EN 12845 Annex G — Idle Pallet Storage

Stacked empty pallets form a fire chimney — the air gap between every board accelerates the flame, and even sprinkler water struggles to keep up. Annex G sets separate stack limits, separation distances and design densities for timber and plastic pallets.

At a food distribution warehouse, 800 empty timber pallets had been stacked 4 m high, around 24 pallets per stack. The design was OH3, delivering 5 mm/min. Over a closed weekend a spark from an overloaded distribution board ignited the stacks, and flame rose through the 1.5 m gap between two stacks within a minute. The sprinklers operated in 12 s, but the chimney effect dragged the droplets sideways and the flame front reached ceiling level. Within 22 minutes 1800 m² was alight. Annex G limits empty pallet stacks to 1.8 m indoors — the stack was more than twice that.

Why empty pallets are a separate category

Empty pallets form their own class in Annex G because of the stacking hazard: very high fire load per unit volume, extensive air gaps and a pronounced chimney effect. They behave quite differently from loaded pallets, where the goods on top actually slow fire spread. Empty pallets accelerate it.

Indoor stack heights

Pallet type	Max. stack	Design density	Area
Timber (1200 × 800)	1.8 m	10 mm/min	260 m²
Timber	3.0 m	12.5 mm/min plus in-rack	260 m²
Timber	Above 3 m	ESFR K200/K360	12 sprinklers
Plastic (PP/HDPE)	1.2 m	12.5 mm/min	360 m²
Plastic	2.4 m	16.5 mm/min plus in-rack	360 m²
Plastic	Above 2.4 m	ESFR K360 at 5.2 bar	12 sprinklers
Mixed	Worst case	Assessed as plastic	360 m²

Outdoor separation distances

• From the building facade: at least 6 m for timber, 9 m for plastic
• Where the facade is not REI 60: 12 m for timber, 18 m for plastic
• From another pallet stack: at least 8 m
• From the roof eaves: at least 1.8 m
• Stack footprint: no more than 6 × 6 m
• Stack height outdoors: no more than 6 m
• Below windows or rooflights: at least 6 m
• From a fire hydrant: at least 6 m

Field error — pallets accumulating during a seasonal peak

At a logistics facility, pallet stock jumped from 200 to 950 before a holiday shutdown as empty pallets came back from stores. Maintenance stacked them by the door, 2 m from the facade, where the original design assumed 6 m. Over the holiday a spark from the heating system ignited the stack and flame spread to the building because the facade panel had no fire-retardant treatment. Sprinklers could not help — the fire was outside. Empty pallet stock has to be managed, with a separate external area and a distance plan for seasonal peaks.

A specific warning on plastic pallets

PP and HDPE pallets carry three to four times the fire load of a timber pallet. Ignition temperature is low, around 350 °C, flame spreads rapidly, and the material melts and drips. Molten plastic runs onto the tier below and enlarges the fire area. For plastic pallets, Annex G effectively makes ESFR the only practical solution: K360 at 5.2 bar with twelve operating heads suppresses the fire within minutes, whereas the in-rack alternative is complex and difficult to maintain.

Compact versus spaced stacks

• Compact stack: pallets stacked directly on top of each other and tightly arranged — maximum chimney effect
• Spaced stack: 1.2 m of air between stacks — a fire at the base is easier to control, but many more stacks are needed
• Annex G applies stricter height limits to compact stacks
• Spaced stacking can buy one or two extra tiers of height
• In practice floor economics push everyone toward compact stacks, so the design must assume that

Estimating the fire load

A single timber pallet (1200 × 800 × 144 mm, about 25 kg) has a calorific value of roughly 18 MJ/kg, so 450 MJ. A polyethylene pallet at about 22 kg carries 46 MJ/kg, so 1012 MJ — 2.2 times the timber figure. A 200-pallet timber stack holds about 90 000 MJ. That is enough energy to drive a 1500 m² warehouse to 800 °C, and the 60 min sprinkler duration calculation has to be made against that fire load.

Pallets in racks or under mezzanines

Storing empty pallets under a mezzanine or inside racking is particularly dangerous, because ceiling sprinklers cannot reach and water never gets under the goods. The remedies:

• Additional sprinklers beneath the mezzanine, at 2 m spacing
• In-rack sprinklers at 3 m spacing inside the racking
• Stack height beneath a mezzanine limited to 1.2 m
• Rack storage of empty pallets is generally not recommended; an external area is preferable

Comparison with NFPA 13 and FM Global

NFPA 13's idle pallet storage provisions are the detailed counterpart to Annex G. The indoor timber limit of 6 ft (1.8 m) is the same, and the ESFR route allows storage up to about 9.1 m under a ceiling with K200 at 75 psi (5.2 bar). FM Global's idle pallet data sheet is the most comprehensive source, classifying PP, HDPE and PET pallets separately. In Turkey, domestic manufacturers' warehouses tend to follow Annex G while international logistics operators prefer the FM Global data sheet.

Turkish regulation and local practice

BYKHY's provisions on bulk storage contain no specific rule for empty pallets, leaving it open to interpretation under Annex G or NFPA 13. Insurers generally audit against Annex G and the external stock separation distances. In many Turkish organised industrial zones, local fire authority interpretation limits stack height to 1.8 m. Stock management discipline is critical: if pallets delivered to market are not collected back on a regular cycle, the stacks simply grow.

Quick check list

• Pallet type (timber, plastic, mixed) established.
• Stack height within the Annex G table.
• External stock at least 6 m (timber) or 9 m (plastic) from the facade.
• 8 m separation between stacks.
• Stack footprint no more than 6 × 6 m.
• Forklift battery charging at least 8 m away.
• A stock plan exists for seasonal peaks.
• ESFR designed where plastic pallets exceed 2.4 m.
• Pallets under a mezzanine limited to 1.2 m.
• No smoking, heaters or other ignition sources.

Frequently Asked Questions

How high may empty timber pallets be stacked indoors?

1.8 m at 10 mm/min. Up to 3 m requires 12.5 mm/min plus in-rack protection, and anything above 3 m needs an ESFR design.

Why are plastic pallets so much worse?

They carry three to four times the fire load of timber, ignite around 350 °C, and melt and drip onto the tier below, enlarging the fire. Above 2.4 m, ESFR is effectively the only practical answer.

What separation is needed for outdoor pallet stacks?

At least 6 m from the facade for timber and 9 m for plastic — doubled where the facade is not REI 60 — plus 8 m between stacks and a footprint no larger than 6 × 6 m.

Why do empty pallets burn worse than loaded ones?

Because of the chimney effect. The air gap between every board accelerates flame spread, while the goods on a loaded pallet actually slow it down.

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