Fire Resistance
Fire Terms and Definitions
Fire Resistance Level
Fire systems are rated to withstand a fire under test conditions for a certain period of time. This time is known as the Fire Resistance Level (FRL) and consists of the three criteria listed below:
The example above shows an FRL of 60/60/60. This means that during a fire test, the system did not fail for 60 minutes for each of the criteria.
A dash in an FRL means that there is no requirement for that criterion. For example, 90/–/– means there is no requirement for Integrity and Insulation. Structures such as non-load bearing walls do not have an FRL requirement for Structural Adequacy, for example –/60/60.
Resistance to Incipient Spread of Fire (RISF)
Resistance to the Incipient Spread of Fire (RISF) is the ability of a ceiling to limit the temperature rise in the ceiling cavity [shown below]. The RISF is a requirement of the BCA in specific applications. It is aimed at preventing ‘flashover’, which is when a fire starts spontaneously due to high temperatures. The RISF for Lafarge fire rated ceilings are stated in the system tables.
Acceptable Variations to Fire Rated Systems
Fire rated systems must be built according to the installation instructions in Section 4. However, there are some variations allowed that will not degrade the performance of the system:
- Increasing cavity width
- Increasing stud size or metal thickness
- Adding noggings to support fixtures or services
- Decreasing stud spacing
- Decreasing fastener spacing
- Substituting 13mm FireShield with 13mm MultiShield or 13mm ImpactShield
- Substituting 16mm FireShield with 16mm MultiShield
- Adding non-combustible layers to a system up to a weight of 20 kg/m2 and no thicker than 25mm. This includes fibre cement board up to 9mm thick and plasterboard up to 25mm thick. For load bearing walls, the load per stud must include the extra lining.
Modifications to Fire Rated Systems
Fire rated systems are often modified by the installation of:
- Fire rated inspection hatches
- Fire rated power points
- Fire rated light fittings
- Fire rated doors
- Fire dampers
- Electrical cables
- Metal or plastic pipes
- Other fire rated penetrations
It is the responsibility of the manufacturer of these components to ensure that the fire and acoustic properties of the plasterboard system are maintained.
[Some modifications are detailed in section 4]. Any modification not covered in this manual must be according to the relevant manufacturer’s instructions.
Smoke Walls
The purpose of a smoke wall is to prevent smoke passing from one side of a wall to the other. The perimeter and all penetrations must be sealed with fire sealant. A smoke wall must be built from non-combustible materials such as plasterboard, compounds, glasswool insulation and fire sealant.
Doors and windows used in smoke walls must comply with requirements in the BCA Specification C2.5. Ducts through the smoke wall must use a smoke damper, unless the duct is part of the smoke handling system and is required to function during a fire.
Class 9a health care buildings
Smoke walls in Class 9a buildings must extend up to:
- A non-combustible roof or
- A ceiling having a RISF of 60 minutes.
Class 9c aged care buildings
Plasterboard used for smoke walls in Class 9c buildings must have a thickness of at least 13mm. Smoke walls in
Class 9c buildings must extend up to:
- A non-combustible roof or
- A jointed plasterboard ceiling with a minimum thickness of 13mm.
