Short answer: Under BYKHY Annex 2/A, class A2 materials do not contribute significantly to the fire load and fire growth under fully developed fire conditions. s1 is the smoke production class meeting stricter criteria than s2. d0 means no flaming droplets or particles. In Annex 2/Ç this combination is given as the equivalent of a material of limited combustibility.

The code A2-s1,d0 carries three pieces of information at once. A2 says the material does not contribute significantly to fire growth, s1 that smoke production is in the strictest band, and d0 that no flaming droplets form. Annex 2/Ç of the Turkish Regulation on Fire Protection of Buildings (BYKHY) gives this combination directly as the equivalent of a material of limited combustibility.

Where the Regulation defines combustibility

BYKHY Article 29(5) states that the relevant regulations and standards govern the determination of the reaction-to-fire classes of construction materials. The tables showing the classes are gathered by Article 29(6) into four annexes.

Fire resistance is a separate subject, left to Article 29(7) and Annex 3: Annex 3/A gives the fire resistance symbols of building elements, Annex 3/B the resistance periods, and Annex 3/C the periods by building occupancy class. In Annex 3/A, R denotes load-bearing capacity, E integrity, I insulation and W radiation; in the same annex M stands for mechanical resistance, C for self-closing and S for smoke leakage. In short: A2-s1,d0 is the reaction of a material, REI 90 is the resistance of a building element. The period required for a boiler room enclosure is on the resistance side; for detail see the boiler room 120-minute rule article.

A1 to F: what Annex 2/A says

Class BYKHY Annex 2/A definition
A1 Does not contribute to fire at any stage of burning, including fully developed fire; it is deemed to satisfy all the properties of the lower classes
A2 Meets the class B criteria to TS EN 13823; in addition, under fully developed fire conditions it does not contribute significantly to the fire load and fire growth
B Meets stricter requirements in addition to the class C criteria
C Meets stricter requirements in addition to the class D criteria; lateral flame spread under thermal attack by a single burning item remains limited
D Meets the class E criteria and resists a small flame attack for a long period; withstands thermal attack by a single burning item with limited heat release
E Resists a small flame attack without significant flame spread for a short period
F Material whose fire performance has not been determined and which is not classified between A1 and E

Annex 2/A also defines the smoke and droplet suffixes. Smoke: s3 is the class with no limit on smoke production, s2 the class in which total smoke production is limited as well as its rate of increase, and s1 the class meeting stricter criteria than s2. Flaming droplets and particles: d2 means no limit, d1 means no droplets or particles for longer than a set time, and d0 means no flaming droplets or particles at all.

Floorings are classified under Annex 2/B in a separate family: A1fl, A2fl, Bfl, Cfl, Dfl, Efl, Ffl. This family has only two smoke levels; in Annex 2/B s2 means no limit and s1 means total smoke production is limited. Cfl-s1 written on a floor finish's data sheet is not a typo but a class from the correct family.

Annex 2/C lists the materials deemed A1 and A1fl without testing. The list includes concrete and precast reinforced concrete products, aerated concrete units, cement and fibre cement, mineral wool, expanded clay, expanded perlite and vermiculite, cellular glass, and metals such as iron, steel, stainless steel, copper, zinc, aluminium and lead. Asking for a separate test report for a material on this list is an unnecessary demand; an A1 claim for a product not on the list, on the other hand, cannot be accepted without documentation.

Limited combustibility, low flammability: the Annex 2/Ç mapping

The articles of the Regulation do not use codes but Turkish terms: non-combustible (hiç yanmaz), limited combustibility (zor yanıcı), low flammability (zor alevlenici), normal flammability (normal alevlenici) and high flammability (kolay alevlenici). The TS EN 13501-1 equivalents of these terms are given in Annex 2/Ç. This is the table to use when writing a specification.

Combustibility property Annex 2/Ç equivalent (construction materials other than floorings)
Non-combustible A1
Limited combustibility A2-s1,d0
Low flammability B,C-s1,d0; A2-s2,d0; A2,B,C-s3,d0; A2,B,C-s1,d1; A2,B,C-s1,d2; at least A2,B,C-s3,d2
Normal flammability D-s1,d0; D-s2,d0; D-s3,d0; E; D-s1,d2; D-s2,d2; D-s3,d2; at least E-d2
High flammability F

Table note: In the Annex 2/Ç table of the current consolidated text (including the amendment of OG 01/07/2025-32943), the first row of the low flammability group is B,C-s1,d0; classes B-s1,d0 and C-s1,d0 are equivalent to low flammability.

For floorings Annex 2/Ç gives a separate table: non-combustible A1fl, limited combustibility A2fl-s1, low flammability Bfl-s1 and at least Cfl-s1, normal flammability the rows from A2fl-s2 to Efl, high flammability Ffl.

The first footnote of Annex 2/Ç carries an important warning: for construction materials with the combustibility classes given in TS 1263 to be considered equivalent to the TS EN 13501-1 classes, those materials must meet the test standard requirements for the relevant class specified in TS EN 13501-1. In other words, a certificate based on the old class name does not on its own carry the new class.

What the Regulation asks for each surface

The combustibility requirement is not in a single article but spread surface by surface.

General prohibition. Under Article 29(2), highly flammable construction materials may not be used in construction; such materials may only be used if converted into a normally flammable material within a composite.

Internal wall linings and internal insulation. Under Article 29(3), internal wall linings and internally applied thermal and acoustic insulation are made of at least normally flammable material, and of at least low-flammability material in high-rise buildings and in places such as cinemas, theatres, conference halls and wedding halls with a capacity of more than 100 people.

Service pipes. Under Article 29(4), in high-rise buildings, service pipes larger than 70 mm in diameter must be of at least low flammability, except branch pipes passing through wet rooms. Where normally flammable soil pipes are used, fire stops providing the same fire resistance as the compartment wall are used at floor penetrations.

Floor and ceiling. Under Article 26(2), floor finishes are at least normally flammable, and at least of low flammability in high-rise buildings. Article 26(3) allows thermal insulation of highly flammable material on a floor only if it is covered by a screed at least 2 cm thick. Under Article 26(4), the ceiling linings and suspended ceiling materials of buildings other than detached houses in detached layout must be at least of low flammability.

Escape routes. Under Article 38(3), no combustible material may be used on the walls, ceiling and floor of escape stairs. The same prohibition applies to fire lobbies through Article 34(2). For the escape route chain as a whole, see the escape routes and stairs article.

Façade and roof. The façade requirement is in Article 27 and the roof requirement in Article 28. Under Article 28(2), the surface or insulation beneath roof coverings must be at least of low flammability.

Compartment integrity and material selection go together; how compartment areas change with occupancy class can be found in the fire compartment areas article. Which approval body a certificate comes from is a separate subject; the differences between TSE, CE, FM, UL and VdS are compared in the certification schemes article.

System certification: not the product, the installed build-up

The Regulation explicitly asks for system certification in two places. Article 26(1) requires that, where the infill of non-precast ribbed slabs is of the normal flammability class, the system formed by the infill together with the ceiling lining be certified by an accredited laboratory as at least of low flammability and with a fire resistance class complying with Annex 3/B, and that the system detail appear in the product's placing-on-the-market documentation. Article 27(2)(a) takes the same approach for thermal insulation systems: the system made up of the insulation material, adhesive, anchors, render mesh and render must be certified by an accredited laboratory.

The logic here can be applied directly on site: the class belongs not to the product but to the installed build-up. A board may have a class on its own, but the system it forms with its adhesive, substrate, mesh and render may behave differently. By asking for system certification in these two places, the Regulation in effect describes a general inspection habit.

Field note

On one project the specification required at least low flammability for the suspended ceiling tiles. At material acceptance the tile's certificate arrived complete. But the acoustic felt laid behind the tiles did not appear in any document; the support system and the felt added a combustible load unrelated to the tile's class. What Article 26(4) asks for directly is the ceiling lining and suspended ceiling material; asking for a class for every layer that goes into that void, however, is what actually carrying out the inspection means.

A second example: in a high-rise building the soil stack was of normally flammable material and larger than 70 mm in diameter. In that case Article 29(4) requires fire stops at floor penetrations rated to the compartment wall's resistance period. The fire stops had not been installed, and there was an attempt to brush the issue aside by debating the pipe's class. Yet the paragraph does not prohibit a normally flammable pipe; it requires a fire stop at the floor penetration if you use one.

The lesson: add a single line to your material acceptance form and write the target Annex 2/Ç code for every product. Writing the term without the code leaves the supplier room for interpretation.

Checklist

FAQ

What does A2-s1,d0 mean?

Under BYKHY Annex 2/A, class A2 materials do not contribute significantly to the fire load and fire growth under fully developed fire conditions. s1 is the smoke production class meeting stricter criteria than s2. d0 means no flaming droplets or particles. In Annex 2/Ç this combination is given as the equivalent of a material of limited combustibility.

Which class does BYKHY mean by "limited combustibility"?

BYKHY Annex 2/Ç gives the limited combustibility equivalent for construction materials other than floorings as A2-s1,d0. The non-combustible equivalent is A1 and the highly flammable equivalent is F. For low flammability and normal flammability, Annex 2/Ç lists more than one code row; all of these rows need to be considered when writing a specification.

Can highly flammable materials be used in a building?

Under BYKHY Article 29(2), for reasons of fire safety, highly flammable construction materials may not be used in construction. Such materials may only be used if converted into a normally flammable material within a composite.

Are reaction-to-fire class and fire resistance the same thing?

No. Reaction-to-fire classes are given in the Annex 2 tables under BYKHY Article 29(6), and fire resistance in the Annex 3 tables under Article 29(7). In Annex 3/A, R denotes load-bearing capacity, E integrity, I insulation and W radiation. A2-s1,d0 is the reaction of a material; REI 90 is the resistance of a building element.

References

This article is for general information. For article numbers, thresholds and exemptions, the current regulation and standard texts published in the Official Gazette govern, and design must be carried out by an authorised engineer.

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Sources & Disclaimer

Sources are listed in the References section at the end of the article. Quotations from the regulation are unofficial English translations of the Turkish text. This article is for general information; for article numbers, thresholds and exemptions, the current regulation and standard texts published in the Official Gazette govern, and design must be carried out by an authorised engineer.