FRL is the technical description of the level of fire protection of a particular structure, sometimes referred to as the ‘fire rating'. An FRL gives a specific measure for an item, and it should always be quoted rather than using a simple generalization.

The FRL of member or structure is summarized as a series of three numbers representing the nominal grading period in minutes, assessed by subjecting a sample to a fire test according to AS 1530.4. These numbers indicate, from left to right, the item's structural adequacy, integrity, and insulation rating:

1. Structural Adequacy is a measure of the length of time before the test item fails under load.

2. Integrity is a measure of the temperature at which cracks or openings appear in the test item that permit the escape of hot flames or gases.

3. Insulation is the measure of the time taken for the temperature on the side of the test item not exposed to fire to rise above the stated specified under AS1530.4.

An example of this would be a typical ‘ 2 hour fired duct' which will have an actual FRL of / / .