EN 12845 Material Factors M1-M4 and Storage Category: Annex B

The first step of the calculation in warehouse sprinkler design is not the pipe but the commodity. TS EN 12845+A2:2026 classifies the stored goods in two stages: first the material factor (M1-M4), then the category (Category I-IV) after correction for the storage configuration. Source: TS EN 12845+A2:2026, Annex B (normative), Annex C (normative) and Clause 6.3.1.

The logic of the method: Clause B.1

The NOTE to Clause B.1 (TS p.130 / EN p.127) sets the framework: the overall fire hazard of stored goods (defined as the product and its packaging) is a function of the heat release rate (kW), which in turn is a function of the heat of combustion (kJ/kg) and the rate of burning (kg/s). The heat of combustion is determined by the material or mixture of materials in the goods. The rate of burning is determined both by the materials it contains and by the configuration of the material.

The method follows from this: the material is analysed and a material factor is determined. Where necessary, the material factor is modified according to the configuration of the goods in order to determine the category. Where no modification is necessary, the material factor alone determines the category.

Clause 6.3.1 (TS p.36 / EN p.33) requires the flow chart in Figure 2 to be followed in order to determine the required design criteria where stored goods are involved; the NOTE adds that where none of these annexes is exactly applicable and large scale fire test data are available, those data may be used to determine the design criteria.

The four material factors

Clause B.2.1: where the goods consist of a mixture of materials, the material factor is determined using Figure B.1. In Figure B.1 the horizontal axis is the percentage of expanded plastic by volume and the vertical axis the percentage of non-expanded plastic by mass. In the assessment, the stored goods are taken to include all packaging and pallet material, and rubber is assessed in the same way as plastic.

Material Factor 1 (Clause B.2.2): non-combustible products in combustible packaging, and products of low or medium combustibility in combustible or non-combustible packaging. Products with a low plastic content as follows:

• non-expanded plastic content less than 5 per cent by mass (including the pallet),
• expanded plastic content less than 5 per cent by volume.

Examples: metal parts with or without cartons on wooden pallets; powdered foodstuffs in sacks; canned food; non-synthetic fabric; leather goods; wooden products; ceramics in cartons/wooden crates; metal hand tools in carton/wooden packaging; non-combustible liquids in cartoned plastic or glass bottles; large electrical domestic appliances (with little packaging).

Material Factor 2 (Clause B.2.3): goods with a higher energy content than Material Factor 1, for example those containing a greater quantity of plastic as defined in Figure B.1. Examples: wooden or metal furniture with plastic seating surfaces; electrical equipment with plastic parts or packaging; electrical cables on reels or in cartons; synthetic fabrics.

Material Factor 3 (Clause B.2.4): material that is predominantly non-expanded plastic (see Figure B.1) or of similar energy content. Examples: batteries without electrolyte; plastic briefcases; personal computers; non-expanded plastic cups and cutlery.

Material Factor 4 (Clause B.2.5): material that is predominantly expanded plastic (more than 40 per cent by volume) or of similar energy content. Examples: foam mattresses; expanded polystyrene packaging; foam upholstery.

Table B.1: the configuration changes the category

Clause B.3.1 (TS p.132 / EN p.129): once the material factor has been determined, the most appropriate category is determined by reference to the storage configuration in column 1 of Table B.1. Where an appropriate category is also given in Table C.1, the higher of the two values is used.

The NOTE to the table directs the reader to Clauses B.3.2 to B.3.8 for the configuration descriptions.

B.3.2 Exposed plastic container with non-combustible contents: applies only to plastic containers holding non-combustible liquids or solids in direct contact with the container. Category I: containers with non-combustible liquid contents. Category II: small (≤ 50 l) containers with non-combustible solid contents. Category III: large (> 50 l) containers with non-combustible solid contents. NOTE: the non-combustible contents act as a heat sink and reduce the rate of burning of the container; liquids are more effective than solids because they conduct heat more efficiently. A separate NOTE states that this configuration does not apply to metal parts in plastic storage boxes.

B.3.3 Exposed plastic surface - non-expanded: where the goods have exposed plastic surfaces forming one or more edges or covering more than 25 per cent of the surface area, the category shall be raised to III or IV. Examples: metal parts in PVC storage boxes; shrink-wrapped canned food. For polypropylene and polyethylene storage boxes, see Clause G.8.

B.3.4 Exposed plastic surface - expanded: exposed expanded plastics are more onerous than plastics that are not exposed; they shall be treated as Category IV.

B.3.5 Open structure: materials of a very open structure generally present a higher hazard than those of a closed structure; a high surface area and easy air access promote rapid burning. The standard's own example summarizes the method: cardboard is Material Factor 1; as flat sheet it is Category I; as erected empty boxes it is Category II (because air reaches it easily); as vertically stacked rolls it becomes Category III or higher (Special Risk) depending on the storage method (tight stacking, banded or unbanded).

B.3.6 Solid block material: materials in solid block form have a low surface area to volume ratio, which reduces the rate of burning and allows a reduction in category. Example: solid rubber blocks, vinyl floor tiles in block stacking. NOTE: this configuration does not apply to blocks of expanded plastic (Category IV).

B.3.7 Granular or powder material: with the exception of expanded plastics, granular materials that spill during a fire tend to smother the fire and are less hazardous than their bulk material equivalents. Example: injection moulding granules stored in cardboard boxes. NOTE 2 is an important exception: this configuration does not apply to rack storage.

B.3.8 No special configuration: goods having none of the characteristics above, for example cartoned goods.

Annex C: from the product name to the category

Annex C (normative, TS p.135-138 / EN p.132-135) gives an alphabetical list of products. The scope sentence of Table C.1: this table shall be used to determine the category of stored products where the packaging (palletized or not) is no more hazardous than a cardboard box or a single layer of corrugated board wrapping.

A few rows showing how the list works:

The fact that the same product appears in two different categories depending on how it is stored (paper rolls horizontal III, vertical IV) is the configuration logic of Annex B carried through into Annex C.

From the category to the design criteria

The category alone does not give a density; the standard ties the density to the triple of category + configuration + stacking height.

The OH limit, Table 1 (Clause 6.2.3, TS p.35 / EN p.32): storage under OH protection is permitted only on three conditions: the protection throughout the room shall be designed to at least OH3; the maximum stacking heights in Table 1 shall not be exceeded; and the maximum storage area of a single block shall not exceed 50 m², with a clearance of at least 2.4 m around the block.

Footnote a to Table 1: where the stacking heights exceed the values in the table, HHS protection is used (see Clause 6.2.4.2 and Clause 7.2). Footnote b: ST6 storage is limited to gondola shelving of 1.2 m total width with a solid central bulkhead extending from the base to the top of the gondola; all other ST6 storage is protected to HHS protection.

The HHS side: Clause 6.2.4.2 (TS p.35 / EN p.32) divides HHS into four categories: HHS1 (Category I), HHS2 (Category II), HHS3 (Category III), HHS4 (Category IV). The density is read from Table 4 (roof/ceiling protection only, TS p.41 / EN p.38) and Table 5 (ceiling together with in-rack sprinklers, TS p.42 / EN p.39). The structure of Table 4 shows that the density does not depend on the category alone: in ST1 free standing stacking, Category I corresponds to 5.3 m at 7.5 mm/min, 6.5 m at 10.0 mm/min and 7.6 m at 12.5 mm/min (over an area of 260 m²); in the same rows the corresponding values for Category IV are 1.6 / 2.0 / 2.3 m. There is no table in the standard giving a single density per category.

K-factor, Table 37a (TS p.107 / EN p.104):

These four are the K-factors defined in EN 12845-1: 57, 80, 115 and 160. Larger K-factors (K200 and above) fall within the ESFR and CMSA scope of EN 12845-2:2024, not of TS EN 12845+A2:2026.

The intersection with Annex G

Some commodities are taken outside the Annex B/C chain and tied directly to Annex G:

• Clause G.8.2 (TS p.154 / EN p.151): polypropylene and polyethylene storage containers shall be classified as HHS Category IV.
• Table G.5 and Table G.6 (TS p.152-153 / EN p.149-150): empty pallets. Timber and cellulosic pallets, and non-expanded high density polyethylene pallets with solid platforms, are protected as Category IV in rack storage; for all other plastic pallets, in-rack protection is provided to Category IV, including one level above the topmost storage level, with K = 115 and a minimum operating pressure of 3 bar, and the ceiling requirement is 25 mm/min over 300 m².
• Clause G.7.2 (TS p.154 / EN p.151): in rack storage of non-woven synthetic fabric, in-rack sprinklers are used to Category IV requirements and the ceiling sprinklers provide at least 12.5 mm/min over 260 m².

Field note: the most frequently overlooked sentence in Annex B is the "higher of the two values" rule in B.3.1; even where a product appears as Category II in Annex C, if its packaging forms an exposed plastic surface Table B.1 moves it to III, and III is what governs.

Frequently Asked Questions

How is the material factor determined in EN 12845?

Clause B.2.1 (TS p.130 / EN p.127): where the goods consist of a mixture of materials, the material factor is determined using Figure B.1. In the assessment, the stored goods are taken to include all packaging and pallet material, and rubber is assessed in the same way as plastic. The M1 limit is given in Clause B.2.2: less than 5 per cent non-expanded plastic by mass (including the pallet) and less than 5 per cent expanded plastic by volume. M4, under Clause B.2.5, is material that is predominantly expanded plastic, more than 40 per cent by volume, or material of similar energy content.

How do you get from the material factor to the category?

Clause B.3.1 (TS p.132 / EN p.129): once the material factor has been determined, the most appropriate category is found by reference to the storage configuration in column 1 of Table B.1. Where an appropriate category is also given in Table C.1, the higher of the two values is used.

Can the same material factor give different categories?

Yes. Table B.1 (TS p.132 / EN p.129) gives the category at the intersection of the material factor and the storage configuration. For example, goods with Material Factor 1 are Category I where there is no special configuration, Category II in an open structure, Category III with an exposed non-expanded plastic surface, and Category IV with an exposed expanded plastic surface.

How does the category limit the storage height?

Table 1 (Clause 6.2.3, TS p.35 / EN p.32) gives the maximum stacking heights for OH3 protection: in free standing or block stacking (ST1), Category I 4.0 m, Category II 3.0 m, Category III 2.1 m, Category IV 1.2 m; in configurations ST2-ST6, 3.5 / 2.6 / 1.7 / 1.2 m respectively. Where these values are exceeded, HHS protection is used.

Which K-factors are used for HHS ceiling sprinklers?

Table 37a (TS p.107 / EN p.104): for HHP and HHS ceiling or roof sprinklers, conventional or spray types with K 80, 115 or 160 at design densities of 10 mm/min and below, and K 115 or 160 above 10 mm/min. For HHS intermediate (in-rack) sprinklers, conventional, spray and flat spray types with K 80 or 115.

References

• TS EN 12845+A2:2026 Clause 6.2.3, Table 1, Clause 6.2.4.2 (TS p.34-35 / EN p.31-32)
• TS EN 12845+A2:2026 Clause 6.3.1, Figure 2 (TS p.36 / EN p.33)
• TS EN 12845+A2:2026 Table 4 (TS p.41 / EN p.38), Table 5 (TS p.42 / EN p.39)
• TS EN 12845+A2:2026 Table 37a (TS p.107 / EN p.104)
• TS EN 12845+A2:2026 Clauses B.1, B.2.1, B.2.2 (TS p.130 / EN p.127)
• TS EN 12845+A2:2026 Clause B.2.3, Figure B.1 (TS p.131 / EN p.128), Clauses B.2.4, B.2.5 (TS p.132 / EN p.129)
• TS EN 12845+A2:2026 Clause B.3.1, Table B.1 (TS p.132 / EN p.129)
• TS EN 12845+A2:2026 Clauses B.3.2-B.3.5 (TS p.133 / EN p.130), Clauses B.3.6-B.3.8 (TS p.134 / EN p.131)
• TS EN 12845+A2:2026 Annex C, Table C.1 (TS p.135-138 / EN p.132-135)
• TS EN 12845+A2:2026 Table G.5 (TS p.152 / EN p.149), Table G.6 (TS p.153 / EN p.150), Clauses G.7.2 and G.8.2 (TS p.154 / EN p.151)

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