Fire properties of building products are regulated to minimize rapid fire spread and smoke growth in buildings and ensure 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.
What is a group number?
Group numbers can be obtained from either of the following test methods:
- A full-scale corner room burn test in accordance with AS ISO 9705-2003 test or,
- 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 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 the assessment of 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 a further 10 minutes.
- Group 2 – Material that reaches flashover following exposure to 300 kW within 10 minutes after not reaching flashover having first been 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.
Group numbers obtained via 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 for the purposes of determining group numbers, the material being tested 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 intended use of a material is 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 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 in the duct. The group number is determined by measuring the ‘time to flashover’.
Group numbers obtained via 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 to be tested using cone calorimetry tests.
Only materials that have confirmed correlations between the results obtained from cone calorimetry and those obtained from the corner room burn test (this means the materials must be subjected to corner room burn test conditions as well as cone calorimetry) can be tested using the cone calorimeter for the purpose of determining a group number. Examples of such materials are:
- painted or unpainted paper-faced gypsum plasterboard
- un-treated solid timber and wood products such as particleboard, plywood and medium-density fibreboard (MDF)
- rigid non-thermoplastic foams such as polyurethane.
Group numbers for multi-layered specimens can be determined by cone calorimetry, 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 of the substrates 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.
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 of 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.
Systems in which fixings and joints play a critical part in the fire hazard properties of a product are not suitable for testing in the cone calorimeter for the purpose of determining group numbers, despite having demonstrated correlations with the room burn tests.
For more information, go to www.warringtonfire.com
- Standards Australia, Determination of fire hazard properties Wall and ceiling linings, 2015
- Standards Australia, Method of test for heat and smoke release rates for materials and products using an oxygen consumption calorimeter, 1998 (R2016)
- International Organization for Standardization 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)
- Standards Australia, Fire tests – Full-scale room test for surface products, 2003 (R216)
- Paint or fire-retardant coatings must not be used to achieve compliance with the required group number.