C/AS2 has a restriction within the definition of risk group WB - “Factories, processing and manufacturing plants (excluding foamed plastics)…”
I find the intent of this comment unclear. My default interpretation is that this is meant to exclude the production of foamed plastics as a material or where raw product is processed. In that case the building may fall into risk group WS or required another compliance approach such as C/VM2. The definition of foamed plastics is quite broad in terms of the composition of the material and does not give any consideration to any other treatments or fire retarding properties.
What about a factory used to construct prefabricated buildings where SIP panel with EPS core (fire retarding type) is used as a component in the production? I am dealing with this scenario at the moment where the building otherwise fits neatly within risk group WB.
I would appreciate hearing from anyone that has any experience or thoughts on this issue.
WS Risk Group corresponds with the Building Use WF which caters for buildings with medium or high fire loads that could have ultra fast fire growth. Risk Group WS implies that because you have over certain heights (5.0 m and 8.0 m) you can expect ultra fast fire growth. C/AS2 is a blunt instrument.
So I believe the issue here is; can you expect ultrafast fire growth? If you can - then I would use Risk Group WS.
So the question now becomes - will you get ultrafast fire growth from fire retardant treated EPS.
There should be data on this somewhere - hunt it down. My understanding of fire retardant treated product is that the fire retardant treatment just makes it harder to initiate a fire in the target. Once the fire starts, the fire behaviour of the treated combustible is only marginally different from the untreated combustible. So unless you have data to prove otherwise I would treat your fire retardant treated EPS as also having an ultrafast fire growth rate (albeit harder to ignite) and apply the WS Risk Group.
Fire retardant EPS foam cores are not as easy to ignite as normal EPS cores, but burn just as well. NZBC C/AS2 actually does not include foam plastics manufacturing in WB or WS, therefore I suggest should use either C/VM2 or an alternative solution. Please ensure that the EPS complies with AS 1366. This is particularly important for SIPs panels with PU foam in place.