I would generally support the change to a performance based surface finishes in the BC.
An ultrafast fire is very conservative for the case of flooring <2.2kW/m2 CRF, when you look at the expected ASET times against the tenability criteria (in particular visibility and received radiation) as flooring is not involved in the fire until it is getting towards flashover. Consider the 2 scenarios – fire spread on the flooring (lateral flame spread) in the early stages of the fire, and then widespread fire spread on the flooring once the CRF value is reached from the combined hot layer and direct radiation.
In the modelling I have done, it is reasonably conservative for walls, although this did not look at re-entrant comers where there is re-radiation and increased burning and spread and it certainly varies by building height, materials etc. In B-risk, the worst case is in a corner and slightly away from the walls so you get an axisymetric plume with rapid ignition of 2 walls for the highest entrainment, whcih may not be immediately apparent when unless you understand the plume behavior. The assumed burner width is critical to the result.
The basis of the Marae allowances (double the width and half the travel distances in C/AS4) are flaky to say the least. it is based on a BRANZ paper from the 1990s, with some fire testing showing that lining your marae with kindling was a fire hazard… It is based on a 15s premovement time and a 3.2m average ceiling height. The 2 determinations on timber linings used this as the basis for saying timber was ok - evn through the room size, height was different and they had excess door width. If you model them and apply minimum widths, they failed…
It doesn’t appear that any consideration is given to fire spread by direct flame impingement. As the upper part of the wall, and the ceiling in particular is in the hot layer and in direct contact with flames extending along the ceiling, giving much faster fire spread combined with falling or melting material.
I believe the Stardust Disco fire is an example of this, as is the Summerland fire with falling droplets from acrylic roofing.
A few comments
The exclusions do not apply to detached dwellings, outbuildings etc. What about inside household units such as apartments (but not their exitways, common areas, etc)? as it is currently written, anyone doing interior decorating or renovation of an apartment household unit would need to meet the surface finish requirements, which is practically and socially impractical and unenforceable.
I suggest that household units (purpose group SR) are excluded but only within the private household unit but not common areas, exit ways, other purpose groups or transient accommodation such as hotels.
Where do green walls (real or artificial) fit in this definition? These has a permanent frame attached to the wall with real or artificial plants growing up them. Some of the artificial plants have Euroclasses tests (e.g. https://www.evergreenwalls.com.au/#home) which equate to Group 2.
“f) structural timber building elements constructed using solid wood, glulam, laminated
veneer lumber, cross-laminated timber, of no more than 25% of the total wall area”
Does this also apply to timber formwork of rib and infill floors, or other timber panels (such as acoustic panels in theatres) if they are also <25% of the ceiling area, or is the intent that any timber on the ceiling is not allowed (unless group 3 is allowed)? A compromise may be to include it in the allowances for roof lighting as many of these panels are group 3 as well.