Pallet fire safety: idle pallet storage, NFPA 13, fire codes and UL 2335
Stacks of idle pallets burn fast and hot, so NFPA 13 and fire codes treat them as a special hazard. Store them outdoors or in a detached building where possible; indoors they need specific sprinkler protection. Unlisted plastic pallets count as a higher hazard than wood. Confirm with your AHJ.
Pallet storage is one of the fire hazards fire marshals and insurers look at first in a warehouse, a manufacturing plant or a pallet yard. This guide explains why, how the main codes approach it, and what a pallet buyer or warehouse manager should ask. It is a plain-language overview, not code advice: requirements depend on the code editions your jurisdiction has adopted and on your building.
Always confirm idle pallet storage arrangements with your authority having jurisdiction (AHJ), your property insurer and a qualified fire protection engineer. The details below are general and edition-dependent.
Why are idle pallets a fire hazard?
An idle pallet is an empty pallet waiting to be used, repaired or collected. A stack of idle pallets has:
- A lot of fuel. A 48 × 40 in (1219 × 1016 mm) wood pallet weighs roughly 30–70 lb (14–32 kg). A stack of 20 holds 600–1,400 lb (270–640 kg) of wood.
- A large surface area. Thin deckboards and open gaps expose more wood to the flame than solid lumber.
- Built-in airflow. Openings between deckboards and stringers act like flues.
- Shielded interiors. Sprinkler water falls on the top deck while the fire burns inside the stack.
The result is fast fire spread and a high heat release rate, which is why fire test programs treat idle pallets as a demanding commodity. Plastic pallets add higher heat of combustion and melting, burning plastic.
How NFPA 13 treats idle pallets
NFPA 13 is the US standard for sprinkler system design. It addresses idle pallet storage separately from stored goods. In broad terms, current editions:
- Prefer that idle pallets be stored outdoors or in a detached structure.
- When idle pallets are stored indoors, require sprinkler protection designed specifically for idle pallet storage, with design criteria that depend on pallet material (wood or plastic), stack height, ceiling height and sprinkler type.
- Treat unlisted plastic pallets as a higher hazard than wood. Plastic pallets that are listed as equivalent to wood (see UL 2335 and FM 4996 below) can be protected like wood pallets.
- Generally do not allow idle pallets to be stored in racks unless the protection design specifically addresses it.
- Address loaded plastic pallets too: unless listed, plastic pallets under stored goods can raise the commodity classification by one or two classes, which increases the sprinkler density needed.
Specific stack heights, clearances and design densities are set in NFPA 13's tables and vary by edition. Your fire protection engineer applies them to your building.
How fire codes treat pallet storage
The International Fire Code (IFC), adopted in most US states with local amendments, has provisions for pallet storage in two places:
- Indoor storage is handled through high-piled combustible storage rules and by reference to NFPA 13. Plastic pallets can trigger high-piled storage requirements at lower heights than other commodities, reported at 6 ft (1.8 m) in some adopted codes.
- Outdoor pallet storage provisions, added in recent editions, cover pallet yards at manufacturing and recycling sites and outdoor storage at other facilities. They include site plans, fire prevention and security plans, pile size and height limits, and separation distances from buildings, lot lines and other piles, with separate tables for wood and plastic pallets.
Some jurisdictions use the NFPA 1 Fire Code instead of the IFC. Both lead back to NFPA 13 for sprinkler design.
UL 2335 and FM 4996: listed plastic pallets
Two test programs let a plastic pallet be treated as equivalent to wood for sprinkler design:
| Program | Owner | What it shows |
|---|---|---|
| UL 2335, Fire Tests of Storage Pallets | UL Standards & Engagement | Idle-pallet and commodity burn tests showing the pallet performs no worse than wood under the tested protection |
| FM 4996 (Approval Class 4996) | FM Approvals | Idle plastic pallet fire test showing equivalence to wood pallets |
Fire code text derived from the IFC states that plastic pallets listed to UL 2335 or FM 4996 are treated as wood pallets for determining required sprinkler protection. Pooled iGPS plastic pallets, for example, are marketed as UL 2335-listed.
If you buy plastic pallets for indoor storage in any quantity, ask for the listing and keep the certificate on file. "Fire-retardant resin" on its own is not a listing. See the plastic pallet buying guide.
Practical idle pallet storage rules
These are widely used good practices from insurers and fire safety guidance. They do not replace the code requirements that apply to your site.
| Practice | Why |
|---|---|
| Store idle pallets outdoors, away from buildings, where possible | Removes the largest fuel load from the building |
| Keep indoor idle pallet stacks low and flat, on the floor | Lower stacks are easier for sprinklers to control |
| Keep clear of sprinklers | Maintain the clearance below sprinkler deflectors your design requires |
| Do not store idle pallets in racks unless designed for it | Racks create flue spaces and shield the fire |
| Separate stacks and keep aisles | Limits spread between piles |
| Do not stack pallets against exterior walls, doors or under canopies | A yard fire can enter the building |
| Keep the idle pallet count down | Return, recycle or sell surplus pallets; see pallet recycling and sell used pallets |
| Segregate plastic and wood pallets | They may need different protection |
| Control ignition sources | No smoking, hot work permits, keep battery chargers and heaters away |
| Keep the yard clean | Remove broken pallets, sawdust and debris |
Pallet yards at pallet companies
Pallet manufacturers and recyclers keep large quantities of idle pallets outdoors, which is why outdoor pallet storage provisions exist. If you buy from or sell to such a yard, a well-run site will have organized piles, clear fire lanes and space between piles and buildings.
Wood vs plastic vs other materials
| Material | Fire behavior in storage | Code treatment (typical) |
|---|---|---|
| Wood | Burns fast as idle stacks | Baseline for idle pallet protection |
| Plastic, unlisted | Higher heat release; melts and pools | Treated as a higher hazard; raises commodity class |
| Plastic, UL 2335 or FM 4996 listed | Tested as no worse than wood | Treated as wood in many adopted codes |
| Metal | Does not burn | Low fuel contribution |
| Paper / corrugated | Burns readily | Cellulosic; check with your engineer |
Switching from wood to unlisted plastic pallets can make an existing sprinkler system inadequate. Involve your fire protection engineer before you change pallet material.
Fire-retardant wood pallets?
Fire-retardant treatment of wood pallets is rarely specified. Storage fire safety is usually handled through sprinkler design and storage arrangement rather than treated pallets. If an engineer asks for treated pallets, specify the treatment and test standard explicitly.
What to ask before buying pallets for a sprinklered warehouse
- What pallet material and listing does our sprinkler design assume?
- How many idle pallets can we store indoors, where, and how high?
- If we switch to plastic, are the pallets listed to UL 2335 or FM 4996?
- Does our insurer have its own requirements?
- Are our outdoor pallet piles far enough from the building and lot lines under the adopted fire code?
Specifying it for a quote
On a pallet RFQ, include:
- Material (wood, plastic, metal)
- For plastic: required fire listing (UL 2335, FM 4996 or either), with certificate
- Quantity to be stored idle on site, if you want the supplier to plan deliveries to limit on-site stock
- Take-back or recycling service for surplus and broken pallets
For how different materials compare in other respects, see plastic vs wood pallets.
Frequently asked questions
Why are idle pallets such a fire hazard?
An empty pallet stack is mostly air and thin wood or plastic with a large exposed surface, much like a stack of kindling. Fire spreads through it quickly and releases heat fast, and sprinkler water has trouble reaching into the stack.
Can I store empty pallets in my pallet racks?
NFPA 13 generally does not permit idle pallet storage in racks unless the sprinkler design specifically covers it. Check with your fire protection engineer before racking empty pallets.
Are plastic pallets more of a fire risk than wood?
Unlisted plastic pallets are treated as a higher hazard than wood in NFPA 13 and fire codes, raising the commodity class and sprinkler demand. Plastic pallets listed to UL 2335 or FM 4996 can be treated as equivalent to wood under many adopted codes.
Who decides what my building needs?
The authority having jurisdiction (AHJ), usually the local fire marshal or building official, together with your insurer and a fire protection engineer, based on the codes your jurisdiction has adopted.
Sources and references
- NFPA 13, Standard for the Installation of Sprinkler Systems (National Fire Protection Association)
- International Fire Code, outdoor pallet storage provisions (International Code Council)
- UL 2335, Fire Tests of Storage Pallets (UL Standards & Engagement)
- FM Approvals Class 4996, Classification of Idle Plastic Pallets as Equivalent to Wood Pallets (FM Approvals)
Related
- StandardsUL 2335: fire tests of storage palletsUL 2335, Fire Tests of Storage Pallets, tests how pallets contribute to fire in idle, palletized and rack storage protected by NFPA 13 sprinklers. Plastic pallets listed to UL 2335 or FM 4996 are treated like wood when sizing sprinklers; unlisted plastic raises the commodity class.
- GlossaryUL 2335UL 2335 is the UL standard for fire tests of storage pallets. Plastic pallets listed to UL 2335, or approved to FM 4996, can be treated as equivalent to wood pallets when fire codes set sprinkler protection, while unlisted plastic pallets can raise the required protection.
- TypesPlastic pallets: types, materials, load ratings and how to buy themA plastic pallet is a molded or fabricated pallet made from HDPE or polypropylene. Types range from light nestable pallets (about 14–30 lb) to reinforced rackable pallets (about 35–70 lb). They are washable, ISPM 15 exempt and long-lived, cost several times more than wood, and carry three separate load ratings.
- GuidesPlastic pallet buying guide: styles, resins, ratings and costChoose a plastic pallet by how it is handled and stored: nestable for cheap one-way use, stackable for floor stacking, rackable for open-beam racking. Compare static, dynamic and racking ratings only when the test standard and support match. New US prices run about $40–200 (2026 estimates).
- ComparisonsPlastic vs wood pallets: cost, strength and when to use eachChoose wood when you need the lowest price, a custom size, easy repair or one-way shipping. Choose plastic when pallets run in a closed loop for many trips, when hygiene and washability matter, when you need consistent dimensions for automation, or to avoid ISPM 15 treatment on exports.
- GlossaryWhat is pallet racking?Pallet racking is a steel storage structure of upright frames and horizontal beams that holds loaded pallets in levels above the floor. The pallet usually spans the gap between two beams, so its racking load rating, not its floor rating, governs.
- GlossaryBlock stackingBlock stacking is storing unit loads directly on top of one another on the warehouse floor, in rows and columns, with no racking. The bottom pallet and the packaging carry the whole stack, so static load and box compression strength limit the height.
- GuidesPallet recycling: how used pallets are repaired, rebuilt and groundUsed wood pallets are widely recycled in the US. Recyclers collect them, sort by size and grade, repair the good ones for resale, dismantle damaged ones for parts to build remanufactured pallets, and grind the rest into mulch, animal bedding or biomass fuel. Businesses usually get free pickup or payment for full loads.
More in Compliance and safety
- GuidesHeat-treated pallets (HT): what they are, when you need them, and costA heat-treated (HT) pallet's wood core was held at 56 °C (133 °F) for 30 minutes under ISPM 15, then stamped with the IPPC mark and HT. Most countries require it on wood pallets crossing their border. It adds roughly $1–3 per pallet (2026 US estimate) and kills pests; it does not dry the wood.
- GuidesPallet stamps and markings: HT, MB, DB, KD and what they meanMost wood pallet stamps are the ISPM 15 mark: IPPC wheat symbol, country code, facility number and treatment code. HT means heat-treated, DH dielectric heating, MB methyl bromide, SF sulfuryl fluoride. DB (debarked) and KD (kiln-dried) are older or separate marks. For reuse, pick HT and avoid MB.
- GuidesFood-grade pallets: what the term means and how to specify oneThere is no FDA certification for a food-grade pallet. The term means a clean, dry, uncontaminated pallet: new or top-grade wood, kiln-dried and heat-treated (never methyl bromide), or virgin food-contact plastic. FSMA requires transport equipment that will not make food unsafe.
- GuidesPallet mold: causes, prevention and what to do with moldy palletsPallet mold grows when wood stays above about 20% moisture in warm, still air: green pallets in containers, wrapped loads or covered yards. The fix is dry wood: specify kiln-dried pallets (19% or less), store them dry and ventilated, and check moisture before loading. HT alone does not prevent mold.
Last reviewed 2026-09-24. 1,319 words.