吸气式火灾探测器与洁净厂房

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1、专业好文档谈洁净厂房与早期火灾探测洁净厂房发展不断加快，它广泛应用于电子、生物制药、宇航、精密仪器制造及科研各个行业中，其重要性越来越被人们所认识。新建和改建的洁净厂房也越来越多。大多数洁净厂房内设有昂贵设备、仪器，而且建造费用昂贵，一旦着火，损失巨大。同时洁净厂房内人员进出迂回曲折，人员疏散困难，火灾不易发现，消防人员难以接近，防火有一定的困难。为达到室内得净化级别，洁净室内对气流、空间大小、换气率都有较高的要求。火灾后若一旦关闭净化空调系统，即使再恢复也会影响洁净度，使其达不到工艺生产要求而造成损失。而且，中断生产造成的损失也无法弥补。洁净室内一般空间较大、气流速度高，普通的感烟探测器对烟

2、雾探测有很大的困难。所以，洁净室内的烟雾探测既重要又困难。常规的火灾探测器系统往往不能有效的发挥作用，因此采用早期火灾探测及报警技术克服洁净室内高气流、大空间探测难度达到火灾极早期报警，最小化火灾损失的目的，甚至无损失。目前，国内的消防工程中应用的早期火灾探测及报警技术产品主要来自国外，有澳大利亚的Xtralis 公司的ICAM火灾探测器和公司的火灾探测技术、英国的公司的火灾探测技术。国际上，澳洲火灾防御中心、澳大利亚国家防火委员会、美国国家火灾防护委员会都有对早期火灾报警的阐述，并有推荐使用早期火灾探测报警技术的建议。以Xtralis公司的ICAM火灾探测器为例：系统通过高效抽气机，主动、连

3、续不断的在防护区内的空气吸入采样管，然后经采样管到达双级过滤器，其中经第一级过滤后，作为空气样本进入系统探测腔，用于分析和测定烟雾含量。经过的二次过滤后的空气用来冲洗探测腔内的光学元件表面，确保设备正常工作和延长使用寿命。探测腔内有一个稳定的激光源，烟雾离子使激光发生散射，散射光使高灵敏度的光接收器产生信号。经过系统分析，完成光电转换。烟雾浓度值及其报警等级由显示器显示出来。火灾都有一个酝酿发展的过程，可分为四个阶段：第一阶段，火灾起始阶段，存在人眼看不见的很微弱的烟，早期烟雾探测系统工作在这个阶段，可以探测到这些烟雾。这个阶段可达数小时；第二阶段，人们可以看见明显的烟雾存在，这就是离子、光电

4、感烟探测器工作的阶段。这个阶段离明火有数分钟至数十分钟；第三阶段，阴燃聚集的热量导致物质出现有焰燃烧，火焰探测器可探测阶段；第四阶段，高温强热阶段，温度上升数十度乃至上百度，这就是感温探测器、线型定温探测器工作范围。早期火灾探测报警系统与传统感烟式火灾探测系统在探测原理、采样方式、探测灵敏度、抗干扰能力、适应环境等方面存在较大的差异，两种系统之间的性能比较如下表所示。传统感烟式火灾探测系统与早期火灾探测系统的性能对比项目传统感烟式火灾探测系统早期烟雾探测器系统离子光电探测原理火灾后烟雾扩散至探测器并达到一定浓度才能实现探测和报警，属于被动式探测。一般采用光电式组件或放射源，单向模拟量可寻址技术

5、。主动抽取监测区域的空气，只要空气中含有火灾后产生的烟尘，就能及时探测并报警，属于主动式探测；一般采用激光前向散射技术和人工神经网络智能技术。采样方式利用烟雾的热上升特性；只有烟雾上升达到或超过探测器安装高度时，才能在烟雾检测室形成烟雾聚集，反映烟雾浓度大小。主动抽气式烟雾探测：通过抽气管路和取样孔的有效布置，能够克服房间高度的影响，将火灾初期产生的微量烟雾吸取到烟雾检测室内，对微量烟雾做出灵敏反映。探测部件镅241放射源，一个收集极红外发光管光接收管高稳定激光源，二个光接收器，三维立体图像分析测量方式相对测量绝对值测量，即对环境烟雾量的实时测量报警方式两级报警可设四级报警灵敏度5%obs/m

6、20obs/m；当产生火灾报警器报警时，火灾已经达到一定程度，扑救难度也增大。灵敏度由人工设定。0.001%obs/m20obs/m；选择同的烟阀值设置四个报警级。当探测器报警时，留给值班人员控制和扑灭火灾的时间十分充足；可设置三个可调的灵敏度等级，灵敏度由机器自动设定，人工仅设定误报率。抗干扰能力控制器和探测器之间相连的电源线和信号线较长，易形成天线效应，感应空间的电磁波；尤其是在通信、计算机等强电磁干扰区域，轻则影响探测器和控制器之间的信号传输，重则可能损坏控制器和探测器的内部组件。采样管道、取样孔等组成，无需走电线，所有电子组件都在系统探测器机壳内，不易受到外界电磁场干扰，可用于易燃易爆

7、场所、超强电磁辐场所、微波室、正负电子对撞机房、油库和军火库等。安装维护使用一定时间必须进行清洗和标定，维护工作量大，费用较高。采样管网和主机无电气连接，只需定期清除过滤网灰尘，维护工作量小，无需费用。适用范围点型感烟式探测器适用于办公室、宾馆客房等建筑环境当中，在特殊场所和工业环境无法使用。适用于通信机房、计算机机房、洁净厂房、高气流地方、电缆隧道、发电厂等环境中。组网能力一般独立组网，部分产品可以通过接口与计算机互连。可独立组网，也可由接口与计算机联网，或者通过继电器开关量接口与其他系统联网；并具有黑匣子功能，能记忆20000条信息。抗环境气流影响受气流环境影响大，要求气流速度不大于米秒，

8、在许多强气流环境中无法探测报警。不适合黑烟及高频电磁干扰强的场合，同样在许多强气流环境中无法探测报警。不受气流环境影响，可用于具有大型环境空调机组的计算中心、程控机房等环境，以及室内空气流动强烈，感烟探测器无法使用的环境。光学器件的清洗传统光电感烟探测器长时使用，其光学器件上会布满灰尘，使灵敏度下降，甚至失效，必须由人工逐个检测清洗，工作量大且损坏器件。借鉴主动抽气式原理，利用抽进并过滤的空气对光学元件不断的进行清洗，使光学元件始终保持最佳工作状态，不用人工清洗。比较可以看出：第一，普通感烟感温探测器工作至少都在火灾第二阶段之后，其灵敏度一般在减光率米，ICAM的灵敏度高达0.001减光率米，

9、是普通感烟探测器的2000倍。试验中得知：普通探测器报警时，烟雾已经弥漫了整个保护区，虽然报了警，但留下处理火灾的时间不多，错过了将火灾扑灭最佳时机。即使联动了灭火设备，也已造成财产和人员不同程度的损失。ICAM早期火灾探测报警系统在火灾第一阶段就可以探测到火灾起始的烟雾，并分四级进行报警，分别为一级预警、二级行动提示、三级临界火警（工作在火灾第一阶段）、四级火警（工作在火灾第二阶段）。值班人员可以有足够的时间来查找火源，控制火情发展和蔓延，从而确保厂房内工艺设备不会因火警而引起生产中断，避免了火灾带来的损失。第二，ICAM早期火灾探测系统不被洁净室中高气流影响，甚至可在风管中对空气进行采样收

10、集，分析烟雾浓度。第三，ICAM早期火灾探测报警系统误报率低，性能可靠。消除了误报引起的连锁反应。4软件的自学习功能使误报率降至最低，甚至在设置环境参考点后可达到零误报率。第四，ICAM早期火灾探测报警系统主动采样，管网布置灵活，不受风管、灯具等影响。ICAM系统通过在尽可能早的阶段探知烟雾的存在来提供最优的防火保护。在洁净室这种空气要求关键环境里，安装较短的取样管网可保证对潜在的火灾风险有一个较早的反应时间。另一个考虑重点是单个系统的覆盖面积。单个探测器的效率与它保护的空间和通过此区域的气体交换率成正比，同样也很重要的是室外污染气流可能会通过新风进入取样管产生误报。可安装一台基准探测器进行弥

11、补，尽可能减少或消除误报。 ICAM系统在洁净室中取样位置：根据现场勘测的数据或整体设计要求，考虑保护区域大小（如房间长、宽、高、吊顶、活动地板的尺寸），保护区域的环境状况（如空调的通风口、回风口位置、空气流动的路径及可能产生发热生烟的部位），保护对象的位置（如设备距墙，距天花板的距离）及保护程度的等级，划分探测区域，选择探测设备，进行管网设计。早期火灾探测报警系统在早期火灾报警中有着突出的特点，只有根据不同的使用场所及保护对象合理选用该系统，才能充分发挥其报警作用。实际应用中会有许多问题有待解决，如没有相应系统设计和验收规范、系统的质量监督管理、主机仅能显示报警探测的区域，没能显示出具体探测

12、采样点，这给火灾原因调查，确定起火点造成一定的困难等。以上只是我的一些工作中的想法，欢迎同行批评指正。Editors note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced with CNN for four years, covering severe weather from tornadoes to typhoons. Follow him on Twitter: jnjonesjr (CNN) - I will always wonder what it was like

13、 to huddle around a shortwave radio and through the crackling static from space hear the faint beeps of the worlds first satellite - Sputnik. I also missed watching Neil Armstrong step foot on the moon and the first space shuttle take off for the stars. Those events were way before my time.As a kid,

14、 I was fascinated with what goes on in the sky, and when NASA pulled the plug on the shuttle program I was heartbroken. Yet the privatized space race has renewed my childhood dreams to reach for the stars.As a meteorologist, Ive still seen many important weather and space events, but right now, if y

15、ou were sitting next to me, youd hear my foot tapping rapidly under my desk. Im anxious for the next one: a space capsule hanging from a crane in the New Mexico desert.Its like the set for a George Lucas movie floating to the edge of space.You and I will have the chance to watch a man take a leap in

16、to an unimaginable free fall from the edge of space - live.The (lack of) air up there Watch man jump from 96,000 feet Tuesday, I sat at work glued to the live stream of the Red Bull Stratos Mission. I watched the balloons positioned at different altitudes in the sky to test the winds, knowing that i

17、f they would just line up in a vertical straight line we would be go for launch.I feel this mission was created for me because I am also a journalist and a photographer, but above all I live for taking a leap of faith - the feeling of pushing the envelope into uncharted territory.The guy who is goin

18、g to do this, Felix Baumgartner, must have that same feeling, at a level I will never reach. However, it did not stop me from feeling his pain when a gust of swirling wind kicked up and twisted the partially filled balloon that would take him to the upper end of our atmosphere. As soon as the 40-acr

19、e balloon, with skin no thicker than a dry cleaning bag, scraped the ground I knew it was over.How claustrophobia almost grounded supersonic skydiverWith each twist, you could see the wrinkles of disappointment on the face of the current record holder and capcom (capsule communications), Col. Joe Ki

20、ttinger. He hung his head low in mission control as he told Baumgartner the disappointing news: Mission aborted.The supersonic descent could happen as early as Sunday.The weather plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph,

21、 with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even high

22、er than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause), he can expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet (22.7 miles/36.53 kilometers). H

23、ere, Fearless Felix will unclip. He will roll back the door.Then, I would assume, he will slowly step out onto something resembling an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, hell be traveling fast, so

24、 despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water

25、, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes its not needed. Instead, he plans to dep

26、loy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even i

27、f everything goes as planned, it wont. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,620 meters).It might not be the moon, but Kittinger free fell from 102,800 feet in 1960 - at the dawn of an infamous space race that captured the hearts of many. Baumgartner will attempt to break that record, a feat that boggles the mind. This is one of those monumental moments I will always remember, because there is no way Id miss this.