A stack of idle pallets is one of the heaviest fire loads in a warehouse. Dry timber or plastic, a large surface area and the horizontal gaps between pallets create ideal conditions for a very fast-growing fire.
Quick reference
| Item | Value |
|---|---|
| Wood pallets (idle) | Dedicated criteria; preferably outdoors or in a separate area, on the floor indoors |
| Plastic pallets (idle) | Regarded as more severe than wood, except listed equivalent pallets |
| Idle pallets in racks | Needs special criteria; avoid where possible |
| Plastic pallets carrying goods | Can raise the commodity class |
| FM Global | DS 8-24 Idle Pallet Storage |
| EN 12845 counterpart | Annex G: idle pallet storage |
What it is
NFPA 13 treats idle (empty) pallet storage as a hazard separate from pallets carrying goods, with different criteria for wood and plastic pallets. Plastic pallets are generally regarded as a more severe hazard than wood; however, plastic pallets listed as equivalent to wood on the basis of fire testing may be treated as wood pallets.
Typical examples
- Pallet stacks next to loading docks in distribution centres
- End-of-line pallet stock at production plants
- Pallet repair and hire businesses
- Hygienic plastic pallet stock in food and pharmaceutical warehouses
How packaging and plastics change the class
Pallet material also affects the class of commodities carried on pallets. Under NFPA 13, when Class I–IV commodities are stored on unreinforced polypropylene or high-density polyethylene plastic pallets the class is generally raised by one step, and by two steps on reinforced plastic pallets; there are exceptions for some protection options and for listed pallets. Confirm the detail and exceptions of this rule in the edition in force.
Protection approach
The best answer for idle pallets is to store them outside the main building at a suitable distance, or in a separate fire-resisting area. Where indoor storage is unavoidable, pallets are kept on the floor in stacks of limited height and pile size, and protection criteria are taken from the standard according to pallet type, stack height and ceiling height. Idle pallets in racks, combined with the flue effect of the rack structure, create a very severe fire and require special criteria. ESFR can be used for some idle pallet arrangements; check suitability against the standard.
FM Global equivalent
FM Global covers idle pallet storage in DS 8-24 Idle Pallet Storage; FM's split between wood and plastic pallets and its protection tables are its own. For the EN 12845 approach see EN 12845 Annex G idle pallet storage.
The commodity class depends on what goes into the warehouse today. The commodity and storage arrangement assumed in the design report should be recorded in writing and rechecked whenever operations change. For the overall framework see NFPA 13 commodity classification, and for a quick check on whether ESFR can be used, the ESFR suitability checker.
Common site mistakes
- Leaving idle pallet stacks out of the design because ‘there is no product’.
- Stacking pallets above the design height.
- Switching to plastic pallets in a store designed for wood pallets.
- Storing idle pallets on the upper levels of racks.
- Keeping outdoor pallet stacks close to the building façade and openings.
Frequently Asked Questions
Does an idle wood pallet store need sprinklers?
Yes. Idle pallets create a high fire load, and NFPA 13 gives specific protection criteria for them based on pallet type and stack height.
Are plastic pallets more hazardous than wood?
Generally yes; plastic pallets are treated as a more severe hazard. Listed plastic pallets shown by testing to be equivalent to wood may be treated as wood.
Can idle pallets be stored in racks?
It needs special criteria and should be avoided where possible because the rack structure intensifies the fire. If unavoidable, protection must be designed separately to the relevant criteria of the standard.
SprinkCalc — Fire Sprinkler Design Across Three Standards
SprinkCalc covers hazard classification, design density and area, K-factor selection, water demand and hydraulic calculations for NFPA 13, FM Global and BS EN 12845 in a single iOS app, and exports a professional PDF report.
Download SprinkCalc on the App StoreNFPA 13, Standard for the Installation of Sprinkler Systems (current edition) · FM Global Property Loss Prevention Data Sheets (FM Global DS 8-24). This page summarises the definitions in our own words; for design densities, areas and height limits the edition in force and the decision of the authority having jurisdiction govern.