建筑防火设计外文翻译

建筑防火设计外文翻译内容摘要：

ons described in the introduction are now considered. 3 FIRE WITHIN BUILDINGS Fire Safety Considerations The implications of fire within the occupied parts of the office building (Figure 1) (Situation 2) are now considered. Fire statistics for office buildings show that about one fatality is expected in an office building for every 1000 fires reported to the fire brigade. This is an order of magnitude less than the fatality rate associated with apartment buildings. More than two thirds of fires occur during occupied hours and this is due to the greater human activity and the greater use of services within the building. It is twice as likely that a fire that mences out of normal working hours will extend beyond the enclosure of fire origin. A relatively small fire can generate large quantities of smoke within the floor of fire origin. If the floor is of openplan construction with few partitions, the presence of a fire during normal occupied hours is almost certain to be detected through the observation of smoke on the floor. The presence of full height partitions across the floor will slow the spread of smoke and possibly also the speed at which the occupants detect the fire. Any measures aimed at improving housekeeping, fire awareness and fire response will be beneficial in reducing the likelihood of major fires during occupied hours. For multistorey buildings, smoke detection systems and alarms are often provided to give “automatic” detection and warning to the occupants. An alarm signal is also transmitted to the fire brigade. Should the fire not be able to be controlled by the occupants on the fire floor, they will need to leave the floor of fire origin via the stairs. Stair enclosures may be designed to be fireresistant but this may not be sufficient to keep the smoke out of the stairs. Many buildings incorporate stair pressurisation systems whereby positive airflow is introduced into 6 the stairs upon detection of smoke within the building. However, this increases the forces required to open the stair doors and makes it increasingly difficult to access the stairs. It is quite likely that excessive door opening forces will exist(Fazio et al,2020) From a fire perspective, it is mon to consider that a building consists of enclosures formed by the presence of walls and enclosure that has sufficiently fireresistant boundaries (. walls and floors) is considered to constitute a fire partment and to be capable of limiting the spread of fire to an adjacent partment. However, the ability of such boundaries to restrict the spread of fire can be severely limited by the need to provide natural lighting (windows)and access openings between the adjacent partments (doors and stairs). Fire spread via the external openings (windows) is a distinct possibility given a fully developed fire. Limit ing the window sizes and geometry can reduce but not eliminate the possibility of vertical fire spread. By far the most effective measure in limiting fire spread, other than the presence of occupants, is an effective sprinkler system that delivers water to a growing fire rapidly reducing the heat being generated and virtually extinguishing it. Estimating Fire Severity In the absence of measures to extinguish developing fires, or should such systems fail。 severe fires can develop within buildings. In fire engineering literature, the term “fire load” refers to the quantity of bustibles within an enclosure and not the loads (forces) applied to the structure during a fire. Similarly, fire load density refers to the quantity of fuel per unit area. It is normally expressed in terms of MJ/m2 or kg/m2 of wood equivalent. Surveys of bustibles for various occupancies ( offices, reta il, hospitals, warehouses, etc)have been undertaken and a good summary of the available data is given in FCRC (1999). As would be expected, the fire load density is highly variable. Publications such as the International Fire Engineering Guidelines (2020) give fire load data in terms of the mean and 80th latter level of fire load density is sometimes taken as the characteristic fire load density and is sometimes taken as being distributed according to a Gumbel distribution (Schleich et al, 1999). The rate at which heat is released within an enclosure is termed the heat release rate (HRR) and normally expressed in megawatts (MW). The application of sufficient heat to a bustible material results in the generation of gases some of which are bustible. This process is called 7 pyrolisation. Upon ing into contact with sufficient oxygen these gases ignite generating heat. The rate of burning(and therefore of heat generation) is therefore dependent on the flow of air to the gases generated by the pyrolising flow is influenced by the shape of the enclosure (aspect ratio), and the position and size of any potential openings. It is found from experiments with single openings in approximately cubic enclosures that the rate of burning is directly proportional to A h where A is the area of the opening and h is the opening height. It is known that for deep enclosures with single openings that burning will occur initially closest to the opening moving back into the enclosure once the fuel closest to the opening is consumed (Thomas et al, 2020). Significant temperature variations throughout such enclosures can be expected. T。