11-04-2013, 03:37 PM
SMOKE EXTRACTING SYSTEMS IN BUILDINGS
SMOKE EXTRACTING SYSTEMS.docx (Size: 400.94 KB / Downloads: 43)
ABSTRACT:
Smoke extraction methods prescribed in the Building Standards Law, it cannot be said that a rational method for determining the air supply rates required for achieving the smoke control goals has been well-established. As a result, computer simulation models are usually used as the means to estimate the air supply rates. It may not be inappropriate but it causes some difficulties for ordinary designers to try this smoke control system. This paper proposes a practical design method of vestibule pressurization smoke control systems. This method comprehensively covers the fire scenarios corresponding to every stage of evacuation, namely fire room evacuation, fire floor evacuation and whole building evacuation. The required rates of air supply are determined to meet all the criteria imposed to verify the safety requirements at these three stages of evacuation. This method is expected to help designers and engineers easily understand what and how to do to rationally and effectively design the smoke control system and to help building officials or whoever may concern with approval of the system know how to check its compliance.
INTRODUCTION:
While only smoke extraction methods are prescribed in the existing government orders associated with the Building Standards Law. Particularly for high-rise office buildings, for which protection of staircases by vestibules is required by the government order. This popularity seems to be attributed particularly to that the system allows more flexibility of floor layouts and more rentable space than the smoke extraction method. In addition, this smoke control system often accompanies pressurization of elevator shafts which aims at preventing smoke spread through the shafts.
OUTLINE OF THE SYSTEM:
In this study, we consider high-rise office buildings where “special evacuation staircases” (smoke proof towers) are required. Fig. shows a typical floor plan of such office buildings. Each floor has an office room, a corridor, a vestibule, a passenger elevator bank, a staircase and a fire elevator bank. These spaces are identified by R, C, L, E, Sand F respectively, and the outdoor space is identified by letter O in this paper.
COMPONENTS OF A SMOKE EXTRACTION SYSTEM:
An SHE safety drive is needed to open and close the SHE openings. This can be a servo powered 24V drive, such as a spindle drive, chain drive or rack-and-pinion drive.The discharge air and fresh air flaps can be quickly opened using an electrically or pneumatically driven gas spring system. This system is not, however, suitable for daily ventilation.
A pneumatic cylinder opens the flap using compressed air or CO2 gas. The SHE control centre controls the SHE drives. It registers fire alarms, monitors malfunctions and controls the ventilation functions. Integrated batteries provide emergency power to maintain operational readiness for 72 hours in the event of a power outage. The pneumatic operating station is fitted with CO2 capsules. The system is triggered by breaking the glass and activating the button.
Manual fire alarms report a manual activation of the SHE system. Signal lamps display the states "Operational readiness", "SHE activation" and "Malfunction". Automatic fire alarms detect fires independently. The choice between manual or automatic fire alarm is determined, amongst other factors, by the fire protection concept and local conditions. An anemometer that records wind speed and direction ensures that only the flaps on the lee side are opened to extract smoke. The measured values are analyzed by the SHE control Centre.
NATURAL SMOKE EXTRACTION:
Since the earliest days of civilization, fire and smoke have not only been two of "man's" most important tools; they have also been two of our biggest enemies. The growing numbers of fire catastrophes, which not only cause enormous damage to property but also cost innumerable human lives, are the reason why firefighting is growing in importance. Smoke and heat extraction Systems play a central role in fire protection concepts, since it is not possible to fully preventfiresinbuildings.
Death from fumes is caused by the fatal toxic components of smoke. At the same time, the so-called "corrosive components" cauterize both the lungs and respiratory tract when inhaled. The combination of these two effects usually causes the poisoning and considerable internal injuries suffered by fire victims.
SMOKE AND HEAT EXHAUST VENTILATION SYSTEMS-SMOKEVENTS:
Also known as "SHEVs" (smoke and heat exhaust ventilators), this is the generic term for natural and powered smoke extract systems, sometimes known as fire or smoke vents. In general, these remove the smoke from the building allowing low level escape routes to be kept clear of smoke.Smoke caused by fires is sometimes highly toxic and can lead to long-term diseases or even death if inhaled. The smoke must be removed from the risk zone with the aid of technical systems.
SMOKE EXTRACTION ACTUALLY WORKS:
Natural smoke extraction makes use of thermal lift - using fresh air vents close to ground level and discharge air vents that are preferably located up near or in the ceiling - to bind the smoke into a stable layer of fumes contained by a borderline above the area in which people are located. The black toxic layer of fumes is contained above this borderline, the layer offumescontaininglesssmokeisbelowit.When using this method of smoke extraction, care must be taken to prevent swirling air at the borderline between the layers of fumes since this could cause the toxic layer of fumes to descend into the area containing less smoke.
CONCLUSION:
This paper intended to propose a logically clear and technically simple method to solve the problems. As a result, this method has thefollowing advantages: all the fire scenarios including evacuation at fully developed fire can betaken into account for fire safety criterion, the base of pressure difference criterion for smoke stopping is logically and technically clear, and the procedures of this method consisting of simpleformulas make it possible to check the contents of calculation and the verification of safetyrequirement even for ordinary designers or building officials. Smoke ventilation systems should be regularly tested and adequately maintained.