Test of fire detection algorithms using artificially generated events

The paper proposes a test method that is particularly suitable for the test of the false alarm rejection features of detection algorithms. It describes how to generate signal events artificially, which are similar to those occurring in practice, and thus may or may not cause false or unwanted alarms. The generated events are of random nature, i.e. the signal shape, amplitude and duration of the events is randomly varied and the points in time, where these events occur, are randomly selected according to a well defined signal model. A set of parameters controls the event density, the probability for the duration of events, the fluctuation and the full dynamic range.The whole signal model uses only one pseudo-random generator and generates a modified “random walk process”. Thus, it is either possible to reproduce with the same set of parameters for the signal model the same random sequence of events or, alternatively, to generate different random signal sequences using a different seed for the pseudo-random generator. The test procedure is carried out in the form of a computer simulation in time-lapse mode, and thus requires the detection algorithm to be available as a C-program.     

Fire detector systems with ‘distributed intelligence’ the pulse polling system

Well over a million fire detectors are currently in use in the Federal Republic of Germany. Provided they are correctly installed and efficiently maintained, they detect fires reliably at a very early stage. At the present time, the false alarm rate equals about 1% of the number of installed detectors per annum. This false alarm rate must be at least proportionately reduced as further detectors are installed.

Since it is scarcely possible to improve tried-and-tested detector designs, the employment of higher-grade detector signal processing methods suggests itself.

However, ‘more intelligent’ detector signal processing using microprocessors calls for an entirely new fire detection system structure: detectors which independently ‘decide’ whether an alarm criterion is met and then initiate an alarm are replaced by sensors which continuously transmit their measured values to the ‘intelligence’ panel for evaluation. Passive panels which simply receive alarm signals from activated detectors and indicate these or transmit them to the fire brigade are replaced by active processors using permanently improved algorithms for the detection of real fires.

A structural change of this type is possible provided the positive — and the customary — characteristics of the conventional technique are not lost, viz. two-wire lines between detector and panel, simple installation and handling, easy detector replaceability, low cost, etc.

The pulse detector technology is described in detail; it combines the simplicity of conventional fire detection systems with new characteristics, e.g. identification of individual detectors, permanent functional check of all connected detectors, automatic notification of maintenance requirement prior to a slowly developing fault (e.g. such as that caused by corrosion or contamination), uniform response sensitivity unaffected by drifting from the operating points of the detectors and, above all, greater protection against false alarms.     

Control system simulation — computer control

The practical difficulties associated with digital computer simulation of computer control systems are investigated. The degree of detail necessary for adequate simulation, the problems introduced by the discrete-time nature of the control action and the selection of suitable values for the parameters of the model of the controller are discussed. The simulation of both conventional and self-tuning microprocessor controllers are examined. A number of difference equation models of discrete-time ‘proportional plus integral plus derivative’ control laws are presented and two basic types of simple self-tuning control algorithms are described. Future developments in the simulation of computer control systems are reviewed.     

Background signals from fire detectors: Measurement, analysis, application

A research programme has been running in excess of three years monitoring and recording the signals produced by individual heat and smoke sensors in a medium sized analogue addressable fire detector installation. The data has been recorded on 40 Mbyte Winchester discs which have been connected via electrically isolating circuitry to the same scanner interface as the Automatic Fire Detection Systems computer. One 40 Mbyte capacity disc is capable of collecting and recording all of the scan data continuously, at the system scan rate, for a period of 5 days. A second smaller analogue addressable system has been monitored by a microcomputer event logging system for a period of approximately 4 years.

Various forms of statistical treatment analysis have been carried out on the data. The preferred form appears to be ‘return period analysis’—a cumulative logarithmic frequency analysis showing the number of times threshold signal levels have been exceeded. The latter technique enables a relationship between threshold analogue signal levels and frequency of false alarms to be predicted. The measurement and analysis techniques developed are applicable to the commissioning of both new installations and extensions to existing installations. The techniques enable potentially troublesome sensor points to be identified before they can cause false alarms. The approach can reduce the number of false alarms and may thus enable the sensitivity of parts of the system to be enhanced.     

Thermal response of sprinklers part II. Characteristics and test methods

This paper presents an introduction to the measurement of the thermal response characteristics of sprinklers and aspects of testing which are relevant to performance requirements for specific applications, e.g., for life safety and for protecting high-rack storage. Comparisons are made between test results and ranking orders derived from two methods; the ‘rate-of-rise’ test developed in the U.K. and the ‘plunge’ test as developed in the U.S.A. This paper describes the background to both tests and presents explanations for the differences in the results obtained from each method. The rate-of-rise test is suggested for sprinkler classification; the plunge test for measuring consistency in operation.     

A computational intelligent fuzzy model approach for excavator cycle time simulation

The tracked hydraulic excavator is one of the most versatile and widely utilised piece of earthmoving equipment. In many instances, the ‘excavator’ represents the first choice of earthmoving plant for both construction managers and estimators, since when properly employed (i.e. with a competent operator and in an appropriate working environment), it offers high production rates at economical cost. Nonetheless, predicting machine production performance is difficult; given the typical multiple operational parameters (e.g. machine weight, machine configuration, ground conditions, operator ability) that can apply. Consequently, determination of accurate cost estimates and predicted contract durations are subject to considerable inaccuracy, especially where a significant amount of site work is needed.

To address this inadequacy, this paper presents a computational intelligent ‘fuzzy’ model with the ability to forecast excavator cycle time. In this context, a cycle is defined as one complete revolution, from ‘place empty bucket in dig material’ through ‘fill bucket’, ‘move charged bucket to target’, ‘empty charged bucket’ and ‘return bucket to dig material’. The developed model is based upon 70 separate cycle time observations obtained from four plant manufacturers. These data provide a representative spread of machine cycle times since they include a range on a continuum from optimum to adverse operational parameters. Tests on the derived model identified that its accuracy was acceptable; but the accuracy could be improved using larger samples and a more comprehensive and exhaustive range of variables to predict machine cycle time.     

Coupled dynamics of tensioned buoyant platforms and mooring tethers

A mathematical model is presented of the coupled dynamics of a tensioned buoyant surface platform and the lateral dynamics of its taut mooring tethers. A finite element model of the lateral mooring tether dynamics is extended to take account of nonlinear square law fluid damping by a simple global ‘whole tether’ linearization and an alternative computationally more expensive ‘element-by-element’ linearization scheme. The resultant finite element model is combined with the surface platform dynamic analysis and the coupled dynamic model is used to investigate the effects of water depth, surface platform mass and tether mass per unit length on the tether displacements and bending stresses as well as the resultant surface platform displacements. The results show that the bending stresses induced in the tethers due to their dynamic motions are quite small and that the tether dynamics only affect the motion response of the platform appreciably if the tethers are long (1500 m or more), have a large mass per unit length and have a relatively low tension; or if the platform mass is relatively small. It was also found that the additional computing time required for the local ‘element-by-element’ equivalent linearization was not matched by the small improvement in accuracy obtained over the global ‘whole tether’ technique.     

A probabilistic model of fire spread with time effects

The paper outlines the principal elements of a probabilistic model that analyses the spread of fire in multi-compartment buildings with respect to time. The analysis uses a graph theoretic network and an event hierarchy to determine the probability of fire spreading to different locations. The probability of fire spreading between compartments is based on a comparison of the probability density functions of the expected fire resistance and the fire severity: failure being the condition that severity exceeds resistance. The model is designed as a comparative tool to compare the performance of different fire safety strategies by calculating a ‘cost index’ for each design, based on the probable extent of fire damage in the building. The analysis gives attention to the compatibility of fire resistance and fire severity, and their conversion in real time parameters.     

Aesthetics of thin-walled structures

Thin-walled structures are assumed to include all ‘surface-acting’ structures. This is a brief review of the factors generally considered to influence our emotional and intellectual response to built forms. General problems arising from the strong forms and large plain surfaces of thin-walled structures are considered. A number of specific types are then treated under the headings of ‘bridges’, ‘shells’, ‘silos’, ‘tents’ and ‘air-supported structures’.     

Determination of effective breadth and effective width of stiffened plates by finite strip analyses

A finite strip (FS) method is presented for the numerical investigation of two design parameters — effective breadth and effective width — of stiffened plates. For the effective breadth, stiffened plates under bending are studied. Due to the transverse bending loads there is shear transmission through the plate from the stiffener which leads to a non-uniform longitudinal stress distribution across the plate width. This phenomenon, termed as shear lag, can be represented by the ‘effective breadth concept’, and has been extensively studied by analytical methods. A linear FS method is presented which utilizes the advantages of decoupling of Fourier terms on the one hand and, on the other hand, allows the treatment of both webs and flanges using a plate model. A definitely different situation exists for estimating the effectiveness of the plate breadth (or width) of plates in the postbuckling range. The ‘concept of effect width’ is based on the fact that plates with supported longitudinal edges and/or stiffeners can accept additional load after buckling under longitudinal compression, and enables the designer to evaluate the postbuckling strength of plate structures simply by using the design parameter ‘effective width’. Several formulae (most of them empirically derived) exist for an approximative calculation of the load dependent value of the effective width. A nonlinear FS method is developed and applied to the investigation of the postcritical strength of locally buckled structures. An incremental successive iterative procedure is introduced for an effective numerical analysis.     

A simulation model for fire growth on materials subject to a room-corner test

A mathematical model has been developed to simulate fire growth on wall and ceiling materials when subject to a room-corner fire test exposure. The model predicts the area of burning, the upper layer gas temperature, and the rate of energy release as a function of time. Material fire property data are developed from apparatuses described in ASTM E 1321 and E 1354. The results compare favorably to experimental data generated in Sweden for 13 materials tested. Furthermore, the model shows the sensitivity to ‘flashover’ for thin materials relative to small variations in their property data.     

The application of BS5950: Part 8 of fire limit state design to the performance of ‘old’ structural mild steels

An investigation has been carried out to extend the guidance given in the new British Standard BS5950: Part 8, on fire limit state design, to the refurbishment and fire damage reinstatement of old steel framed, buildings.

Structural mild steel produced to BS15 approximately 50 years ago was found to be generally weaker at elevated temperatures than its modern counterpart—BS4360: Grade 43A (BS EN 10025: Grade 430A). However, providing in design calculations due recognition is given to the lower yield stress of old mild steel at ambient temperature, its performance in fire will be as good as that being currently produced. For the present time, it is therefore appropriate to adopt the same relationships between strength, loading and temperature for structural members given in the new Code, with no additional penalties on fire protection thickness should this be necessary.

Fire simulation treatments on steel manufactured to BS15 demonstrated that the degradation in strength properties is in agreement with work reported earlier on ‘weak’ mild steel—BS4360: Grade 43A. The results of a similar evaluation on mild steel produced since the 1986 revision of BS4360: Grade 43A are also in line with previous work.     

Interrupted interface on the cybernetics of digital design process

From the viewpoint of Batesonian cybernetics, ‘conscious purpose’ and ‘artistic process’ are distinct ends of a spectrum of the functioning of ‘self’. The conceptual stage of the design process is essentially an artistic activity unencumbered with accuracy, dimensionality, scale, program or even tectonics, albeit all of these maybe tacitly present at the ‘back of a designer's mind’. Artistic activities involve broad mental processes that are beneath the stratum of consciousness. By definition, consciousness is selective awareness; it is linear in execution and limited in its capability to synthesize complex parameters. One of the central questions of this paper is “if artistic process requires one to abandon, or relinquish conscious purpose at the time of the generation of the work of art, and if the early stages of artistic process is a result of a vast number of ‘unconscious’ forces and impulses, then how can the computer, which demands (and thus propagates) geometric precision, focused operation and rational execution, be part of that process?” This paper will explore how, cybernetically, the computer can be ‘coupled’ with ‘self’ (via a visual interface) and the artistic process. Three specially devised conceptual design exercises—namely BlurrDesign, BlinDesign and BlitzDesign—and three corresponding “interruptive” computer interface modifications were deployed in an introduction to digital media course. The results of this study are now under consideration for their effectiveness in promoting conceptual design using the computer, and how the ‘self’ might form a cybernetic whole with the machine. The findings could have implications in design pedagogy, informatics and interface design.     

Flexural capacity of thin wall fibre reinforced cement

A method of calculating the flexural strength (cracking) of fibre reinforced cement floor and wall systems is presented. The method for flexural strength is based on non-linear stress-strain relationship at failure tension and corresponding stress distribution in section at cracking and subsequent failure. The method is verified in tests of full-scale ‘V’ and ‘U’ shaped panels made of asbestos-cement which were tested as simply supported beams designed for the construction of low cost housing and wall facades. Additional tests were performed on small sized samples to verify the mechanical properties of material used.     

Fire detection using cross-correlations of sensor signals

Experiments have been carried out to investigate the efficacy of signal cross-correlation techniques to provide early detection of fire. Cross-correlations were of the form A·B and A·B·C, where A, B and C were signals from various sensors and denotes averages of signal products over a correlation time interval, τ_c, extending from present time into the past. All signals were referenced to their baseline averages extending over a time interval, τ_B, into the past. Tests were conducted in a room, quiescent or highly ventilated, using fire sources modeled on the test fires of European Standard EN54. Various sensors responded to airborne pyrolysis and combustion products. Two complementary cross-correlations, ΔCO·ΔION and ΔCO₂·ΔT, were shown (with τ_B selected in the range 100–250 s and τ_C selected in the range 10–25 s) to be equivalent to a much more sensitive detection system than implied by the limits of the most sensitive EN54 class, where ΔCO and ΔCO₂ are referenced carbon monoxide and carbon dioxide concentrations, ΔION is the referenced output of a measuring ionization chamber, and ΔT is the referenced temperature.     

A trend-duration and gradient detector for automatic fire detection

Fire signals from sensors have a trend-duration characteristic, but such disturbance trends last only a short time. Step-shaped signals from fire sensors do not have a large trend value, although they may indicate a rapidly growing fire. Conventional trend algorithms cannot recognize the signal gradient. In this paper, a trend-duration and trend-gradient detector is proposed for automatic fire detection. The detector can distinguish fire signals from noise using a trend-duration algorithm. The fire smoke density (if smoke sensors are used) can be determined with the gradient algorithm. In order to indicate the level of the smoke density, fuzzy logic is applied to the gradient determination.     

Tangible virtuality—perceptions of computer-aided and physical modelling

Designing—giving form to new objects or environments—is largely a question of anticipating the workings of spatial and material environments, which can become ‘reality’ only by being built. Until ‘realized’, a design is essentially a figment of the designer's imagination, although his or her ideas may be laid down and conveyed to others via specialized design media. In this way, impressions of the design may be shared with clients, colleagues or other ‘actors’ in the design process.

Such products of the designer's imaging process can be relatively abstract or begin to approach future reality. Form & Media research can be ‘revealing’, stimulating insights concerning preferences, working processes and the effects of products of the designer's imagination. In the past 10 years, we have gained considerable practical experience with both virtual and tangible (scale) models. We have compared different techniques in conference workshops, within educational settings and in our Form & Media research laboratory. The research projects ranged from the development of practical techniques and working methods to protocol analyses of designing architects.

This contribution draws comparisons between different computer-aided modelling techniques, with an indication of their perspectives, making use of the experience gained from various experiments in an educational context, and will highlight the potentials for different combinations of digital and physical modelling techniques.     

受限空间火灾探测数据融合算法研究

为了实现对受限空间火灾发生情况多传感器自动探测信号处理,建立了基于CO浓度、烟气颗粒浓度、红外视频图像等多传感器探测的火灾探测数据融合分析系统.在受限空间内搭建基于多传感器火灾探测的数据融合分析实验平台.根据火灾红外视频图像的燃烧区域面积及圆形度等特征参数介绍了红外图像识别算法.在三种火灾探测方式特征参数的基础上提出了...     

Signal detection aspects in automatic fire detection

Automatic fire detectors can be considered as signal detectors for a special “signal-in-noise” detection problem. The paper uses the classical model for the measurable signal x(t) = s(t) + n(t) and gives an analysis of the signal component s(t), which is generated by the fire and which is to be detected. Using a general matched filter concept in combination with rather general properties of the fire signal component s(t), several forms of fire signal detectors can be developed which are optimum detectors in a rather general sense. These detectors are given as simple signal processing algorithms which can be realized by using a microprocessor or a special integrated electronic circuit. The efficiency of fire detectors depends very much on the behavior of the noise component n(t) which in the practical case of heat or smoke detection must be considered as highly self-correlated, in other words n(t) varies slowly with time compared with the fire signal component s(t). In this case it is nearly impossible to calculate the detector efficiency in advance for signal detection situations which may be interesting for practical cases.

In order to study the behavior and the efficiency of these detectors a Monte Carlo method has been used, and a measuring procedure has been established with suitable accuracy and in a way which covers the practical need.