NATURALLY-VENTILATED SMOKE SHAFTS: ACCEPTABLE DEPARTURES FROM PRESCRIPTIVE CODES

摘要

The prescriptive recommendation for the design of fire-fighting shafts is covered by Approved Document B to the Building Regulations (AD-B). This simply calls up Section 2 of British Standard 5588-5. The performance of the prescribed smoke ventilation shafts (whether of the open-bottom type or of the closed-bottom "BRE" type) depends amongst other factors on the wind and on the temperature of fire gases reaching the shaft. This makes it effectively impossible to calculate the effect of the prescribed shaft without resorting to expensive and time-consuming computer modelling, as well as to considering wind frequency and direction in a statistical manner. The practical fire engineer is often faced with constraints imposed by the building such that one or more of the prescribed limiting dimensions cannot be achieved. He or she would like to be able to adopt an "Alternative Approach" to satisfying the regulatory requirements, as is permitted by AD-B and by British Standard BS 5588-5.