Changes to assessing interior surface linings

This Issue This is a part of the Fire feature

By - , Build 132

Changes to Building Code clauses C1–C6 Protection from fire have meant significant changes to the fire safety specifications for interior surface linings.

Figure 3: The ISO 5660, or cone calorimeter, test.
Figure 1: Full-scale ISO 9705 test.
Figure 2: Heat release rates in ISO 9705 test determines the group number.
Figure 1: Full-scale ISO 9705 test.

THE SPECIFICATION for interior surface linings for fire safety has changed significantly with the introduction of:

  • quantitative performance requirements specified in the Building Code – previously the Code had qualitative statements, with the specific spread of flame (SFI) and smoke developed (SDI) indices in the Acceptable Solutions
  • a completely new method of assessing the fire hazard of wall and ceiling lining requirements based on a group number classification, replacing the SFI/SDI.

Risk groups and group numbers

The new Acceptable Solutions are published as stand-alone documents – one for each risk group. Risk groups are used to group together occupancies – or purpose groups – with a similar fire risk.

Each Acceptable Solution has the same format and section numbering to aid navigation but only contains requirements relevant to the particular risk group. The group requirements are in Table 4.1 of each document.

The group number system relates to the propensity for a material on a wall or ceiling to spread flame across the surface and contribute additional heat to the fire. The scale ranges from group 1 (best) to group 4 (worst). A group 1 surface lining would contribute little to fire spread, while a group 4 surface lining would exhibit extremely rapid fire spread resulting in early flashover and full room involvement.

Maximum permitted group numbers for specific locations within a building reflect the level of safety required in those locations. For example, a designated fire exit route must have the safest linings (group 1 material), while there is less restriction on surface linings in generally occupied areas.

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New Verification Method

Fire safety requirements for most conventionally designed buildings can be specified using the Acceptable Solutions.

For more complex buildings where innovative solutions are proposed, engineering analysis is required using a new Verification Method (C/VM2). While performance criteria in the form of group numbers are specified in the Building Code and in simpler terms in the individual Acceptable Solutions, the actual means of calculating a group number is contained in an appendix to C/VM2.

Figure 2: Heat release rates in ISO 9705 test determines the group number.

Both the base material and any treatments or surface-applied coatings affect the fire properties of surface linings. To determine a group number, the complete surface lining system is evaluated using one of two alternative test methods – ISO 9705, the full-scale reference scenario fire test, or ISO 5660, a less expensive bench-scale fire test.

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Full-scale ISO 9705 test

In the ISO 9705 test, a small bedroom-sized room is lined with the test material on the walls and ceiling. A gas burner – representing a burning waste paper basket – is placed in a corner very close to the wall surfaces (see Figure 1).

In the 20 minute test, the gas burner provides 100 kW output for 10 minutes and then 300 kW for the second 10 minutes. The burner flame may ignite the linings. The time at which the room reaches flashover or full room involvement – defined as exceeding 1000 kW for this test scenario – determines the group number (see Figure 2). The best performing to the worst is:

  • group 1 = no flashover during test
  • group 2 = flashover between 10 and 20 minutes
  • group 3 = flashover between 2 and 10 minutes
  • group 4 = flashover before 2 minutes.

A group 4 material is deemed too hazardous to building occupants, and the Building Code doesn't permit its use in any location where surfaces finishes are regulated.

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Bench-scale ISO 5660 test

The alternative ISO 5660 test method – referred to as the cone calorimeter test because of the cone-shaped heating coil – works on the same principles as the full-scale ISO 9705 test.

In this test, 100 mm square specimens are placed under a heating coil and subjected to an imposed heat flux of 50 kW/m² (see Figure 3). The resulting heat release rate data is used to predict the time to flashover in the ISO 9705 test, and a group number is assigned.

The ISO 5660 test is suitable for most lining materials and offers a cheaper and quicker alternative to the ISO 9705 test. Because the test specimens are relatively small, the prediction method typically results in a group number that is the same or higher – more conservative – than the likely result from full-scale testing to ISO 9705.

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Smoke measured as well

Smoke production levels are measured in both the full-scale room and cone calorimeter tests. If these are within the Code – defined limits for group 1 or 2 materials, it is denoted with an S postscript, for example, group number 1S.

Smoke production is only regulated in locations without sprinklers, where group numbers 1 or 2 are required, and is not needed for other locations requiring group number 3, where the risk and smoke hazard is dominated by the burning contents rather than the surface linings.

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Transition to new approach

This new approach to managing fire spread on interior surface linings reflects international trends towards using test methods that more closely represent real fire scenarios. These changes also more closely align the test requirements of the Australian and New Zealand Building Codes.

The new requirements were introduced in April 2012 with a 12-month transition period during which the fire properties of surface linings may be specified using either SFI/SDI or group numbers. After April 2013, only group numbers will apply.

Figure 3: The ISO 5660, or cone calorimeter, test.

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For more

Contact BRANZ Fire TestingTeam Leader Peter Whiting, email [email protected] or phone (04) 238 1331.

Download the PDF

Articles are correct at the time of publication but may have since become outdated.

Figure 3: The ISO 5660, or cone calorimeter, test.
Figure 1: Full-scale ISO 9705 test.
Figure 2: Heat release rates in ISO 9705 test determines the group number.

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