This is a possibility where the area con- 1 The exhaust fan would be selected to cerned has sufficient outside wall space to overcome any resistance from the exhaust accommodate the vent area necessary. The residue pressure in the Operating Mode 2 would require almost 0. The result would be a reduced c The provision of a vertical duct through quantity of supply air to the system see the building with a damper arranged to also paragraph 5.
See Fig This would tend to create a negative pressure, in the fire area, relative to the rest of the building ensuring that all Powered Vent airflow through the building is towards the fire area. Smoke will thereby be prevented from entering unaffected parts of the build- Natural Vent ing via unidentified leakage paths. Mechanical exhaust may be the only way of dealing with the high volumes of air exhaust demanded by Class B, D and E System. Damper 3. Simple Lobby. Fig 11 - Staircase With Simple Lobby.
Used only where the construction of the corridor has a fire resistance of 30 minutes or more. With the lift shaft pressurised there is no escape path for the air via the lift shaft. The answers to both these questions were Again, the formula for doing this comes from provided as a result of research work by P. Hobson and L. J Stewart in the U. These values only apply to the door types and sizes shown. Single Leaf in Frame Opening 2 m x mm 5. Double Leaf with or without 2 m x 1. Lift Door 2 m High x 8.
Although we can estimate the effective area Fig. The code of practice specify that an In this situation smoke can be held back Air Velocity of 2. ITY through the open door, out of the pres- surised space, is sufficiently high. The air supply for all these cases is usually There are two possible occasions when the greater than that required to develop the Pressurisation System has to control the 50Pa pressure requirement of the detection smoke by VELOCITY.
Both these are specified in the U. Code of Practice. BS Part 4: specifies to open doors onto the escape route, the air an air velocity of 0.
To across the closed door s onto fire floors achieve this maximum design pressure of pressure criteron. Smoke Control, and as such may be unreal. Over sizing Example: A Staircase, Fig 16 serves 6 the supply fan at the design stage can prove floors. There is a double door to outside beneficial during commissioning. Axial 5. A complete and detailed calculation proce- dure, with worked examples, is outlined in 5.
These fans must be capable With the possible exceptions outlined in of handling hot air smoke and comply with paragraph 4. The worked example in this paper employs a much simplified method of calculation de- At the time of writing neither of these specifi- veloped and used by Mr C. Moss Ref cations are in line with the high temperature categories specified in BS Part 2 or the This method is very useful when sizing Hence designers are recommended to seek and selecting the supply air fan s.
It will al- clarification from Building Control. Say 0. Door Closed Open. Staircase Accomodation Open Fig Fig 18 0. From Table D3 in BS - Part - , using average c To calculate airflow through open leakage via the floors and loose leakage walls, the door to outside with 10Pa Pressure in leakage area from the accommodation on one floor would be 0.
Door 5. This results in an 5. CHART 1 illustrates a fan engineering solu- tion to this problem viz:- Fan powered exhaust would eliminate the a The supply air fan size is determined by need for this increase in the supply fan duty. Fan selected is Woods JM Aerofoil produce zero pressure on the fire floor. This is well sure relief damper would fall to 6. However to allow for the change in the fan These take the form of fan performance working point, Point B , when all doors are charts onto which the calculated airflow re- closed the air wasted will increase to 2.
Pa - 2 Chart 1 Both fans would run to provide the nable pressure in the staircase but a requirements of Mode 3 - 9. This ing a pressure relief damper 0. CHART 4 illustrates a third possible solution the example shown the air to be wasted to the problem described in Paragraph 4. The air duty requirements of Again the fan speed is maintained elimi- MODES 1 and 2 are then achieved by reducing nating the dangers inherent with fan the pitch angle of the fan. As an added advan- tage, using Varofoil, the fan will tend to The size of the Pressure Relief Damper is correct for any unidentified leakage etc now greatly reduced, but not eliminated.
In in the staircase and system. Chart 4 This is discussed in more details under paragraph 6. The use of variable speed fans to obtain the air volume changes needs With variable speed fans this will not be expert advice. The pressure developed by the e Exhaust Air Fans must be capable of fan varies with the speed squared. They should comply with and 2, then the pressure development is re- BS Part 2 or similar testing standard.
They tem ductwork. This could lead to the fan should be manufactured by companies operating in an unstable stall condition. The reliability of the fans is under the control BS Part 4: Specifies that of fan manufacturers and building owners, STANDBY FANS and equipment be pro- the latter having responsibility for ensuring vided on all pressurisation systems de- correct and adequate maintenance.
Simply in Concept but Difficult in Practice Ref References 1. March Stewart in Buildings. December Smoke control in prote- cted escape routes using pressurisation.
Code of Practice for Fire Fighting stairs and lifts. Fire Safety Measure. February Butcher Pressurisation - Fire Surveyors October Parnell Simple in Concept Difficult in Practice. This document has been produced as a general guide and its contents should not be construed as any representation on our part as to the quality or fitness of our products for any particular purpose, nor as providing advice on the design of fire and smoke control systems. You are recommended to consult your professional advisers on matters relating to the design and installation of any such systems.
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Description: This calculation is used to pressurize ti liftwell in case of fire.
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