GENERIC COMMODITY CLASSIFICATION

The National Fire Protection Association Standard 231 (1998) for General Storage is based on a generic classification system involving seven categories of commodities. The seven categories in NFPA 230 (1999) and in the Factory Mutual Commodity Classification Data Sheet 8-1 (1998) are Classes I, II, III, and IV, and Group A, B, and C Plastics. There is significant overlap between Class III and Group C plastics, and between Class IV and Group B plastics. Class I commodities are the least flammable, while Group A plastics are considered to be the most flammable class of general storage. There are also numerous categories for special commodities discussed in Chapters 6, 7, and 8.

Table 5.7 summarizes the classification definitions for Class I, II, III, and IV commodities. A Class I commodity is a noncombustible product in a container of ordinary combustibility, such as an ordinary cardboard carton. Examples of Class I products include glass bottles either empty

Table 5.7. Generic commodity classification in NFPA 230

Class Product Packaging Plastic content

I Noncombustible None; on pallets. Single wall carton, or paper wrap.

Negligible II Noncombustible Multi-wall carton, or wood

crate or wood box.

Either Group B or an appreciable amount of Group A as defined for product.

or filled with nonflammable liquids, metal pots and pans, bags of cement, and ceramic products without any packing material.

A Class II commodity is a Class I product in a slatted wooden crate, a solid wood box, or a multiple thickness corrugated carton. Examples of Class II commodities include beer or wine in (up to 20% alcohol) in wood crates or barrels, lightbulbs in multiple corrugated containers, and large appliances such as washing machines in triwall cardboard cartons.

A NFPA 230 Class III commodity consists of a combustible product with a negligible amount of Group A or Group B plastics (Table 5.8) in either the product or the packaging. Examples include shoes, books, cotton or wool clothing, wood cabinets or furniture (with only a negligible amount of plastic padding), combustible food products, and Group C plastic products such as polyvinyl chloride insulated cable on metal or wood reels.

A NFPA 230 Class IV commodity is defined either as a Class I, II, or III product containing an appreciable amount of Group A plastics in an ordinary cardboard carton, or a Class I, II, or III product in cartons with Group A plastic packaging materials, or a Group B plastic product in a cardboard carton. The NFPA 230 and Factory Mutual definition of an appreciable amount of Group A plastic is that a pallet load of Class IV commodity (including the pallet) should not contain more than 25% by volume of expanded (i.e. foamed) plastic, or more than 15% by weight of unexpanded plastic.

Examples of Class IV commodities cited in NFPA 230 include fiber glass insulation rolls, empty PET beverage bottles in cartons, pharmaceuticals (pills) in cartoned plastic bottles, wood furniture with plastic coverings, wax-coated paper cups and plates, and electrical wire on plastic spools. NFPA 230 also defines a free flowing Group A plastic, comprised of pellets, powder, or flakes, as a Class IV commodity because the free flowing bulk plastic tends to flow out of the container and into the flue space where it can have a smothering effect on the fire.

The Group A, B, and C classification system for plastics is based on the recognition that the flammability properties of plastics and other polymers varies from almost negligible (as in polyte-trafluoroethylene) to substantially more severe than cellulosic materials. Examples of Group A, B,

Table 5.8. Plastic classification examples in NFPA 230 (data from Tewarson, 1995)

Polymer Heat of combustion

Fiberglass Reinforced Plastic 12.9 – 26.0 1.4 – 6.4

Polycarbonate 29.7 2.1

Polyethylene 43.6 1.8(LD), 2.3 (HD)

Polymethyl Methacrylate (PMMA) 25.2 1.6

Polypropylene 43.4 2.0

Polystyrene 39.9 1.3 – 1.9

Polyurethane Foam 23–28 1.2 – 2.7

Group B Plastics

Polyvinyl Chloride (PVC, rigid) 16.4 2.5

Urea Formaldehyde 14.6 –

and C plastics as specified in NFPA 230 are listed in Table 5.8. Heats of complete combustion and effective heats of gasification are also listed in Table 5.8. The corresponding values for cellulose are a heat of combustion of 16.1 kJ/g (7000 Btu/lb) and a heat of gasification for corrugated paper of 2.2 kJ/g or 1000 Btu/lb (from Table 3 – 4.4 of the SFPE Handbook, 1995). According to the data listed in Table 5.8, Group A and B plastics generally have heats of combustion significantly higher than cellulose/paper, while Group C plastics have heats of combustion comparable or significantly less than cellulosic materials. The data also shows that there can be wide variations for certain generic polymers.

The distinction between Group A and Group B plastics is different in NFPA 230 than in Fac-tory Mutual Data Sheet 8-1. Several of the NFPA 230 Group A plastics are considered to be examples of Group B plastics in Factory Mutual Data Sheet 8-0S. These include polycarbonate, polyethylene, polypropylene, and thermosetting polyesters. The Group A, B, and C plastics list-ings in NFPA 230 are apparently based on the original series of small-scale and large-scale plastic commodity fire tests described in Sections 5.4.3 and 5.4.4. The groupings in Factory Mutual Data Sheet 8-1 are based on material heats of combustion and horizontal flame spread rates as well as various sprinklered fire tests. Factory Mutual Research Corporation maintains a computer database of heats of combustion and flame spread rates of commodity samples submitted for classification. The listing of examples of commodity classifications in NFPA 230 has increased significantly in recent editions, but there are still ambiguities, particularly with regard to the use of various types of flame retardants and reformulated polymers.

The Class I, II, III, IV and Group A, B, C classification implicitly assume that the commodity is stored on a wood pallet. If a plastic pallet is used, NFPA 230 and NFPA 13 require that the classification be increased to the next higher (more challenging) classification unless the plastic pallet has been shown to be equivalent to a wood pallet through testing and corresponding certification. The type of testing conducted for this certification is equivalent to the Commodity Classification tests described in Section 5.4.3.

According to laboratory flammability data (Section 5.4.2), the steady-state burning rate per unit horizontal area is proportional to the ratio of the heat of combustion to the heat of gasification.

Values of this ratio calculated from the data for the various polymers in Table 5.8 are listed in Table 5.9.

The ratios listed in Table 5.9 suggest that a possible demarcation between Group A, B, and C plastics might be set at ratios over 20, between 10 and 20, and under 10. However, the fact that the range of ratios shown for polyurethane foam is from under 10 to over 20 indicates that some

Table 5.9. Ratios of heat of combustion to heat of gasification

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