Smoke Ventilation

With the new editions of Uniform Fire and Life Safety Codes throughout the AGCC the difference between smoke ventilation and natural ventilation needs to be clarified. In the Code, only relatively small compartments can have natural ventilation as the smoke ventilation method. Above these sizes the smoke ventilation requires electrical driven force draft fans that are approved by Civil Defense. Larger compartment sizes require fully engineered smoke ventilation systems.

Smoke purging for single storey industrial buildings usually involves a roof mounted extract fan that is rated for high temperature operations and often the manufacturers offer a dual speed fan and claim they can used for general ventilation purposes. Other systems for multi storey buildings are much more complex and involve ducting and special fan controls.

The requirements for smoke ventilation are determined by the various codes and are calculated using mathematical algorithms that are based on the different types of incidents that could occur. Primarily smoke ventilation is designed to remove as much smoke and heat that is possible during a fire incident. Other factors may impinge on this requirement such as sprinklers and local codes.

Whatever the requirements, as these are for life and fire safety, the fans must be fully operational at all times and be maintained to operate at their designed capacity. Often the fans are supplied through a dedicated poser supply since in a typical industrial building the normal poser supply will be cut automatically through the circuit breaker to prevent electrocution of the fire firefighters.

General Ventilation

All industrial buildings in this region (the Arabian Gulf) require ventilation for their day to day operations. In this environment, the extract system must be capable of withstanding high temperatures, humidity, very fine abrasive dust, pollutants such as oil mists and from time to time VOC’s and mildly corrosive atmospheres. Experience has clearly demonstrated that unless specialized fans fitted with HEPA filters are used, electrically driven forced draft fans are expensive to use and require considerable maintenance to perform to their full capacity.

Ventilation rates for general purpose ventilation are often determined by experience as the flow is subject to the law of diminishing returns. In other words there is a limit the amount of internal comfort that can be achieved and that is determined by the temperature of the outside air that is being supplied to provide the ventilation.

The preferably ventilation system for this type of application is natural ventilation using roof mount ventilators. There are many types of these ventilators that include ridge, rotating (wind driven) and now cylindrical static (Hurricane® Plus). The advantages of using this system is its low running and maintenance costs.

Can Dual Speed fans be used for General Ventilation?

Probably not. Despite the recommendations from the suppliers of these fans, smoke ventilation extract fans are a dedicated life and fire safety apparatus. Use of these fans for general purpose ventilation is costly in both electrical consumption and maintenance particularly as the maintenance must be carried out by approved fire and life safety maintenances companies.

Failure of these fans due to incorrect use in a fire incident could jeopardize life and any insurance cover.

Sustainable Energy Codes

Obviously the use of any electrically driven forced draft fan when natural ventilation can be used effectively is not in accordance with any sustainable energy policy or codes. Community Social Responsibility (CSR) requires the use of sustainable energy devices whenever possible.