In Class III the product itself burns: goods made of wood, paper, natural-fibre cloth or Group C plastics. A large share of general warehouses fall into this class.
Quick reference
| Item | Value |
|---|---|
| NFPA 13 class | Class III |
| Product | Wood, paper, natural fibre, Group C plastics |
| Group A/B plastic limit | Up to 5% by weight or volume |
| FM Global DS 8-1 | Class 3 (definitions not identical) |
| Typical protection | CMDA, CMSA or ESFR; in-rack for tall racks and solid shelves |
What it is
A Class III commodity is a product made of wood, paper, natural-fibre cloth or Group C plastics, with or without cartons, boxes or crates, and with or without pallets. A limited amount of Group A or Group B plastics, up to 5% by weight or by volume, may be present in the product or its packaging. Cellulosic materials ignite easily but release less energy per unit mass than plastics, and they absorb sprinkler water well.
Typical examples
- Books, magazines, paper products and boxed stationery
- Wood furniture without plastic upholstery
- Cotton, wool and linen clothing and textiles
- Dry food in cartons (flour, cereal, pasta)
- Leather goods
- Products of Group C plastics (e.g. rigid PVC pipe and profiles)
How packaging and plastics change the class
The weak point of Class III is the 5% threshold. Add foam corner guards to boxed furniture, plastic wrapping to book cartons or polyester blends to clothing, and the Group A plastic share easily passes the limit, moving the commodity to Class IV. Synthetic fibres such as polyester and nylon are not natural fibres and change the class according to their proportion. Roll paper is assessed as a separate commodity under its own rules; being paper does not make it Class III automatically.
Protection approach
For Class III, CMDA ceiling sprinklers are common up to moderate heights. As height increases, CMSA or ESFR are preferred; where its conditions are met, ESFR often removes the need for in-rack sprinklers. Water absorption by cartoned goods and the tendency of stacks to collapse also matter for post-fire structural loading. As a general rule, Class I–IV commodities stored above 12 ft (3.7 m) are designed to the storage chapters rather than the general hazard classes; confirm the threshold in the edition in force.
FM Global equivalent
In FM Global DS 8-1 the equivalent is mostly Class 3. FM applies its own proportions and examples when assessing plastic content, so a product that is Class III under NFPA may be treated differently by FM. See DS 8-1 commodity classification.
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
- Classing a textile store as Class III because ‘fabric is Class III’ without checking synthetic fibre content.
- Ignoring foam and plastic upholstery on wood furniture.
- Assuming cartoned goods and roll paper are the same class.
- Assessing the 5% limit against the whole warehouse average; it applies per commodity unit (pallet load).
- Not reflecting the extra plastic mailers and void fill that come with a shift to e-commerce.
Frequently Asked Questions
How much plastic can a Class III commodity contain?
Total Group A or Group B plastics in product and packaging must not exceed 5% by weight or volume. Above that the commodity moves to Class IV or higher.
What class is a rigid PVC pipe store?
Rigid (low-plasticiser) PVC is a Group C plastic, and Group C plastics are treated as Class III. Highly plasticised flexible PVC is Group A.
What class is a book warehouse?
Books and paper products are typically Class III. If plastic covers and packaging are significant, the class should be reassessed.
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 8-1). 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.