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- Class A System:
For means of escape. Defend in place
The design conditions are based on the assumption that a building will not be evacuated unless directly threatened by fire. The level of fire compartmentation is such that it is usually safe for occupants to remain within the building. Therefore, it is unlikely that more than one door onto the protected space (either that between the stair and the lobby/corridor, or the final exit door) will be open simultaneously. Class A system shall not be used in mixed use developments.
- Class B System:
For means of escape and firefighting
A Class B pressure differential system can be used to minimize the potential for serious contamination of firefighting shafts by smoke during means of escape and fire service operations.
During firefighting operations it will be necessary to open the door between the firefighting lobby and the accommodation to deal with a potentially fully developed fire.
- Class C System:
For means of escape by simultaneous evacuation
The design conditions for Class C systems are based on the assumption that the occupants of the building will. all be evacuated on the activation of the fire alarm signal that is simultaneous evacuation. In the event of a simultaneous evacuation it is assumed that the stairways will be occupied for the nominal period of the evacuation, and thereafter will be clear of evacuees. Consequently, the evacuation will occur during the early stages of fire development, and some smoke leakage onto the stairway can be tolerated. The. airflow due to the pressurization system shall clear the stairway of this smoke. The occupants being evacuated are assumed to be alert and aware, and familiar with their surroundings, thus minimizing the time they remain in the building.
- Class D System:
For means of escape. Sleeping risk
Class D systems are designed in buildings where the occupants may be sleeping, e.g. hotels, hostels and institutional-type buildings. The time for the occupants to move into a protected area prior to reaching the final exit can be greater than that expected in an alert or able-bodied environment, and occupants may be unfamiliar with the building or need assistance to reach the final exit/protected space. Class D systems are also appropriate when the presence of a pressure differential system has served to justify the absence of a discounted stairway and/or lobbies that would normally be required under the national provisions valid in the place of use of the system.
- Class E System:
For means of escape by phased evacuation
A Class E system is a system used in buildings where the means of escape in case of fire is by phased evacuation. In the “phased evacuation” scenario it is considered that the building will still be occupied for a considerable time whilst the fire is developing, creating greater fire pressures in addition to greater amounts of hot smoke and gas (this can vary greatly according to the type of materials, fire load involved and the geometry of the fire load). In the “phased evacuation” situation, the protected staircases shall be maintained free of smoke to allow persons to escape in safety from floors, other than the fire floor, at a later stage in the fire development.
- Class F System:
Firefighting system and means of escape
A Class F pressure differential system can be used to minimize the potential for serious contamination of firefighting staircases by smoke during means of escape and fire service operations. During firefighting operations it will be necessary to open the door between the firefighting lobby and the accommodation to deal with a potentially fully developed fire.
