Smoke and heat extraction systems RWA and natural smoke extraction systems (NRA)
Smoke and heat extraction systems (SHEV systems) are an important part of structural fire protection. They ensure that in the event of a fire, smoke and fire gases are discharged from inside a building to the outside. A distinction must be made between natural and mechanical RWA. Natural smoke extraction systems (NRA) ensure that the combustion products can escape through ceiling or wall openings. Mechanical smoke exhausts are installed with special smoke exhaust fans or smoke extraction fans when there is no possibility to use natural systems. The systems are triggered either manually or automatically by fire detectors or fire alarm systems.
How RWA systems work
In the event of a fire, in addition to the flame, there is primarily smoke, heat and rising combustion gases. These rise up in the room and form a layer below the ceiling, which can lead to complete smoke in the rooms and buildings. The smoke outlets ensure a kind of “natural” smoke behavior, so that the fire’s own thermals can continue. The air supply openings in the lower area ensure a kind of chimney effect, which provides the necessary compensation (smoke extraction).
Tasks of RWA systems
– Keep escape and rescue routes low in smoke
– Facilitate firefighting
– Delay or prevent the spread of fire
– Protect goods, facilities and buildings
– Consequential damage from fire gases
– Faster evacuation of people and animals
– Environmental protection: Minimization of extinguishing agents and thus the damage caused by extinguishing
Electrical, pneumatic and pyrotechnic SHEV systems
Different systems for different requirements are possible. With the system parts, any type of windows, flaps and light domes can be operated automatically and manually, electrically or pneumatically. The decisive consideration when installing an RWA is the type of system: systems that can only be opened in the event of a fire, or systems that can also be used for general ventilation.
Regardless of any power supply, the pneumatic RWA has the advantage of being functional even in the event of a total power failure. These are operated (triggered) via alarm boxes with CO2, or with a so-called thermal tripping device (TAG), which e.g. is provided with a glass bulb or with a fusible link and is triggered independently at approx. 68°C under the dome. Here, too, a CO2 bottle is connected to the thermal release device, which ensures that the dome can open independently. Due to the low use of materials, the pneumatic RWA is the most maintenance-friendly solution.
Electrical RWA can either be triggered manually with push-button detectors or automatically with smoke detectors. The advantage of the electrical RWA is that it is also operated by the emergency batteries in the event of a power failure. In addition to the protective function in the event of fire, this system can also be used for daily ventilation. The system can also be equipped with a wind and rain monitor, which automatically closes the ventilation flaps as soon as it suddenly rains or winds. Retrofitting in existing systems is usually possible
Also known as pyrotechnic rapid openers, these are smoke vents with explosive gas-operated rapid openers. Since improper handling poses an extremely high risk of injury and even death, special care must be taken here. Handling of pyrotechnic Rasant openers is only allowed for authorized specialists. The person carrying out the work should be able to provide evidence of professional training and instruction for pyrotechnic RWA.