As industries expand and facilities evolve to meet growing logistical demands, high-piled combustible storage (HPS) has become increasingly common across various occupancy types—ranging from traditional warehouses and fulfillment centers to manufacturing, big-box retail, and shipping hubs. Despite its widespread use, high-piled storage remains one of the most commonly misunderstood and improperly managed fire protection hazards, often due to overlooked code requirements, misclassified commodities, or incomplete plan submittals.

As a fire protection professional with over 18 years of experience in design, consulting, and enforcement, I have seen first-hand how noncompliance—intentional or otherwise—can lead to serious delays, rework costs, and safety risks. This article aims to shed light on key HPS requirements, commonly missed items, and actionable strategies to improve compliance, protect lives, and support first responders.

Understanding High-Piled Combustible Storage

The definition of high-piled combustible storage may seem straightforward, but it carries nuanced implications across the International Fire Code (IFC) and NFPA 13—and missing those distinctions can lead to incorrect assumptions during design, construction, or enforcement.

In IFC (2024 Edition) Section 202, High-Piled Storage is defined as “Storage of combustible materials in closely packed piles or combustible materials on pallets, in racks or on shelves where the top of storage is greater than 12 feet in height. For high-hazard commodities such as Group A plastics, rubber tires, idle pallets, and flammable liquids, the threshold is reduced to 6 feet when required by the fire code official.”

In short:

• 12 feet is the general threshold for HPS (most common commodities).
• 6 feet applies to certain high-hazard commodities—subject to the fire code official’s discretion (i.e., plastics, flammable liquids, rubber tires, etc.).

NFPA 13 (2022 Edition) further classifies (for sprinkler design purposes only, not for a classification of storage arrangement):

• High-piled storage: Class I–IV commodities above 12 ft, or Group A plastics above 5 ft.
• Low-piled storage: Below those same height thresholds.

Important note:

These definitions affect both operational permits and sprinkler design criteria, and inconsistencies in application are common causes of approval delays. Also, HPS areas that are <500 sq ft typically do not require an HPS permit. Always check with the local Authority Having Jurisdiction (AHJ) for local specifics and requirements.

Why High-Piles Storage Planning Matters

High-piled storage environments introduce a significantly greater fire load and hazard complexity than low-level storage. Fires in HPS areas tend to spread rapidly, often vertically and across multiple tiers, while impeding sprinkler performance and fire department operations.

Two major objectives drive HPS regulation:

Life Safety: Ensuring occupants can evacuate quickly and safely.

Firefighter Preparedness: Providing responders with clear knowledge of what is stored, how it is stored, and what protective systems are in place.

Without clear documentation and preplanning, firefighting operations can become exponentially more dangerous and ineffective.

Permits: The Most Common Compliance Gap

Permits for HPS fall under two main categories:

 Operational Permits: Required when over 500 square feet of HPS is in use (including aisles). This is only required after the building has been erected and the facility is looking to start stocking. This is typically submitted after the building is done and is a deferred submittal from the building package.

Construction Permits: Required when a facility is being built or modified to include over 500 square feet of HPS and is required to be submitted at time of construction (whether deferred or as part of the building package).

Due diligence performed at the onset of the project will help determine when and how the HPS package is to be submitted.

These requirements are detailed in IFC 105.5.24 and 105.6.14, and yet many businesses continue to overlook them. Incomplete or inaccurate permit applications are the most common cause of project delays.

Items Commonly Missed in HPS Permit Submittals:

Floor plan showing HPS locations, dimensions, and access doors

Storage height and clearance to sprinkler deflectors

Commodity classification and separation of different types of commodities (as needed)

Aisle width measurements and flue space configuration

Sprinkler system design info (e.g., in-rack vs. ceiling)

Fire department access features, hydrants, and FDCs

 NFPA 704 signage for hazardous materials

 Fire alarm and smoke/heat venting details (fusible link temperature ratings, etc.)

Evacuation plans for applicable occupancies

Racking details (to include plan and elevation views, number of tiers, means of protecting flue spaces, any racking calculations to include structural and seismic)

Permit reviewers are increasingly requiring these documents upfront, and AHJ

Storage Types and Flue Space Maintenance

How you store materials directly affects fire behavior and code requirements. NFPA 13 and IFC Section 3208.3 outline acceptable storage arrangements and their spacing needs:

Common Storage Types:

Palletized: Stored on pallets with voids between stacks.

Solid-piled: No pallets or voids; stacks directly on each other.

Rack Storage: Requires careful flue space management.

Shelf Storage: 30 in. max depth with vertical spacing.

Back-to-Back Shelf: Requires solid barriers and separation.

Bin Box Storage: Self-contained storage units with minimal voids.

Flue Spaces:

• Longitudinal: Front-to-back through racks (parallel to the loading aisle)
• Transverse: Side-to-side between racks (perpendicular to the loading aisles)

Flue spaces work by serving two purposes: heat from the fire rising up to the sprinklers, to allow for detection and reaction, and to let water from above fall to the where it is needed. Both types are critical for sprinkler discharge to reach the seat of the fire. If improperly maintained (blocked or oversized), sprinkler effectiveness is greatly reduced. Code allows a maximum 24-inch flue space; anything more is considered an aisle (for fire protection purposes) and may require added protection.

Commodity Classification Pitfalls

Commodity misclassification can render a sprinkler design invalid, particularly when packaging materials or pallet types are not fully considered.

Examples:

• Plastic pallets (unreinforced): Increase classification by one level.
• Plastic pallets (reinforced): Increase by two levels (to a maximum classification of Group A Plastics).
• Mixed commodities or excessive Group A plastics may require design adjustments.

Accurate classification ensures the correct sprinkler design density and storage limitations. IFC Table 3206.2 and NFPA 13, Chapter 5 serve as your guides here.

Smoke and Heat Venting Requirements

Smoke and heat vents (SHV) are often overlooked in both design and maintenance. These are required to provide a safe means of venting smoke and heated gasses from the fire. According to IFC Chapter 910 and Section 3206.8, buildings using high-piled storage must include:

• Mechanical exhaust systems or gravity vents
• Fusible links rated at 360°F when in sprinklered buildings
• Annual inspection and five-year function testing (for mechanical systems)

Many jurisdictions now require documentation of SHV inspections to be stored onsite in a consolidated report. Failure to maintain these vents can reduce or nullify their effectiveness during a fire event.

Housekeeping and Ongoing Compliance

High-piled storage is not “set it and forget it.” IFC 3205 mandates that the storage layout be:

• Verified annually
• Any changes approved prior to the onset of “work”.

Common violations include:

• Storing above designated height lines
• Blocking flue spaces or egress paths
• Stacking idle pallets too high
• Inadequate signage or fire extinguisher placements
• Missing or inaccurate zone maps

Each of these can lead to a failed HPS inspection during either the final, or annual HPS inspection with the local AHJ.

Final Walk-Through: Are You Ready?

When it’s time for the final inspection with your Authority Having Jurisdiction (AHJ), a failed walkthrough can delay occupancy or even result in temporary shutdowns.

Final Checklist:

• Posted hard copies of approved HPS drawings
• Marked maximum storage heights
• Visible exit signage and clear egress
• Correct fire extinguisher locations
• Access maintained to FDCs and fire lanes
• Inspection/test records for sprinklers, alarms, and SHVs
• Commodity and aisle compliance verified

Even seemingly minor issues—like an unmarked flue space or missing fire alarm labels—can become major project setbacks by “failing” the final HPS inspection or increase the risk of danger related to a fire event by increasing risk to life and property.

Conclusion: Staying Ahead of the Curve

As HPS regulations evolve and enforcement becomes more rigorous, the industry must respond with proactive planning, accurate classification, and diligent documentation. Whether you’re designing a new storage facility or operating an existing one, compliance is not a one-time task; it’s an ongoing responsibility. Any HPS requirements in the jurisdiction in which you are planning, a conversation at the start of the HPS analysis is extremely beneficial to avoid these pitfalls and mistakes.

Fire protection professionals, facility managers, and design teams must work in unison to ensure not only regulatory compliance but also life safety and operational continuity.

If you are unsure whether your facility meets HPS requirements, consider a third-party review or consult your local fire authority. Catching and correcting these issues early can save time, money, and potentially lives.