A separate extract system should be provided to remove the extinguishant after discharge. The system will need to have motorised fire dampers that are closed in normal operation and during extinguishant discharge.
In some cases it may be acceptable to ventilate the protected area after discharge through externally opening doors and windows, but it will be necessary to talk to the authority having jurisdiction through the building control officer or fire officer and the insurer if the designer or specialist is planning to install anything other than a dedicated mechanical extract system.
The ventilation system may be under the control of the local fire authority who will operate it when sure that the source of activation of the extinguishing agent has been dealt with successfully.
Where possible the extract to pass straight to outside about passing through any other space, discharging directly to the atmosphere with out any possibility of recirculation. A damp out with a positive shut off must be fitted to prevent excessive leakage of extinguishing agent in the event of a discharge. Such a system can, however, be used in some systems to provide a pressure relief at the time of discharge. If so, a pressure relief/flap must be installed.
