Staircase ventilation – Smoke spread patterns in a staircase equipped with different smoke extraction systems

Staircase fire protection systems are designed to save human life by exhausting smoke in the event of a fire. This is a popular solution as it is relatively cost-effective compared to more complex pressure differential systems. It is worth to know how these systems operate in real fires.

Staircase fire protection systems – smoke spread patterns during a fire

The research conducted as part of the project allowed to discover how smoke flows into and spreads inside staircases. The video below shows a comparison of two smoke exhaust systems: on the left you can observe how smoke affects the staircase using the simplest gravity smoke ventilation system, and on the right you can see the operation of the smoke exhaust system supported by mechanical ventilation. It is clear that opening the door to the staircase equipped with a gravity system causes smoke to fill the entire space of the staircase at the height of the storey covered by fire, which significantly reduces visibility. This is the initial stage of fire development. At this point the smoke temperature is still relatively low.

Smoke spreading during a fire

From the very beginning, the mechanical airflow system directs the smoke towards the smoke damper. The smoke does not fall on the escape route below the storey engulfed in fire, which facilitates the evacuation process and the arrival of the fire brigade teams. As the fire gets bigger and the temperature of the smoke flowing into the stairwell rises, visibility on the test floor with the gravity system begins to improve.

Research on staircase fire protection systems

The research shows that in order to make a gravitational smoke exhaust system effective it requires an external force to compel the smoke flow in the staircase. This force may be the high temperature of the fire gases or the favourable temperature of ambient air. Without it the smoke will remain in the staircase. The force can also be a properly selected mechanical air supply. Such a solution is presented on the right side of the video.

It is worth noting that the research was carried out for a well-oxygenated fire. In the case of oxygen-depleted fires, the temperature of the smoke may be too low. In such a case smoke will not reach adequate buoyancy and will remain in the staircase when using a gravity system. The gravitational smoke exhaust system will not work effectively under such conditions. The use of mechanical air supply with appropriate efficiency allows for effective smoke extraction from the staircase, regardless of external factors.

Izabela Tekielak-Skałka

Head of the CFD Research and Analysis Department

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