2 Determine the passive fire control protection / Fire Resistance Level ( FRL ) of the external and internal fire separating walls. You will need to identify: Elements affected by Fire Source Feature (FSF) - specific walls, roofs or floors affected Fire Resistance Level (FRL) of each building element facing an FSF Materials or system used to achieve FRL How the construction project will achieve the required FRL For example, how will the external and internal fire separating walls be constructed