SFPE Discussions

When is a window a wall?

Interested in the views of my most learned colleagues. In an argument with my client regarding a fire wall they’ve decided to fully glaze. This fire wall is protecting a single means of escape safe path, they’ve put in --/60/30sm glazing and I’m arguing it should be --/60/60sm glazing. They’ve pointed to C/AS2 4.16.1 and table 4.2 which permits ‘closures’ …“e.g for passage of …light” to only have --/60/30sm rating.

My argument is that this is missing the intent of C/AS2 and NZBC and an approx 4m long by 3m high fire wall protecting a safe path needs to have a --/60/60sm rating!

C/AS2 4.2.1 is the definitive answer for me (“glazing in fire separations shall be fixed fire resisting glazing having the same FRR values for integrity and insulation as the fire separation”) but seems to contradict 4.16.1?!

Rob
Yes you are correct.

4.16. has the requirements for closures (these are elements that CLOSE a hole in a fire separation i.e. doors and access panels/hatches) .
The fully glazed wall is The fire separation and therefore has to have the fire resistance rating required of the wall.
The lesser insulation rating required of a closure recognises the fact that as it is a closure it is unlikely to have room contents close to it or at least not directly in front of it and therefore a radiating object wont be close to the closure.

Hope this helps

Regards

Nick

Adding to Nick’s comments:
A window is part of a wall, unless it is a vision panel within a doorset.

A wall requiring a 60 minute Life Rating in a building that doesnt have sprinkler protection on both faces of the wall will requires a 60/60/60 if it is load bearing, and -/60/60 if it is not load bearing. A fire separation is defined as having passed the standard fire test for the duration of the rating specified, which by default does not include smoke stopping capability. However; C/AS2 does require fire separations enclosing safepaths to also have smoke stopping capability. Therefore; for a window in a -/60/60sm fire and smoke separation, the glazing also needs to be -/60/60sm. However; NZS4232.2:1998 only tests for integrity not insulation. There is no cited standard in C/AS2 for the insulation test on glazing unless its within a door assembly in which case NZS4520:2010 would be the method of testing. Neither of these standards include tests for smoke stopping capability.

Again assuming the building is not sprinkler protected, a fire door only needs to be rated for integrity for the fire separation that it is within, and the insulation value is only required to be 30 minutes. The standard is NZS4520:2010 which tests for integrity and insulation but not for smoke stopping capability. For vision panels as small as 65,000mm2, the insulation value can be ignored. This is the total area of vision panels per doorset, not the maximum individual area of each vision panel in a door set.

Brilliant, cheers Nick. I always wondered why this allowance for a lowering of the insulation was permitted for a fire door, your comment regarding the burning items not likely to be in front makes perfect sense.

Rob,
I would agree with the people above that using C/AS2 the insulation rating is required.
However if the design is undertaken using C/VM2 the reason for the fire separation would need to be looked at and a lower insulation rating maybe justified (or no insulation rating). If it is for means of escape then C/VM2 would permit egress past a glass screen with the 30 minute insulation rating (refer 3.6.1 g) which address egress past a window or glazed panel, analysis is not required where the insulated glazing has an FRR of not less than -/30/30. (you can also do a calculation if no insulation).

Might want to check out the definition of an external wall and split out the primary from the secondary elements. Regardless of the extent of the glazing it will always be secondary to the elements requiring structural adequacy. Fire separations need both.