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Impact of jet fan ventilation systems on sprinkler activation

机译：射流风扇通风系统对喷头启动的影响

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Jet fans are increasingly preferred over traditional ducted systems as a means of ventilating pollutants from large spaces such as car parking buildings. Outside of tunnel applications jet fans are considered to have limitations as means of smoke control. This is because their effectiveness is limited without side walls and they de-stratify the smoke layer. Jet fans can however, aid post-event in smoke clearance under the control of the attending fire brigade. The prudent fire mode strategy in those jurisdictions where jet fans are not used for smoke control is for the ventilation system to shut down on a fire alarm signal. The problem lies in the jet fans receiving that signal. A fire has three basic signatures; heat, smoke, and light. Large car parking buildings may be sprinkler-protected. Sprinklers operate on the heat signature. A jet fan is assumed to disrupt this signature by forcing the plume of heat downstream and diluting that plume with cool air. This may delay sprinkler activation. In terms of the smoke signature, the presence of pollutants such as carbon monoxide that could be detected by a specialised detector, are the same signals that would cause a jet fan to increase its flow in normal mode. The response to a smoke signature is contradictory between the desired normal-mode reaction to speed up and the fire-mode reaction to shut down. This leaves light. Fires are very rich across the non-visible light spectra and flame detectors are an effective way to provide a fire signal independent of the normal-mode operation of the jet fans. However, the cost-benefit of installing flame detectors in addition to sprinklers is questionable. A series of detailed computational analyses are therefore undertaken to quantify the impact of the jet fans on delaying sprinkler activation on a typical car park sprinkler arrangement. This article assumes the perspective of a jurisdiction where the fire mode strategy is for the fans to shut down. However, the sprinkler delay will also be of interest where the fire mode strategy is to continue operating. Once sprinkler activation had occurred a fire signal is assumed to have been generated to shut down the jet fans. Separate evaluations can then be made as to whether the delay was acceptable or not, dependent upon to the specific building geometry. The results indicate that for a fast-growing design fire, sprinkler activation occurred at ～180s with the jet fans off and at ～210s with them on: an increase of ?30s. A separate analysis was undertaken for the case-specific egress safety margin. Comparing the two, it was concluded, that the impact of jet fans upon sprinkler activation was not significant. It was further established that the smoke disturbance due to the jet fan flow did not adversely affect the visibility for those escaping.
机译：喷气风扇比传统的管道系统越来越受欢迎，它是一种从大型空间（如停车场）排放污染物的方法。在隧道之外的应用中，喷气风扇被认为是限制烟气的手段。这是因为它们的有效性在没有侧壁的情况下受到限制，并且它们使烟雾层分层。然而，喷气飞机的风扇可以在参加的消防队的控制下帮助事后清除烟雾。在那些不使用喷气风扇控制烟尘的辖区，谨慎的火灾模式策略是使通风系统在发生火灾警报信号时关闭。问题出在喷气风扇接收到该信号。火灾具有三个基本特征。热，烟和光。大型停车场建筑可能受到洒水保护。洒水喷头以加热信号运行。假定喷气风扇通过迫使下游的热羽流并用冷空气稀释该羽流来破坏此特征。这可能会延迟喷头的启动。就烟雾特征而言，可以由专门的检测器检测到的污染物（例如一氧化碳）与会导致喷气风扇在正常模式下增加其流量的信号相同。对烟雾签名的响应在所需的加速正常模式反应和熄火模式反应之间是矛盾的。这留下了光。火焰在不可见光谱范围内非常丰富，火焰探测器是一种有效的方式，可提供独立于喷射风扇正常模式运行的着火信号。但是，除了喷头外，安装火焰探测器的成本效益值得怀疑。因此，进行了一系列详细的计算分析，以量化喷射风扇对典型停车场洒水装置上的延迟洒水装置启动的影响。本文假设了一种以防火模式策略关闭风扇的辖区。但是，在火灾模式策略要继续运行的情况下，洒水延迟也会引起人们的兴趣。一旦发生喷水灭火动作，就假定产生了火警信号，以关闭喷射风扇。然后可以根据特定的建筑物几何形状，对延迟是否可以接受进行单独评估。结果表明，对于快速增长的设计火灾，喷头关闭时，喷头启动在〜180s处发生，喷头风机在〜210s时发生喷头激活：增加了30s。针对特定案例的出口安全裕度进行了单独的分析。比较两者得出的结论是，喷射扇对喷水器启动的影响并不显着。进一步确定，由于射流风扇气流引起的烟雾扰动不会对逃逸者的可见度产生不利影响。

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