EN 12845 Commodity Classification: Material Factors M1 to M4

Whether a product is M1 or M4 decides the difference between 5 and 12.5 mm/min in a warehouse fire. Working through the commodity classification annex from a site perspective.

We took over a sprinkler project for an e-commerce warehouse that had been started on an HHS3 design. The client said "electronics" and the drawings followed. But half the goods arriving on pallets were in PE/PP plastic crates, and some in boxes packed with expanded polystyrene. Going through the products one by one against the classification annex, the design had to move to HHS4 — meaning K200 instead of K115 at ceiling level, 12.5 instead of 7.5 mm/min, and added in-rack sprinklers. The pump and pipe sizes were recalculated. Skipping the commodity annex hits a project in its most expensive place.

The logic: material first, then configuration

EN 12845 sets out a two-step method for categorising stored goods. Total fire load is a function of heat release rate; heat release rate is the heat of combustion (kJ/kg) times the burning rate (kg/s). Material composition determines the heat of combustion. The burning rate is determined by material and configuration. So a material factor (M) is assigned first, then a table converts it, by storage configuration, into a storage category I to IV.

The flow: product plus packaging plus pallet → M1 to M4 → category I to IV → design density and area of operation. Where the alphabetical commodity list in the second annex gives a different category, the higher of the two is used.

The material factors

M1 — low combustibility

Non-combustible goods, or goods of low to medium combustibility, in combustible or non-combustible packaging. Plastic content must be below both thresholds:

• Unexpanded plastic below 5 % by mass, including the pallet,
• Expanded plastic below 5 % by volume.

Typical examples: metal parts in cartons on wooden pallets, powdered food in sacks, canned goods, non-synthetic fabric, leather, timber products, ceramics in cartons or wooden crates, hand tools in card or timber packaging, glass or plastic bottles for non-combustible liquids in cartons, large white goods with little packaging. Concrete block, brick and structural steel products belong here too.

M2 — medium combustibility

Higher energy content than M1, with plastic content above the M1 thresholds. Examples: timber or metal furniture with plastic seating surfaces, electrical equipment with plastic parts or plastic packaging, electrical cable on drums or in cartons, synthetic fabrics. Consumer electronics packed in cartons and paper products with plastic caps fall into this category.

M3 — high combustibility

Predominantly unexpanded plastic, or materials of similar energy content. Examples: batteries without electrolyte, plastic briefcases, personal computer housings, unexpanded plastic cups and cutlery. Rubber goods are treated as plastic in the annex, so in practice they behave in the M3 band.

M4 — highest combustibility

Predominantly expanded plastic (over 40 % by volume), or materials of similar energy content. Examples: foam mattresses, EPS packaging, foam-upholstered furniture. Because the heat release rate of M4 is an order above M1 and M2, the standard points directly at HHS4 and usually at an ESFR or in-rack combination.

The configuration factor

The material class alone is not enough. The same material moves category with package and stacking form. The configuration table divides it into seven classes.

Storage configuration	M1	M2	M3	M4
Open plastic containers, non-combustible contents	I/II/III	I/II/III	I/II/III	IV
Exposed plastic surface — unexpanded	III	III	III	IV
Exposed plastic surface — expanded	IV	IV	IV	IV
Open structure	II	II	III	IV
Solid block material	I	I	II	IV
Granular or powdered material	I	II	II	IV
No special configuration (cartoned)	I	II	III	IV

A few field consequences:

• The carton roll paradox: carton is M1. But a horizontal roll of corrugated board is category III, and a vertical roll category IV. The same product, the same mass; simply turning it raised the density from 5.0 to 7.5 mm/min or more.
• Empty cartons: flat board is category I; the same board assembled into an empty box is category II — an open structure with easy air access.
• Plastic granulate: injection moulding feedstock stays in category II as long as it is in cartons, because in a fire it spills and smothers. That does not extend to rack storage.
• The exposed surface threshold: unexpanded plastic exposed on one or more faces, or over more than 25 % of the surface area, pushes the category to III or IV.
• The PE/PP container exception: polypropylene and polyethylene storage containers count as category IV regardless of contents. You cannot argue "it only holds water"; the design proceeds on IV.

From category to design density

Once the storage category is fixed, the design tables apply. Approximate values for free-standing stacks:

HHS	Typical density (mm/min)	Area of operation (m²)	Suggested K-factor
HHS1 (Cat. I)	7.5	260	K115
HHS2 (Cat. II)	7.5	260	K115 / K160
HHS3 (Cat. III)	10.0	260	K160 / K200
HHS4 (Cat. IV)	12.5 or more, or ESFR	260+	K200 / K240, ESFR K360

Stack height above the OH3 limit — 4.0 m for category I, 1.2 m for category IV — automatically triggers the move to high hazard storage. The same commodity protected as OH3 on low racking can end up as HHS4 purely because the rack height changed.

Plastic sub-categories and the commodity list

The second annex gives an alphabetical product list assigning categories directly. Where a product carries different categories from the two annexes, the higher applies. Some practical rows:

• Adhesives with flammable solvent — category III, special protection.
• Asphalt paper in horizontal rolls — II; vertical rolls — III.
• Candles — III. Their thermal behaviour is like plastic.
• Corrugated board in horizontal rolls — III; vertical — IV.
• Synthetic fabric lying flat — III.
• Cotton bales — II, with a note that the area of operation may need increasing.
• Electrical appliances — I if under 5 % plastic by mass, otherwise III.
• Electrical cable and wire — III, with in-rack protection mandatory in rack storage.

Open plastic containers have a further sub-classification:

• Category I: plastic containers holding non-combustible liquids — a beverage in a plastic bottle, for instance.
• Category II: small containers up to 50 L holding non-combustible solids.
• Category III: containers over 50 L holding non-combustible solids.

Liquid delays burning by carrying heat away from the container wall, so a liquid-filled plastic container sits one step below a solid-filled one. On site the bottles look identical, but the contents change the design category.

Common errors

• Forgetting the pallet. Stored goods means product plus packaging plus pallet. M1 dry food on a plastic pallet can shift to M2 once the pallet is counted. A calculation done assuming timber pallets falls short when the site runs on plastic.
• Not counting expanded plastic packing. EPS corner blocks look small but pass the 40 % volume threshold quickly inside a box — a common trap in consumer electronics warehouses.
• Treating rubber as not plastic. The annex evaluates rubber as plastic. Writing M2 because "rubber is organic" is an error; it behaves as M3.
• Calling PE/PP containers "empty". Even filled with water or inert material, a store of PE drums must be protected as HHS4.
• Ignoring the storage limit within OH. Storage inside an OH area requires at least OH3, a block area under 50 m², at least 2.4 m clear around the block, and height within the table. Otherwise it moves to high hazard storage.
• Taking the lower category when the two annexes disagree. Wrong — the higher is required.

Comparison with NFPA

NFPA 13 commodity classification works on two axes: the product itself (Class I–IV) and its plastic content (Group A/B/C, expanded or unexpanded). EN 12845 works on one axis, multiplying material factor by configuration to produce a single category. An approximate mapping:

• NFPA Class I ≈ EN category I (M1, cartoned).
• NFPA Class II ≈ EN category I–II.
• NFPA Class III (timber, paper, natural fibre, no plastic) ≈ EN category II–III.
• NFPA Class IV (limited Group A plastic) ≈ EN category III.
• NFPA cartoned unexpanded plastic ≈ EN category III–IV.
• NFPA exposed expanded plastic ≈ EN category IV (M4).

Hydraulically, the FM Global storage data sheets sit closer to EN 12845; if you are used to the FM class and plastic group thresholds, this annex will feel natural. But the density, area and K-factor combination differs — do not transfer the numbers directly.

Turkish context

BYKHY refers explicitly to EN 12845 for sprinkler systems. Justifying the category choice through the classification annexes is increasingly standard in municipal permit processes. Logistics warehouses in industrial zones that declare "OH3 is sufficient" get sent back when plastic packing is seen on the pallets. In fire brigade approval reports, the answer to "HHS3 or HHS4" is tied directly to the annex category.

Practical advice: include a commodity classification schedule in the handover file — for each main product group, the packaging type, pallet type, M class, configuration, commodity-list row, selected category and design density. That single page cuts the number of review iterations with insurers and inspectors substantially.

Frequently asked questions

How do I determine a commodity's material factor?

Assess the product as a whole, including packaging and pallet. Below 5 % unexpanded plastic by mass and below 5 % expanded by volume gives M1; higher plastic content gives M2; predominantly unexpanded plastic gives M3; over 40 % expanded plastic by volume gives M4.

Does the M class give the design density directly?

No. The M class is combined with the storage configuration to produce a category from I to IV. Design density and area of operation then follow from that category and the storage arrangement.

Which category do PE and PP containers fall into?

Category IV, regardless of contents. ESFR or in-rack protection is usually mandatory.

Are NFPA Class I–IV and EN category I–IV the same?

The numbering is similar but the content differs. NFPA classifies product and plastic content on two separate axes; the EN category is the resultant of material factor and configuration. They map roughly, but check project by project.

Why does a roll of carton change category?

Carton is M1. A horizontal corrugated roll is category III and a vertical roll category IV, because the exposed surface and air flow raise the burning rate substantially.

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