The principle of natural smoke extraction: Adexsi

The Principle of Natural Smoke Ventilation

Natural smoke ventilation is crucial to managing fire safety in buildings. By using the physical properties of hot smoke, which rises due to its low density, natural smoke extraction keeps areas close to the ground safer, with lower temperatures, less toxic air and higher oxygen concentrations.

HOW NATURAL SMOKE VENTILATION WORKS

Natural smoke extraction is based on thermal draught, using external air inlets and smoke outlets in the roof, known as smoke extraction vents or SHEVs. These smoke extraction vents communicate directly with the outside, enabling smoke to be effectively evacuated.

COMPARTMENTALISATION FOR EFFECTIVE SMOKE EXTRACTION

To prevent smoke from spreading, it is essential to compartmentalise the areas to be cleared of smoke. This compartmentalisation is achieved by means of vertical screens or smoke barriers located at the top of the premises, under the roof or ceiling. These screens delimit cantons whose surface area must not exceed 1600 m² and whose largest dimension must not exceed 60 m.

KEY PARAMETERS FOR NATURAL SMOKE VENTILATION

The effectiveness of natural smoke extraction depends on a number of factors:

Effective opening area of smoke vents: This must be adapted to the surface area of the fire, the type of operation, the height of the room and the thickness of the smoke layer.
Positioning air inlets: Positioning air inlets at the bottom of the building is crucial to optimise smoke extraction.

OBJECTIVES OF NATURAL SMOKE VENTILATION

Natural smoke ventilation aims to :

Keep escape routes passable for occupants and facilitate evacuation of the building in the event of fire.
Make it easier for emergency services to intervene by reducing toxic gases, maintaining a sufficient level of oxygen and maintaining maximum visibility.

THE DANGERS OF SMOKE

The smoke and combustion gases produced during a fire present a number of dangers to the safety of people and property:

Temperature : Hot smoke can cause internal burns and facilitate the spread of fire by pyrolysing combustible materials.
Opacity: Smoke reduces visibility, complicating evacuation and delaying rescue operations.
Asphyxiation : The fire consumes oxygen, leading to a risk of asphyxiation for the occupants.
Toxicity : The gases emitted, such as carbon monoxide (CO), nitrogen oxides (NOx) and hydrocyanic acid (HCN), are extremely dangerous.
Corrosivity: Some acidic unburnt gases can damage building structures and equipment.

Conclusion

Natural smoke ventilation is essential for fire safety. By taking advantage of thermal draught, it enables smoke to be evacuated efficiently, reducing the risk to occupants and facilitating emergency response. Adequate compartmentalisation and installation that complies with standards are essential to ensure that natural smoke ventilation is effective.

Smoke ventilation