The what and how of fire hazard properties for wall and ceiling linings

For wall and ceiling linings, the NCC doesn’t just require what the fire hazard properties must be, but also stipulates how they are to be determined.

Performance Requirement CP4 achieves tenable evacuation conditions by requiring materials and assemblies in Class 2 to 9 buildings to appropriately resist spread of fire and limit the generation of smoke, heat and toxic gases. Deemed-to-Satisfy (DTS) Provision C1.10(a)(ii) achieves this in part by requiring wall and ceiling linings to meet the fire hazard properties of Specification C1.10. Clause 4(a) of that Specification requires—

a) for non-sprinkler protected buildings: a smoke growth rate index not more than 100 or an average specific extinction area less than 250 m²/kg; and

b) for all buildings: a group number, the specific value of which varies with building classification, location, and if the building is sprinkler protected.

For each of the above, FPAA101D and FPAA101H sprinkler systems do not constitute sprinkler protection.

The smoke growth rate index and average specific extinction area are values derived by test that reflect the extent to which smoke produced by a burning material reduces visibility. Group number is a value from 1 to 4, derived by test, which represents how readily a material ignites and releases heat. Group 1 materials are those that perform best in a fire, and group 4 materials are those that perform worst.

There are two test methods for determining the group number of a wall or ceiling lining.

The first is described in the Standard AS ISO 9705-2003 Fire tests—Full-scale room test for surface products. Under this method, a room of standard dimension is constructed from the lining submitted for test. A heat flux meter is installed and the room is ignited at one corner. Data obtained from this test includes the time at which (if at all) the heat flux meter records 1 MW (i.e. when flashover occurs), relative to the heat applied at the ignition source.

The second test method is an oxygen calorimeter test, often referred to as the ‘cone calorimeter test’ on account of a cone-shaped heater in the test apparatus. For the purposes of the NCC, the test may be performed in accordance with AS/NZS 3837:1998 Method of test for heat and smoke release rates for materials and products using an oxygen consumption calorimeter or ISO 5660-1 Heat release rate (cone calorimeter method) and smoke production rate (dynamic method). This is a small-scale test where a lining specimen is installed in a test apparatus capable of measuring fire performance data, including oxygen consumption, heat flux and smoke obscuration. For some materials, this data can be used to predict how the lining would perform in a full-scale test and a group number can be allocated accordingly.

Both tests measure smoke obscuration, and the first test method is significantly more expensive to perform than the second.

No. Clause 4(b) of Specification C1.10 requires the fire hazard properties for wall and ceiling linings to be determined in accordance with AS 5637.1:2015 Determination of fire hazard properties—Wall and ceiling linings (AS 5637.1). Prediction of group number using results obtained from an oxygen calorimeter test is only suitable for certain materials, therefore AS 5637.1 limits use of that test method accordingly.

Generally, group number prediction based on an oxygen calorimeter test is only suitable for gypsum plasterboard, solid timber, wood products such as particleboard and plywood, and rigid non-thermoplastic foams such as polyurethane. The oxygen calorimeter test  cannot be used for linings with joints, openings, profiled facings or reflective surfaces, or for linings that contain materials that melt or shrink away from a flame.

Further detail is found within the Australian Standard AS 5637.1.

Because the NCC stipulates how the group number is to be determined, besides what it is to be, it is important to ensure both the what and the how are complied with.