The direct answer: BS EN 13501-1 Class B-s2,d0 describes a product’s reaction to fire. The three parts report its contribution to fire, smoke production and flaming droplets or particles.
It is one complete classification. Writing only “Class B” leaves out the smoke and droplet classifications and may not describe the evidence accurately.
01 · Reading the classification
What do B, s2 and d0 mean?
The main reaction-to-fire class. Class B indicates very limited contribution to fire under the relevant test and classification criteria.
The smoke classification. s2 is an intermediate level: it is not the lowest-smoke s1 classification, but it is more demanding than s3.
The flaming-droplet classification. d0 means no flaming droplets or particles.
The suffixes matter. For example, B-s1,d0 and B-s2,d0 share the same main B class and d0 result, but their smoke classifications are different.
The current classification framework is explained in Approved Document B.
02 · Avoiding common confusion
What does B-s2,d0 not mean?
Class 0 was a National designation associated with BS 476 test routes. B-s2,d0 is a BS EN 13501-1 classification and is not an automatic conversion from Class 0.
B-s2,d0 concerns reaction to fire. A time-based rating concerns the fire resistance of a tested construction or building element.
If a specification asks for B-s1,d0, evidence for B-s2,d0 should not be relabelled as s1. The exact letters and suffixes on the classification documentation matter.
For more detail about the older terminology, read Is BS 476 Class 0 still valid for wood?
03 · The tested system
What does the classification apply to?
A reaction-to-fire result applies within the field of application supported by the test and classification evidence. It should not automatically be extended to every timber species, thickness, profile, treatment quantity or installation.
The supporting evidence may define
- Timber species, density and thickness
- Profile and surface condition
- Treatment product and application quantity
- Substrate, air gap and fixing arrangement
- Orientation and intended end-use
- Any maintenance or re-treatment requirements
UK Government guidance similarly warns that reaction-to-fire performance can change with the product’s form, orientation, substrate, fixings and other parts of the tested configuration.
Source: Approved Document B fire-safety FAQs — classification and field of application.
04 · Treatment documentation
What documents support treated timber?
For a treatment system classified to B-s2,d0, the manufacturer’s classification documentation sets out the tested result and its conditions. A treatment certificate records the site, timber, product and completed application.
Both documents should be kept with the project’s fire-safety records. The treatment certificate records the work completed; the manufacturer’s documentation provides the supporting classification evidence for the treatment system.
05 · Common questions
B-s2,d0 questions
What does B-s2,d0 mean?+
B-s2,d0 is a reaction-to-fire classification under BS EN 13501-1. B describes the contribution to fire, s2 is the smoke-production classification and d0 means no flaming droplets or particles.
Is B-s2,d0 the same as B-s1,d0?+
No. Both have reaction class B and droplet class d0, but s1 is the more demanding smoke classification. B-s2,d0 has an s2 smoke classification.
Is B-s2,d0 the same as Class 0?+
No. Class 0 was a National designation using BS 476 test routes. B-s2,d0 is a European reaction-to-fire classification under BS EN 13501-1, and one must not be presented as an automatic conversion of the other.
Does B-s2,d0 provide 30 or 60 minutes of fire protection?+
No. B-s2,d0 concerns reaction to fire. Thirty- and sixty-minute ratings concern fire resistance of a tested construction or building element.
Does a B-s2,d0 result apply to every timber product?+
No. The classification applies within the field of application supported by the test and classification evidence, including the relevant product, treatment and installation conditions.