Reaction to fire classes: from A1 to F

The scale

A1 — does not contribute to fire. Mineral wool, concrete, steel, glass.

A2 — effectively non-combustible, with negligible organic content.

B, C, D, E — increasing contribution to fire. B is still limited contribution; E only demonstrates short resistance to a small flame.

F — unclassified, or not meeting E.

The additional markings

Smoke production: s1, s2, s3

Most fire casualties are caused not by flame but by smoke, and smoke also makes escape impossible. s1 means the least smoke. In a light gauge steel build-up this matters because the cavities of the structure can act as smoke paths.

Flaming droplets: d0, d1, d2

This describes whether burning droplets or particles fall from the material. d0 means they do not. On escape routes and facades this is a critical property: falling burning material starts a new fire lower down.

What this means in a build-up

A light gauge steel wall or floor build-up contains many materials side by side, and not all of them are asked for the same thing:

• The lining protecting the structure is usually a high-class, fire resisting board, because it holds the heat back from the section.
• The insulation class matters most where the regulation sets a requirement for the facade or for cavities — this decides whether mineral wool or an organic foam insulation can be considered.
• Membranes and bonded layers are low in mass, but their smoke production is not zero.

What the class alone is not enough for

Verifying the fire resistance of a structure. Even if every layer is A1, the wall will not automatically be REI 60 — load-bearing capacity depends on the heating of the section, not on the combustibility of the layers. On the relationship between the two: fire classification.

The point

The material class says what the material adds to the fire. The structure still has to survive the required time — the two work together, they do not replace each other.