Rack Storage In-Rack Sprinkler Design: NFPA 13 High Fire Load Solution

Modern distribution centers store products 12-15 meters high. Water from ceiling sprinklers meets densely smoked cartons before reaching the rack fire. That is why high-bay warehouses require in-rack sprinklers. NFPA 13 Section 17 defines detailed design requirements for various rack types and storage classes. An engineer's overview of in-rack design below.

Why In-Rack Is Required

• High rack: fire spreads within rack before reaching ceiling sprinklers
• Flue space (vertical air gap in rack): acts like a chimney, pushing fire up
• Ceiling sprinkler: water can't penetrate deep into rack — fire continues inside
• In-rack: delivers water directly to the fire source

Commodity Class

NFPA 13 classifies stored goods by combustibility:

• Class I: Metal/glass products on metal shelves (low combustibility)
• Class II: Wood pallet or cardboard carton
• Class III: Cartoned product in plastic wrap
• Class IV: Class I-III or Group A plastic ≤25% by volume
• Group A Plastic: High combustibility — ABS, polyethylene, polystyrene
• Group B/C Plastic: Moderate/low combustibility

Rack Types

• Single row rack: One row, accessible from both sides
• Double row rack: Two rows sharing same uprights
• Multiple row rack: 3+ rows back to back
• Solid-shelf rack: Impermeable shelf; in-rack mandatory, ceiling alone insufficient

In-Rack Sprinkler Levels

NFPA 13 tables specify how many in-rack levels are required per rack height and commodity class:

• Class I, 6m rack → ceiling sprinkler only sufficient
• Class IV, 9m rack → in-rack level 1 (at 3m or 3.6m height)
• Group A plastic, 12m rack → in-rack every 3m (multi-tier)
• Solid shelf: in-rack at every level

ESFR vs In-Rack

ESFR (Early Suppression Fast Response) penetrates rack depth with high flow. An alternative to in-rack:

• ESFR pro: Ceiling only, no in-rack piping, no forklift damage to pipes
• ESFR con: Doesn't work at low ceiling height (<9m); hat/carton obstruction risk
• In-rack pro: Works at any rack height, suits low ceilings
• In-rack con: Complex piping, hard to maintain, forklift pipe damage

Solution: Most modern DCs use ESFR ceiling + in-rack combination or ESFR only (high-bay warehouse).

Turkey Logistics Warehouses

New 3PL warehouses in organized industrial zones are quickly adopting ESFR + in-rack combos. Older warehouses typically have ceiling sprinklers only — no in-rack. When a Group A plastic fire starts, the ceiling system is insufficient.

Common Mistakes

1. Commodity class understated: Group A plastic logged as Class III.
2. Rack raised, system not updated: Went from 6m to 9m; in-rack tier required.
3. Flue space blocked: Rack gaps filled; fire geometry changed.
4. Forklift pipe damage: Crushed in-rack pipe, no water in fire.

Conclusion

In-rack sprinklers are an indispensable complement to ceiling systems in high-bay warehouses. With correct NFPA 13 table application, Class IV and Group A plastic fires can be controlled. Any design without a correct commodity class definition is incomplete.

In-rack design in SprinkCalc

Commodity class selection, rack height and tier calculation, ESFR comparison analysis.

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