A flue space divider is a physical stop that holds the vertical gap in a pallet rack open, so a pallet can't be pushed into the space your sprinkler system needs.
That's the whole idea. Everything else is about which one to use where, and there are two different products doing two different jobs, which is where most of the confusion lives.
Why a Physical Stop, and Not a Rule
Flue space is easy to specify and hard to keep. It closes through ordinary work: a driver seats a pallet a few inches deeper than the last one, the next load goes in against it, and the gap's gone. From the aisle nothing looks wrong, because the faces still line up. Nobody made a decision and nobody knows.
Which is why the control has to be physical. A written procedure depends on every driver judging depth correctly on every put-away through a peak season. A stop bolted to the rack doesn't depend on anything. It also gives the driver something useful: a positive stop to seat against instead of a guess.
The secondary benefit is the one operations people care about more. The same stop that protects the flue prevents pallet push-through, where a load gets driven out the back of a bay into the row behind or off the rack entirely. That's a product-damage and falling-object problem long before it's ever a fire-code problem.
Flue Guard vs Flue Keeper
Both hold flue space. They hold different flue spaces, and that's the distinction worth getting right:
| Flue Keeper | Flue Guard | |
|---|---|---|
| Holds | Transverse flue, at the rack upright | Longitudinal flue, back-to-back between rows |
| Geometry | ~3 in. each side of the post, the nominal 6 in. total | Holds the back-to-back gap in a double-row rack |
| Also does | Pallet safety stop at any elevation | Back stop against pallet push-through |
| Reach for it when | You need the flue held at the columns | You're stopping loads pushing into the row behind |
If you're only going to do one, the answer depends on your racks rather than on preference. And if your storage is over 25 feet, you probably need both. The flue products range covers each, and transverse flue space and fire sprinklers explains why the transverse gap is the one that exists in every configuration.
What the Code Actually Asks For
Worth knowing before you buy, because the requirement is narrower than most people assume and it splits at 25 feet of storage height.
Up to and including 25 ft
- Nominal 6-inch transverse flue spaces between loads and at rack uprights, in single-row, double-row and multiple-row racks alike.
- No longitudinal flue required in double-row and multiple-row racks without solid shelves. The open rack already passes water. This surprises people, and it means the back-to-back gap isn't always the thing you need to solve.
Over 25 ft
- Nominal 6-inch transverse flue spaces, as above.
- Nominal 6-inch longitudinal flue spaces in double-row racks.
NFPA 13 says nominal deliberately, and permits random variation in flue width and vertical alignment, because in-rack sprinkler piping and rack members intrude by design. Solid or slatted shelving changes the analysis, as do commodity class and sprinkler type. Screen your arrangement with the flue space calculator, and see pallet rack spacing requirements for the rest of the clearances.
Your AHJ is the authority here and states amend the model codes. Confirm before you design to any of it.
The Storage You Think You're Gaining
The argument against flue dividers is always the same: that gap is sellable cube, and a stop makes giving it up permanent.
It's worth being honest that the trade is real. You are giving up depth. What you get back isn't only code compliance:
- Loads stop where they're supposed to, so retrieval is predictable and the rear of the bay isn't a mystery.
- Nothing exits the back of a rack, which becomes a containment problem the moment it happens near an aisle or a walkway.
- Bays load consistently, because every position has the same usable depth instead of whatever the last driver left.
The cube you gain by closing a flue is cube you can't legally use once an inspector sees it. It's also the same cube that stops your sprinklers working in the fire that justifies the whole system.
Not sure which of the two your racks actually need? Tell us your rack type, storage height and whether you've got solid shelving, and we'll work it out with you. Get in touch.