Why the commodity class matters
In NFPA 13-2025 storage protection starts with the commodity class (20.2(1)): density, area, sprinkler type and the need for in-rack sprinklers all follow from it. The unit of classification is the individual storage unit; the product, its primary packaging and the pallet are considered together (20.3.1, 20.3.1.1).
The eight-step severity ranking (20.3.1.3)
For the same storage arrangement, from lowest to highest: Class I, Class II, Class III, Class IV, cartoned nonexpanded plastic, cartoned expanded plastic, exposed nonexpanded plastic, exposed expanded plastic. Protection criteria for one step may protect the lower steps in the same list (20.3.1.4).
Thresholds
| Group A share | Cartoned / wooden container | Exposed |
|---|---|---|
| Nonexpanded by weight ≤ 5 % | Class III (20.4.3.2) | Class III |
| Nonexpanded by weight > 5 – 15 % | Class IV (20.4.4.1(3)) | Class IV (20.4.4.1(6)) |
| Nonexpanded by weight > 15 % | Nonexpanded Group A (20.4.5.4(1)) | Nonexpanded Group A (20.4.5.4(4)) |
| Expanded by volume ≤ 5 % | Class III (20.4.3.2) | Class III |
| Expanded by volume > 5 – 25 % | Class IV (20.4.4.1(4)) | Nonexpanded Group A (20.4.5.4(5)) |
| Expanded by volume > 25 – 40 % | Nonexpanded Group A (20.4.5.4(2)) | Expanded Group A (20.4.5.3(2)) |
| Expanded by volume > 40 % | Expanded Group A (20.4.5.3(1)) | Expanded Group A |
When solid and foam plastics are mixed, read the class from Figure 20.4.3.3(a) (cartoned) or 20.4.3.3(b) (exposed). On the cartoned chart the Class IV limit is a straight line from 15 % solid plastic down to 25 % foam; on the exposed chart the Class IV zone exists only up to 5 % foam. Paper-wrapped or encapsulated loads are considered exposed (3.3.74).
Plastic groups and the decision tree
Group B plastics and free-flowing Group A plastics (powder, pellets, flakes) are protected as Class IV, Group C plastics as Class III (20.4.8.1, 20.4.8.2; Figure 20.4.8). A plastic not named in 20.4.5 is treated as Group A unless testing shows otherwise; plastics are not grouped by heat of combustion (A.20.4). Fire-retardant additives alone do not reduce the class (A.20.4.5).
Plastic pallets
Wood or metal pallets are assumed in classification (20.3.2.1). Unreinforced polypropylene (PP) or high-density polyethylene (HDPE) pallets raise Class I–IV by one class, reinforced pallets by two; on a reinforced pallet Class IV becomes cartoned nonexpanded Group A (20.3.2.2.1.1, 20.3.2.2.2.1). A pallet without a permanent marking or manufacturer's certification is assumed reinforced (20.3.2.2.2.2). On plastic pallets other than PP/HDPE, Class I–III is set by testing or raised two classes, and Class IV becomes cartoned nonexpanded Group A (20.3.2.4). Pallets do not raise Group A commodities (20.3.2.2.3). With ceiling-only protection and spray sprinklers of at least K-16.8 (240) the PP/HDPE increases do not apply (20.3.2.2.4).
Frequently Asked Questions
How much plastic can a Class III commodity contain?
5 percent or less by weight of nonexpanded, or 5 percent or less by volume of expanded, Group A or Group B plastic (NFPA 13-2025 20.4.3.2). Exactly 5 % is still Class III; above it a cartoned commodity becomes Class IV.
Why do cartoned and exposed commodities classify differently?
Exposed Group A plastic moves up faster: more than 5 % by volume of foam makes an exposed commodity nonexpanded Group A (20.4.5.4(5)), while a cartoned one stays Class IV up to 25 % (20.4.4.1(4)). Paper-wrapped or encapsulated loads are considered exposed (3.3.74).
How do plastic pallets change the commodity class?
Unreinforced PP/HDPE pallets raise Class I–IV by one class, reinforced or unmarked pallets by two; on a reinforced pallet Class IV becomes cartoned nonexpanded Group A (20.3.2.2.1.1, 20.3.2.2.2.1, 20.3.2.2.2.2). Group A commodities are not raised (20.3.2.2.3); with ceiling-only protection using spray sprinklers of at least K-16.8 (240) the PP/HDPE increase does not apply (20.3.2.2.4).
Which class governs mixed storage?
The highest classified commodity and storage arrangement (20.4.15.2). Limited exception: up to 10 randomly dispersed, non-adjacent pallet loads in an area not exceeding 40,000 ft² (3720 m²) (20.4.15.3).
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