Fire resistance levels are specified in the Building Code of Australia. This system supersedes the old fire ratings and provides an accurate method of predicting the ability of a wall to maintain strength in a fire and to resist its spread. The fire resistance level (FRL) specifies the fire resistance periods (FRP) for structural adequacy, integrity and insulation. These components are described below.
The ability of a wall to continue to perform its structural function.
The ability of a wall to maintain its continuity and prevent the passage of flames and hot gases through cracks in the wall.
The ability of a wall to provide sufficient insulation such that the side of the wall away from the fire does not exceed a predefined rise in temperature.
Fire Resistance Level
The fire resistance level is expressed in minutes for each of these periods and always in the same order. For example an FRL of 90/90/90 means a fire resistance period of 90 minutes each for structural adequacy, integrity and insulation.
Factors Influencing Fire Resistance Level
The fire resistance level of a wall depends not only on the thickness of the wall but also on its height, length and boundary conditions (i.e. how it is connected to other building elements). For this reason it is impossible to give an FRL for a particular brick as the fire resistance period for structural adequacy is specific to the wall type and its boundary support conditions.
The CBPI publication, Design Manual 5, Fire Resistance Levels for Clay Brick Walls (revised and republished March 1999 , fully explains the system and allows designers to assess the fire resistance level for a specific wall type. A series of charts enables the designer to directly read the FRP for structural adequacy for a given wall.