Fire Hazard Properties of Internal Wall and Ceiling Linings

The fire properties of building products are regulated to minimize rapid fire spread and smoke growth in buildings and ensure the safe and timely evacuation of occupants. This guide describes the compliance pathways available under the Deemed-to-Satisfy provisions for fire hazard properties of internal wall and ceiling linings, in accordance with Specification C1.10 of the National Construction Code (NCC) 2019, Volume One.

Group Numbers and Fire Performance

The group number is a value from 1 to 4, which indicates how readily a material ignites and releases heat. Group 1 materials are the least combustible, while Group 4 materials are the most combustible. To comply with NCC 2019, Specification C1.10, Clause 4(a), wall and ceiling lining systems must meet the requirements of the group number assigned for that particular building classification and location. For example, walls in public corridors of class 2 or 3 sprinklered buildings are assigned Group numbers 1,2 and 3.

Per Specification C1.10, the group number must be determined in accordance with AS 5637.1 and can be obtained from either of the following test methods:

1. A full-scale corner room burn test in accordance with AS ISO 9705-2003 test or,
2. When appropriate, prediction using data from a small-scale cone calorimetry test in accordance with AS/NZS 3837:1998 (R2016) or ISO 5660-1.

The group number is essentially a numeric representation of the performance achieved during the AS ISO 9705-2003 (R2016) corner room burn test and is used as a benchmark for assessing internal surface linings when exposed to fire. It can be determined by measuring ‘time to flashover’ when tested in accordance with AS ISO 9705-2003. The time to flashover is defined as the time taken for the total heat release rate (HRR) to reach 1 MW.

The group number of a material is assigned as follows when tested in accordance with AS ISO 9705-2003:

• Group 1 – Material that does not reach flashover when exposed to 100 kW for 10 minutes, followed by exposure to 300 kW for another 10 minutes.
• Group 2 – Material that reaches flashover following exposure to 300 kW within 10 minutes after not reaching flashover after being exposed to 100 kW for 10 minutes.
• Group 3 – Material that reaches flashover between 2-10 minutes when exposed to 100 kW.
• Group 4 – Material that reaches flashover within 2 minutes when exposed to 100 kW.

Obtaining Group Numbers Through Corner Room Burn Tests

An AS ISO 9705 corner room burn test is a common reaction-to-fire test used to investigate the potential fire spread, smoke density and the heat release rate of a surface lining product when exposed to fire. The room (sized 3.6m × 2.4m × 2.4m) consists of four walls at right angles, a doorway and a ceiling.

When testing to determine group numbers, the material must be affixed to three walls and the ceiling, leaving the wall with the doorway opening unlined. The fixing methods used to mount the specimen shall, as far as possible, be the same as those used in practice. Even if the material is intended to be used as a ceiling or wall lining only, tests for walls or ceilings alone cannot be used to determine group numbers.

The test procedure involves a burner in the corner of a room that subjects the test specimen to an exposure of 100 kW for 10 minutes, followed by 300 kW for 10 minutes. The exhaust gases are collected by the extraction hood and analysed to determine the concentrations of oxygen, carbon dioxide (CO2), carbon monoxide (CO) and the optical smoke density. The HRR is calculated by oxygen consumption calorimetry, while the smoke production rate (SPR) is determined from the optical smoke density and flow rate within the duct. The group number is determined by measuring the ‘time to flashover’.

Obtaining Group Numbers Through Cone Calorimetry

Cone calorimetry tests in accordance with AS/NZS 3837 or ISO 5660-1 involve exposing a 100mm-by-100mm flat specimen to a 50 kW/m2 incident heat flux generated by a cone-shaped heating element. Tests are performed in the horizontal orientation. The data recorded is the same as the AS ISO 9705 corner room burn test, plus the mass loss. Like the corner room burn test, the HRR is determined from oxygen consumption calorimetry.

The group number is determined from an empirical model, which predicts the likely range of flashover times if the same material was tested under full-scale corner room burn conditions in accordance with AS ISO 9705–2003. Not all materials are suitable for cone calorimetry testing.

Suitable Materials for Cone Calorimetry. For the purpose of determining a group number, only materials that have confirmed correlations between the results obtained from cone calorimetry and those obtained from the corner room burn test can be tested using the cone calorimeter. Examples include:

• Painted or unpainted paper-faced gypsum plasterboard.
• Untreated solid timber and wood products, such as particleboard, plywood and medium-density fiberboard (MDF).
• Rigid non-thermoplastic foams such as polyurethane.

Cone calorimetry can determine group numbers for multi-layered specimens, provided there is a demonstrated correlation between the cone calorimeter and room burn test for each individual layer. Each layer, including adhesive layers on the upper face of each substrate, needs to be tested. The group number assigned to the system is based on the layer or combination of layers that achieved the highest group number.

Materials Unsuitable for Cone Calorimetry. Cone calorimetry tests are not suitable for:

• Profiled surfaces where more than 50% of the surface is rebated more than 10mm from the highest point.
• Materials containing joints, large holes, cracks or fissures.
• Materials that melt or shrink away from a flame.
• Materials that intumesce, swell, bend or collapse appreciably when exposed to radiant heat.
• Materials with a reflective surface.
• Linings in which surface coatings or layers are capable of delaminating from the substrate.

For the purpose of determining a group number, systems in which fixings and joints play a critical part in a product’s fire hazard properties are not suitable for testing in the cone calorimeter despite having demonstrated correlations with the room burn tests.

References

1. Standards Australia. (2003). Fire tests – Full-scale room test for surface products (AS ISO 9705-2003).
2. Standards Australia. (1998). Method of test for heat and smoke release rates for materials and products using an oxygen consumption calorimeter (AS/NZS 3837:1998).
3. International Organization for Standardization. (2015). Reaction-to-fire tests — Heat release, smoke production and mass loss rate — Part 1: Heat release rate (cone calorimeter method) and smoke production rate (dynamic measurement) (ISO 5660-1:2015).
4. Standards Australia. (2015). Determination of fire hazard properties wall and ceiling linings (AS 5637.1:2015).