Natural smoke and heat exhausting

Why devices for the smoke and heat exhausting?

The destructive action of fire requires the designing and construction of such living and production buildings, which prevent, in the case of fire, its spreading over the room, and assure safe evacuation of people and of material goods, as well as the efficient extinction of the risen fire.

It is known that the inside repartition of premises into the fire sections, mutually separated with the fire walls, prevents spreading of fire. Nevertheless, the up-to-date production and storage technology requires, nowadays, large and non-partitioned premises.

The extinguishing of the fire in large premises is difficult and dangerous in spite of the most recent fire-fighting equipment. Smoke and heat spread rapidly in the burning room, so, that even a small fire may create a thick, hot smoke atmosphere within a short time, impeding breathing and diminishing visibility. For that reason the rescuing of people and of material goods from the premises in fire, as well as the intervention of the firemen, is very difficult, and in some cases practically impossible.

The fire spreads owing to the heat radiation, as well as owing to the transfer of fire on the burning objects on the floor and the burning ceiling structures, respectively ceiling claddings. On the spots where a large quantity of material is on fire, the non-burnt gases may accumulate under the ceiling. If the gases are mixed with the air (in case of the broken wall window, or similar), an explosion or a lightning combustion occur, and consequently, a rapid spreading of fire.

This can be prevented by the outlet of the hot flue gas and heat through the roof opening into the open air. In this way the air close to the floor does not contain such a large quantity of smoke and heat.

The skylights (sky domes and light bands) can thus be used in normal conditions for the lighting and air ventilation of rooms, while in the case of fire they can serve as a natural smoke and heat exhausting from the burning premises.

If the devices for the natural smoke and heat exhausting are correctly dimensioned and positioned, and, if in the case of fire they open in due time, we achieve that the layer of smoke and hot gases does not spread across the defined limit, and in this way the devices enable and facilitate:

• protection of the exit ways against enclouding,
• quick intervention of firemen,
• protection of the building structure, equipment, installations, and other material goods, against fire.

The preliminary condition for the efficient operation of devices for the natural exhausting of smoke and heat is that, in the case of fire, the air inlet openings, that is, the wall windows are opened quickly, if possible.

It is important, too, that the fire-fighting system includes a fire-detection system with the automatic fire alarm as well, as only thus the intervention of the firemen can be quick and successful.

Sketch: Building without smoke and heat exhausting	Sketch: Building with smoke and heat exausting

Types of devices for the natural smoke and heat exhausting

• pneumatic ( CO₂) actuators,
• mechanic ( PMC) actuators,
• electromotive actuators (activating through the fire central, respectively, fire detection device).

The activation of devices for the natural smoke and heat outlet is carried out:

• through the thermo bulb, which is activated at a certain temperature,
• through the fire central, respectively, fire detectors.

The devices for the natural smoke and heat exhausting are usually activated at the temperature between 68 and 141 °C, regardless the requirements of a certain project.

CO₂ actuators
These are the actuators of the pneumatic design. The opening is based on the principle that in the case of fire at a certain temperature the thermo bulb activates, which then activates the CO₂ bottle and the propellant fills the pneumatic cylinder - and the piston rod opens the skylight.

Considering the requirements of a particular project, the activation of the CO₂ can be done with the thermo bulb or with the signal of the fire central, respectively, fire detectors, as for instance manual detectors, smoke sensors, and similar devices.

• They are used at various opening angles and are suitable for more significant loadings of skylights.
• The advantage of the CO₂ opening mechanisms is easier closing of skylights after their opening (possibility of closing from the floor). The CO₂ bottles are suitable for single use only; therefore they have to be obligatorily replaced after the activation.
• The CO₂ actuators are used only for the systems of the natural smoke and heat outlet (not for the air ventilation); in the case when the air ventilation is required, too, the actuators can be combined with the electromotive opening.

Mechanical (PMC) actuators
These are the actuators of the mechanical design. The opening is based on the principle that at a certain temperature the thermo bulb activates the pre-stressed spring in the cylinder, which, when released, opens a skylight.

Considering the requirements of a particular project the activation of the PMC actuator can be done with the thermo bulb or with the signal of the fire central, respectively, fire detector.

• The PMC actuators are convenient for minor loadings of skylights.
• Closing from floor is not possible.
• The PMC actuators can be used only for the natural smoke and heat exhausting (not for air ventilation). In the case when the air ventilation is required, too, they can be combined with other actuators (manual, pneumatic, electrical).

Electrical devices for the smoke and heat exhausting
The devices for the natural smoke and heat outlet, used at the opening by means of the electric engine, are usually equipped with the incorporated electric engines of 24 V. The electrical devices for the natural smoke and heat outlet always get a signal for the opening from the fire central (opening by means of the thermo bulb is not possible).

• The electrical actuators require additional source of voltage for the case of the energy failure.
• Closing from the floor is possible and in the case of the false alarm there is no need for the replacement of any elements.
• The electrical actuators can be used for the smoke and heat outlet, as well as for the air ventilation.