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1、 Estimates of the Operational Reliability of Fire Protection SystemsFor the past three years,the National Institute of Standards and Technology (NIST) has been working to develop a new encryption standard to keep government information secureThe organization is in the final stages of an open process

2、 of selecting one or more algorithms,or data-scrambling formulas,for the new Advanced Encryption Standard (AES) and plans to make adecision by late summer or early fallThe standard is slated to go into effect next year Richard W. Bukowski,P.E. Senior Engineer MST Building and Fire Research Laborator

3、y Gaithersburg,MD 20899-8642 USA Edward K. Budnick,P.E.,and Christopher F. Scheme1 Vice President Chemical Engineer Hughes Associates,Inc Hughes Associates,Inc. Baltimore,MD 21227-1652USA Baltimore,MD 2 1227-1652USA INTRODUCTION BackgroundFire protection strategies are designed and installed to perf

4、orm specific functions. For example,a fire sprinkler system is expected to control or extinguish fires: To accomplish this,the system sprinklers must open,and the required amount of water to achieve control or extinguishment must be delivered to the fire location. A fire detection system is intended

5、 to provide sufficient early warning of a fire to permit occupant notification and escape,fire service notification,and in some cases activation of other fire protection features (e.g.,special extinguishing systems,smoke management systems). Both system activation (detection) and notification (alarm

6、) must occur to achieve early warning. Construction compartmentation is generally designed to limit the extent of fire spread as well as to maintain the buildings structural integrity as well as tenability along escape routes for some specified period of time. In order to accomplish this,the constru

7、ction features must be fire “rated” (based on standard tests) and the integrity of the features maintained. The reliability of individual fire protection strategies such as detection,automatic suppression,and construction compartmentation is important input to detailed engineering analyses associate

8、d with performance based design. In the context of safety systems,there are several elements of reliability,including both operational and perfornzzsance reliability. Operational reliability provides a measure of the probability that a fire protection system will operate as intended when needed. Per

9、formance reliability is a measure of the adequacy of the feature to successfully perform its intended hnction under specific fire exposure conditions. The former is a measure of component or system operability while the latter is a measure of the adequacy of the system design. The scope of this stud

10、y was limited to evaluation of operational reliability due primarily to the form of the reported data in the literature. In addition to this distinction between operational and performance reliability,the scope focused on unconditional estimates of reliability and failure estimates in terms offail-d

11、angerous outcomes. A discussion of these terms is provided later in the paper. Scope This paper provides a review of reported operational reliability and performance estimates for (1) fire detection,(2) automatic suppression,and to a limited extent (3) construction compartmentation. In general,the r

12、eported estimates for fire detection are largely for smoke detectiodfire alarm systems; automatic sprinklers comprise most of the data for automatic suppression,and compartmentation includes compartment fire resistance and enclosure integrity. It should be noted that in some cases the literature did

13、 not delineate beyond the general categories of “fire detection” or “automatic suppression,” requiring assumptions regarding the specific type of fire protection system. Several studies reported estimates of reliability for both fire detection and automatic sprinkler system strategies. However,very

14、little information was found detailing reliability estimates for passive fire protection strategies such as compartmentation. A limited statistical based analysis was performed to provide generalized information on the ranges of such estimates and related uncertainties. This latter effort was limite

15、d to evaluation of reported data on detection and suppression. Insufficient data were identified on compartmentation reliability to be included. This paper addresses elements of reliability as they relate to fire safety systems. The literature search that was performed for this analysis is reviewed

16、and important findings and data summarized. The data found in the literature that were applicable to sprinkler and smoke detection systems reliability were analyzed,with descriptive estimates of the mean values and 95 percent confidence intervals for the operational reliability of these in situ syst

17、ems reported. ELEMENTS OF RELIABILITY ANALYSIS There is considerable variation in reliability data and associated analyses reported in the literature. Basically,reliability is an estimate of the probability that a system or component will operate as designed over some time period. During the useful

18、or expected life of a component,this time period is “reset” each time a component is tested and found to be in working order. Therefore,the more often systems and components are tested and maintained,the more reliable they are. This form of reliability is referred to as unconditional. Unconditional

19、reliability is an estimate of the probability that a system will operate “on demand.” A conditional reliability is an estimate that two events of concern,i.e.,a fire and successful operation of a fire safety system occur at the same time. Reliability estimates that do not consider a fire event proba

20、bility are unconditional estimates. Two other important concepts applied to operational reliability are fuiled-safe and failed- dangerous. when a fire safety system fails safe,it operates when no fire event has occurred. A common example is the false alarming of a smoke detector. A fire safety syste

21、m fails dangerous when it does not function during a fire event. In this study,the failed-dangerous event defines the Operational probability of failure (1-reliability estimate). A sprinkler system not operating during a fire event or an operating system that does not control or extinguish a fire ar

22、e examples of this type of failure. The overall reliability of a system depends on the reliability of individual components and their corresponding failure rates,the interdependencies of the individual components that compose the system,and the maintenance and testing of components and systems once

23、installed to veri operability. All of these factors are of concern in estimating operationaz reliability. Fire safety system performance is also of concern when dealing with the overall concept of reliability. System performance is defined as the ability of a particular system to accomplish the task

24、 for which it was designed and installed. For example,the performance of a fire rated separation is based on the construction components ability to remain intact and provide fire separation during a fire. The degree to which these components prevent fire spread across their intended boundaries defin

25、es system performance. Performance reliability estimates require data on how well systems accomplish their design task under actual fire events or full scale tests. Information on performance reliability could not be discerned directly from many of the data sources reviewed as part of this effort du

26、e to the form of the presented data,and therefore,it is not addressed as a separate effect. The cause of failure for any type of system is typically classified into several general categories: installation errors,design mistakes,manufacturing/equipment defects,lack of maintenance,exceeding design li

27、mits,and environmental factors. There are several approaches that can be utilized to minimize the probability of failure. Such methods include (1) design redundancy,(2) active monitoring for faults,(3) providing the simplest system (i.e.,the least number of components) to address the hazard,and (4)

28、a well designed inspection,testing,and maintenance program. These reliability engineering concepts are important when evaluating reliability estimates reported in the literature. Depending on the data used in a given analysis,the reliability estimate may relate to one or more of the concepts present

29、ed above. The literature review conducted under the scope of this effort addresses these concepts where appropriate. Most of the information that was obtained from the literature in support of this paper were reported in terms of unconditional operationaZ reliability,i.e.,in terms of the probability

30、 that a fire protection strategy will not faiZ dangerous. LITERATURE REVIEW A literature search was conducted to gather reliability data of all types for fire safety systems relevant to the protection strategies considered: automatic suppression,automatic detection,and compartmentation. The objectiv

31、e of the literature search was to obtain system-specific reliability estimates for the performance of each type of fire safety system as a function of generic occupancy type (e.g.,residential,commercial,and institutional). Sources of information included national fire incident database reports,US De

32、partment of Defense safety records,industry and occupancy specific studies,insurance industry historical records and inspection reports documented in the open literature,and experimental data Reports on experimental work and fire testing results were utilized only when fire detection,automatic suppr

33、ession,or compartmentation strategies were explicitly evaluated. Tests of systems used for qualification,approval,or listing were also reviewed for information on failure modes. Published data from the United Kingdom,Japan,Australia,and New Zealand were included. General Studies Several broad based

34、studies were identified that reported reliability estimates for fire detection and fire suppression systems as well as construction compartmentation. These included (1) the Warrington Fire Research study 1996 in the United Kingdom,(2) the Australian Fire Engineering Guidelines Fire Code Reform Cente

35、r,19961,(3) a compilation of fire statistics for Tokyo,Japan Tokyo Fire Department,19971,and(4)results from a study of in situ performance of fire protection systems in Japan Watanabe,19791.The Warrington Fire Research study addressed the reliability of fire safety systems and the interaction of the

36、ir components. A Delphi methodology was used to develop discrete estimates of the reliability of detection and alarm systems,fire suppression systems,automatic smoke control systems,and passive fire protection (e.g.,compartmentation). The Australian Fire Engineering Guidelines were developed as the

37、engineering code of practice supporting the new performance-based Building Code of Australia. Following the methods in this guide,building fire safety performance is evaluated for smouldering,flaming non-flashover,and flaming flashover fires. The performance (ie,probability of detecting,extinguishin

38、g or controlling a fire event) of fire safety systems is predicted,accounting explicitly for the operational reliability of the particular system. Reliability estimates from an expert panel rather than from actual data are provided in the Guideline for this purpose. Finally,operational reliability d

39、ata were reported in two separate studies in Japan. One study involved evaluation of fire incident reports from the city of Tokyo during the period from 1990 to 1997 Tokyo Fire Department 19971. The other study involved review of fire incident reports throughout Japan during an earlier time period e

40、nding in1978 Watanabe 19791.Table 1provides a summary of the reliability estimates provided in these studies. Significant differences exist in the individual reliability estimates depending on the parameters used to develop these estimates. Depending on the required accuracy in predicting future ope

41、rational performance of fire protection systems,dependence on the range of estimates from these studies could significantly alter the results. In addition,the uncertainty associated with a single estimate of reliability or the existence of potentially important biases in the methods used to derive t

42、hese estimates may limit their direct usefulness in addressing either operational or performance reliability of fire protection systems. NA= Not AddressedTable 1. Published Estimates for Fire Protection Systems Operational Reliability(Probability of Success (YO)Review of Available Reliability Data D

43、ue to the limited applicability of the reliability estimates published in the general literature,the literature review was extended in an effort to (1) develop an improved understanding of the elements of each of the three strategies under consideration that influence reliability,and (2) identify an

44、d evaluate quantitative data regarding individual system operability and failure rates. Automatic Suppression Systems (i.e.,sprinkler systems) Table 2 provides a summary of reported operational reliability estimates from several studies that evaluated actual fire incidents in which automatic sprinkl

45、ers were present. As a group,these studies vary significantly in terms of the reporting time periods,the types of occupancies,and the level of detail regarding the types of fires and the sprinkler system design. The estimates presented in Table 2 generally indicate relatively high operational reliab

46、ility for automatic sprinkler systems. While some of the references include fire “control” or “extinguishment” as part of the reliability assessment,the reported data were not consistent. Therefore,operational reliability was assumed to be limited to sprinkler operation. The estimates also indicate

47、a range of values,suggesting that it would be inapprota sources and general uncertainty associated with combining data from different databases. Automatic fire extinguishing system (sprinkler system)Table 2 summarizes some studies estimate that the evaluation of the operational reliability of automa

48、tic sprinkler system,fire fighting actual fire incidents. As a group,these studies report very different in time period,type of housing and level of detail related to the type of fire and sprinkler system design. Table 2 shows the spray system operational reliability estimates are generally relative

49、ly high,while some studies the failure of the fire control or fire,as part of the assessment of reliability,but the reports data is not consistent. Therefore,the operational reliability assume that the operation is limited to spraying. assessment should also show the value range,suggesting not to us

50、e the deviation of a spray system reliability without attention to data and combining data from different databases uncertainty sources. Table 2 of the original budget by the reliability estimates range from 81.13% to 99.5% Taylor the low value of m Taylors study and some kook overestimated (87.6%)

51、report that these significant deviation the data used in these studies. In both studies,the number of fires is very small,and in the database does not distinguish between automatic fire extinguishing systems and other fire-fighting system. The final 99.5% of the may bee and marry at reported high es

52、timates reflect a spray system in the inspection,testing and maintenance of a rigorous and well documented.The data obtained from the spray system,another important limitation is that most of the Automatic Sprinkler System records sprinkler accident. In these studies,very limited accident data with

53、reference to the rapid response or a suitable water jet technology. Assess the reliability of the appropriate sprinkler system should be particularly concerned about several factors,including (1) allows coverage within,(2) lower water supply capacity,(3) remote control or alarm systems have great po

54、tential in the fire . Based on this,there are other factors related to these technologies (such as maintenance level) can directly affect the operational reliability of these types of Automatic Sprinkler System. In addition,you also need to resolve these problems,the system data,but based on later o

55、bservations and general housing is generally less likely to maintain normal,some designed to ensure the residence what spray system reliability may be reduced. .Fire detection or alarm systemsTable 3 provides an overview of a report on the operational reliability for residential systems analysis to

56、assess the average probability and 95% confidence intervals are estimated based on data provided by HALL 1955. The scope of the average reliability estimates ranging from 68-88%. Figures are consistent with those provided by the standards with Toby Delphy. Institute reliability. However,the general

57、scope of the 95% confidence interval 66-90%.Table 3: Analysis of the reliability of smoke detectors HALL,1955The fire district to rely on various types of equipment such as: doors (including fixed equipment),wall,floor / ceiling penetration holes,windows,fire shutter,smoke materials and buildings. W

58、hen the fire district is considered to be the focus in the fire plan,in the literature,there is little data that the individual components of the operating role in the fire district. The single is mentioned for the building assessment and operational reliability WARRIGTON research and the Australian

59、 Fire Engineering Index. These assessments are based entirely on expert judgment. Therefore does not provide more in-depth analysis.Automatic sprinkler systems analysisOn Table 2,the sprinkler system reliability analysis is to analyze according to the type of each live. It should be noted that only

60、one source MILNE,1959 on the reliability of public buildings and residential housing estimates,and these early data do not provide the reliability of the data of modern residential sprinklers. The distribution histogram of Figure 1 lists the reliability estimates for each housing type. Average and 9

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