Current affairs In any instances where smoke control
systems interact with other systems in a fire situation, it is important to ensure that this interaction should not compromise the operation and effectiveness of the smoke control system. Overall performance criteria and system design will vary, depending on the layout of the common corridor or lobby within the apartment building. Where travel distances are no more than
7.5m from the door to the staircase along to the more remote apartment entrance door, the principle objective will be to ensure that the stairway(s) remain predominantly free of smoke. However, where corridors are extended, both the staircase and the common corridor will require protection.
Methods of smoke control
Three common methods are used to limit the spread of smoke in the common areas of apartment buildings. These are:
1. Natural smoke control systems. 2. Mechanical smoke ventilation systems. 3. Pressure differential systems.
Small single stair buildings require their own system type, since the functional requirements
for the systems – whether natural, pressurisation or powered – are slightly different from other residential building types.
Natural ventilation This method of ventilation has many benefits, including simplicity, reliability, low noise and low energy use. However, the performance of it can be sensitive to wind effects and, for natural shaft systems, there is a relatively large loss of floor space. Natural ventilation works by harnessing the natural forces of wind and thermal buoyancy to drive flow through the ventilator. In this application, the intended driving
force is the buoyancy of hot smoke from the fire. Since buoyancy forces can be small compared to wind forces, the performance in use can be significantly affected by wind. For natural ventilation to operate effectively, there needs to be both a source of inlet air and an exhaust opening. In the case of a wall mounted vent, the
vent generally provides both inlet at the bottom of the vent and exhaust at the top. Otherwise, inlet air can be provided through the stair door when it is opened. To assist this, and to vent any smoke which enters the stair, a vent is needed at the head of the stair.
FOCUS
www.frmjournal.com SEPTEMBER 2018
41
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