Flue Space — Definition & Types

Flue Space — Definition & Types

Flue Space describes the engineered gaps, channels and vertical voids created within pallet racking and modular storage systems. These spaces are not incidental; they are intentional design features used to support life safety, environmental control, material handling efficiency and utility routing.

In warehouse and distribution environments the term commonly applies to the vertical openings between pallet loads, between decking and beams, or between rack uprights and wall infrastructure. Flue space functions include enabling fire sprinkler water to penetrate loads, permitting free airflow for temperature and humidity control, and providing safe pathways for electrical, data and mechanical services.

Flue space is a cross-disciplinary concept touching structural engineering, fire protection, HVAC, and warehouse operations. When designed in concert with pallet load patterns and racking components, flue space reduces product damage, improves energy efficiency, and ensures compliance with regulatory standards that address sprinkler effectiveness and smoke movement.

Primary types of flue space

• Inter-pallet vertical flues — The vertical gaps intentionally left between stacked pallets or between palletized loads and the level above. Often created by pallet overhang control, tiered stacking, or use of pallet spacers. These flues are critical for allowing sprinkler spray to reach lower levels of stored goods and for channeling heated gases during a fire.

• Rack-bay vertical channels — Continuous vertical openings that run the height of a rack bay, formed by the alignment of pallet loads or by using open-frame uprights and selective beam spacing. Rack-bay flues are commonly preferred in high-bay warehouses to maintain sprinkler coverage and HVAC distribution.

• Beam-to-beam flues — Narrow vertical gaps engineered between beam levels by using stepped beams or partial decking. These are useful in selective racking where full-pallet fire compartmentalization is impractical.

• Perforated decking and mesh-supported flues — Use of wire mesh decking or perforated panels creates micro-flue spaces that permit water and air to pass while providing load support. This approach balances product containment with sprinkler access.

• Service and cable flues — Dedicated channels integrated into rack infrastructure for routing power, data, sensors and pneumatic tubing. These flues are often hidden within column cavities or along uprights to protect services from mechanical damage while maintaining accessibility.

• Seismic/expansion flues — Gaps introduced to accommodate building movement, thermal expansion, or seismic displacement. While primarily structural, these flues can also intersect with fire and airflow considerations and must be coordinated with other systems.

Functional roles and examples

In fire protection, authorities such as the National Fire Protection Association (NFPA) rely on adequate flue space to ensure sprinkler water distribution. For example, high-piled storage of boxed goods often requires specific vertical flue dimensions and alignment so that water can penetrate the commodity and control fire growth. In temperature-sensitive operations, such as cold storage, flue spaces are designed to maintain consistent airflow from evaporators and avoid cold pockets that cause product quality issues.

From an infrastructure perspective, flue space intersects with rack components: selecting open-back uprights, using stepped beams that leave a channel, or specifying mesh decking creates or preserves flues. An electronics distribution center may integrate narrow service flues adjacent to uprights to carry Ethernet cabling and environmental sensors, while an e-commerce fulfillment center may use broad inter-pallet flues to improve warehouse ventilation and reduce HVAC load.

Design considerations

• Regulatory compliance — Confirm local and national fire and building codes, and consult NFPA standards where applicable. Specific commodities may be classified as high-challenge and require additional flue spacing or alternative suppression designs.

• Commodity characteristics — Pallet footprint, packaging permeability, combustibility and pallet configuration all influence required flue dimensions to achieve sprinkler effectiveness.

• Rack geometry and components — Beam spacing, deck type, upright profiles and accessory use (such as pallet stops or row spacers) will determine achievable flue patterns.

• Operational workflows — Picking methods, forklift pathways and pallet turnover affect whether continuous flue spaces are feasible without impeding throughput.

• Integration with utilities — Plan flues to accommodate power, lighting and sensor paths without compromising structural integrity or fire safety.

Practical examples

• A cold-chain warehouse used stepped beams to create continuous flue channels, enabling even cold-air distribution and reducing product spoilage by stabilizing temperature gradients across rack heights.

• An apparel distribution center specified perforated decking to provide both load support and micro-flue passages that allowed sprinklers to reach deeper within packed cartons, helping the facility meet stringent fire code requirements.

Conclusion

Flue space in advanced infrastructure and rack components is a purposeful design element with multiple safety and operational benefits. Properly specified flues improve sprinkler penetration, airflow management, utility routing and seismic performance. Effective implementation requires coordination between facility design, fire protection engineers, racking suppliers and operations managers to balance safety, cost and productivity.