important in allowing sprinkler water to reach the base of the fire down through the racks.

Without adequate water reaching the burning materials on the lower levels, the harder it will be to control the fire  (see Figure 4).

Poor rack design and overly deep pallet loads can play a major role in flue space obstruction.

A well-designed racking system that is compliant with city codes and NFPA regulations will reduce the potential for significant property damage and prevent business interruptions caused by inadequate flue spaces.