Group B plastics do not release as much heat as Group A when burning, but they produce a heavier fire than cellulosic material. NFPA 13 therefore treats Group B plastic products as Class IV commodities.
Quick reference
| Item | Value |
|---|---|
| Plastics group | Group B |
| Treated as | Class IV commodity |
| Main materials | Nylon, silicone rubber, chloroprene, cellulosics, ECTFE/ETFE/FEP, unexpanded natural rubber |
| FM Global DS 8-1 | Generally treated at Class 4 level; confirm in DS 8-1 |
| Typical protection | Class IV criteria: CMDA, CMSA or ESFR; in-rack where needed |
What it is
Group B covers plastics and elastomers with a moderate heat release. The NFPA 13 list mainly includes cellulosics (cellulose acetate, cellulose acetate butyrate, ethyl cellulose), chloroprene rubber (neoprene), some fluoroplastics (ECTFE, ETFE, FEP), unexpanded natural rubber, nylon (nylon 6, nylon 6/6) and silicone rubber. Products made partly or wholly of these materials are protected as Class IV commodities.
Typical examples
- Nylon rope, cord, fabric and hosiery
- Silicone seals, hoses and kitchenware
- Neoprene (chloroprene) gaskets and wetsuits
- Natural rubber products (unexpanded)
- Cellulose acetate products (e.g. spectacle frame stock, some films and fibres)
How packaging and plastics change the class
The class of Group B comes from the product itself, but the packaging must also be checked. If a Group B product is packed in Group A plastic (EPS foam, PE totes), the Group A share may pass the threshold and the commodity is then treated as Group A. A different form of the same material can change the group too: natural rubber is Group B unexpanded but Group A when expanded (sponge). With fluoroplastics the type matters; PTFE and PCTFE are Group C, while ECTFE, ETFE and FEP are Group B.
Protection approach
Because Group B products are protected to Class IV criteria, the approach is the same as on the Class IV page: CMDA at moderate heights, CMSA or ESFR on tall racks, and in-rack sprinklers where the rack layout requires them. What matters is confirming from material data (technical sheet, safety data sheet) that the product really is Group B; trade names rarely show the polymer type.
FM Global equivalent
FM Global DS 8-1 classifies plastics with its own approach and generally treats materials corresponding to Group B at Class 4 level. The match is not guaranteed for every product; on an FM-approved project, verify against the DS 8-1 tables.
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
- Counting nylon as Group A on a ‘plastic means Group A’ assumption (unnecessary cost), or leaving nylon-blend goods at Class III.
- Taking the expanded (sponge) form of natural rubber to be Group B.
- Ignoring the Group A plastic packaging of a Group B product.
- Putting all fluoroplastics in the same group.
- Guessing the material from the trade name.
Frequently Asked Questions
Which plastics group is nylon in?
Nylon 6 and nylon 6/6 are Group B plastics. Nylon products are protected as Class IV commodities.
Is silicone rubber Group A?
No, silicone rubber is Group B. If it is packed in Group A plastic packaging, the overall assessment of the commodity may change.
Why are Group B plastics treated as Class IV?
Their heat release is lower than Group A but higher than cellulosic material. NFPA 13 meets this middle level with Class IV protection criteria.
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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 8-1). 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.