Optical simulations for fire detectors

In this paper, we present the method for optical simulation that we have successfully applied to new designs of fire detectors, with a focus on optical scattering smoke detectors. Our simulation is based on a commercially available software tool for non-sequential ray-tracing and on measurements of the differential scattering cross-section of test fire aerosols. With optical simulation, we succeeded in predicting the main characteristics of an optical scattering smoke detector, the zero-smoke signal and the response signal to test fires with sufficient precision.     

Laboratory evaluation of smoke detectors for use in underground mines

Laboratory experiments were conducted to determine the responses of a prototype smoke detector and a commercially available photoelectric smoke detector to smoke particles generated from various combustion sources. The prototype smoke detector combines optical scattering measurements with ionization chamber measurements in order to reduce/eliminate nuisance alarms due to the presence of airborne dusts or diesel exhaust particles. The commercially available smoke detector is designed for use in harsh environments where airborne dust represents a major problem due to both nuisance alarms and detector contamination. In the experiments, the responses of the two detectors were measured when exposed to smoke particles from the exhaust of a diesel engine and from a variety of fire sources, including wood, coal, styrene butadiene rubber, and No. 2 diesel fuel. For the solid fuels, data were obtained for both smoldering and flaming combustions. This report describes the experiments, their results, and the use of these results as they apply to early-warning fire sensors capable of the rapid and reliable detection of fires in atmospheres that may or may not be contaminated by either airborne dust or the products produced from diesel engines.     

缩尺度试验火烟气特性实验研究

基于4种标准试验火开展缩尺度试验火烟气特性实验,研究试验火烟气特性在其尺度逐渐缩减过程中的变化规律,分析火灾烟气减光系数随时间的变化以及货架火灾探测器、吸气式感烟火灾探测器、点型感烟火灾探测器对各尺度试验火的报警响应特性。给出适用于高灵敏火灾探测器检测和评价的缩尺度试验火做法建议。     

Rapid Detection and Suppression of Mining Equipment Cab Fires

The National Institute for Occupational Safety and Health (NIOSH/PRL) conducted a series of large-scale experiments to evaluate the effectiveness of optical flame detectors, photoelectric smoke detectors, and combined ionization and photoelectric smoke detectors for rapidly detecting mining equipment cab fires. The detector alarm times were then used to trigger the discharge of a fire inerting system inside the cab to suppress cab material fires. This paper discusses the types of fire detectors tested, the experiments that were conducted, and the results that were obtained. Conclusions are that rapid detection of equipment cab fires can be achieved to trigger the discharge of a fire inerting system inside the cab to protect the operator in the cab.     

变电站电缆沟火灾探测试验与数值仿真研究

为探讨火灾探测器灵敏度对电缆沟火灾响应的影响程度,验证火灾监控系统的准确性,应用点式温度探测器、点式烟雾探测器、电缆式感温探测器和吸入式烟雾探测器4种火灾探测器,在标准变电站电缆沟防火分区内进行了全尺寸电缆火灾试验,测试不同灵敏度火灾探测器的火灾报警序列。根据电缆沟的实际尺寸,利用FDS搭建模拟明火和阴燃两种不同火灾场景,对不同灵敏度火灾探测器的温度场、有毒气体质量浓度和火灾报警顺序进行了分析和讨论。试验结果表明,在变电站电缆沟火探测中,电缆式感温探测器、吸入式烟雾探测器、点式感烟探测器火灾平均响应时间分别为41.2,111.4,331.8 s;吸入式感烟探测器的灵敏度对探测结果影响较大,其火灾报警响应时间比电缆型线性温度探测器约延迟50%。     

A Relative Time Analysis of the Performance of Residential Smoke Detection Technologies

A statistical study was conducted to compare the performance of different residential smoke detector technologies when exposed to different fire types. In order to facilitate comparisons between different fire and smoke growth rates, a non-dimensional smoke detector activation relative time was employed. Data from four major experimental studies was analyzed utilizing the relative time approach. The Common Language Effect Size, a measure of the probability that a particular detector technology will be the first to detect a fire of a particular type, was used to assess detector performance. The analysis confirmed previous results that ionization detectors, on average, respond faster to flaming fires, and that photoelectric detectors, on average, respond faster to smoldering fires. More importantly, this study also determined that the responses of ionization, photoelectric, and combination technologies are statistically equivalent for any given future residential fire That is, it cannot be determined with confidence which detector technology will alarm first to the next fire. Additionally, the analysis found that this statistical equivalence between detector technologies has not changed in the last 35 years despite increased fire growth rates associated with changes in furniture materials over that same time span.     

Determination of dynamic model parameters of smoke detectors

A simple model for the dynamic response of point-type smoke detectors is described. The model is based on two independent parameters: the characteristic length and the static response threshold. Experimentally determined values of the parameters for six commonly used point-type smoke detectors are reported. In the tests the free stream flow velocity was varied in the range of 0.2–0.8 m/s and the rate of rise of smoke density in the range of 0.1–2 dB/ms. The model parameters were determined from the experimental data by using the least squares fitting with regularisation. The characteristic length was found to vary in the range of 2–10 m indicating a smoke entry time constant in the range of 10–50 s at a flow rate of 0.2 m/s typical of smouldering fires. The response of photoelectric detectors was described by the model reasonably well. In the case of ionisation detectors, significant deviations were found. A method of using the model in fire safety engineering calculations is also presented.     

Influence of fire ignition locations on the actuation of smoke detectors and wet-type sprinklers in a furnished office

Experiments were conducted in a full-scale model office equipped with movable and fixed fire loads to explore the influence of ignition source (movable fire load(s)) conditions on smoke detector and sprinkler actuation. The interior plan dimension is 5.7 m × 4.7 m and the net ceiling height is 3.3 m. Both northeast and southeast wings have a 2.1 m × 0.9 m single door to be opened. Seven fire scenarios (seven different ignited fire load configurations) under natural ventilation were investigated experimentally. The results show that the amount of fire load at the initial stage in a room fire does not markedly affect smoke generation and does not significantly impact the actuation time of the smoke detectors. When the fire source is located near a corner, the plume corner effect greatly increases; smoke detectors and sprinklers can activate quickly and effectively actuate the fire suppression. When the fire source is located in the room's center, given the uncertainty regarding smoke detector and sprinkler actuation, it may not be possible to control the fire spread.     

Performance improvement of fire detectors by means of gas sensors and neural networks

Nowadays, fire detection systems are used world wide in order to protect life and goods. However, at the present time, detectors show poor features with regard to detection speed and reliability. They respond to only a few fire parameters like smoke particles and they do not take into account other important fire parameters such as gaseous products. In this paper, we present a new multi-sensor detector consisting of a commercial optical fire detector, a temperature sensor and selected semiconductor metal oxide gas sensors. The use of a multi-sensor detector requires a more sophisticated algorithm than the simple threshold rule. The new algorithms are typically based on pattern recognition systems, consisting of a pre-processing unit, a feature extraction unit and a classification unit. The choice of suitable methods for the feature extraction and the classification is difficult. Most often, the classifier depends on the type of the extracted features. In this paper two methods for the feature extraction with their suitable classifiers are presented and compared. However the classification is based on neural networks.The first algorithm consists of (i) a pre-processing unit; and (ii) a FFT-based feature extraction unit to resolve characteristic fire signatures. For that purpose a moving window has been introduced and a composed signal has been generated from the different pre-processed sensor responses. The algorithm also consists of (iii) a classification unit with a Learning Vector Quantization (LVQ) neural network to classify the extracted features to fire, not fire, or disturbing event.The second algorithm consists of a pre-processing unit and feature extraction method based on the scaling of the quadratic mean value. For this kind of feature extraction a back-propagation neural network as a classifier has been chosen.An important improvement towards the use of commercial detectors has been achieved using both of the above-described algorithms. The neural networks with suitable feature extraction methods were able to detect test fires more quickly than the commercial optical fire detector without generating false alarms by disturbing events.     

一种基于炭黑导电性能的感烟探测器的设想

在分析现有火灾探测器的探测原理、火灾发展过程及其产物的基础上，提出基于火灾产物炭黑粒子的一种感烟探测器的设想，为火灾探测器的研究提出了新的思路和方向。     

Monitoring Multiple Aspects of Fire Signatures for Discriminating Fire Detection

Numerous researchers are exploring multisensor detection as the principal means of discriminating between fire and nuisance sources. Multisensor detectors can monitor multiple aspects of a wide variety of signatures produced by flaming fires, non-flaming fires, and nuisance sources. This paper describes one program of small- and large-scale experiments that has been conducted using a prototype advanced fire detector with multiple gas sensors. An elementary analysis is applied to demonstrate that spacing guidance can be rationally developed for multiple gas sensors to detect fires of a particular threshold fire size, i.e., heat release rate. Discriminating between flaming fires, non-flaming fires, and nuisance sources could be achieved using either a threshold concentration or CO₂ rate-of-rise to identify flaming fires and a CO or CO₂ rate-of-rise for non-flaming fires. Time to detection was also compared to commercial smoke detectors, and the reductions in time were noted.     

Fire detection using smoke and gas sensors

Fire detection systems located in aircraft cargo compartments are currently based only on smoke detectors. They generate about 200 false alarms per year for US registered aircraft. The number of false alarms is growing as more planes are outfitted with smoke detectors and air travel expands. Moreover, the survivability of an aircraft in a fire scenario depends on the early detection of the fire. A fire detection system is developed based on the simultaneous measurements of carbon monoxide, carbon dioxide, and smoke. The combination of the rates of rise of smoke and either carbon monoxide or carbon dioxide concentration provides a potential fire alarm algorithm to increase the reliability of aircraft smoke detectors, and to reduce the time to alarm. The fire detection system with the alarm algorithm detected fires that were not alarmed by smoke sensors, and alarmed in shorter times than smoke sensors operating alone.     

Fire safety among the elderly in Western Australia

Unsafe dwelling environments may contribute to high morbidity and mortality of residential fire among the elderly people. This study investigated the prevalence of fire safety devices and related risk factors in elderly households. A series of convenience surveys was administered at 11 council community centres within metropolitan Perth, Western Australia, between August and October 2004. A total of 1188 older adults aged 65 years or over were recruited. The results found generally low prevalence for electric safety switches (56%), fire extinguishers (18%) and fire blankets (10%), while 72% had a functional smoke detector installed. Nearly a quarter of the participants had never thought of an escape route. Logistic regression analysis based on generalized estimating equations further showed that those living alone had a significantly lower prevalence of smoke detector and functional smoke detector, with adjusted odds ratios 0.48 (95% CI: 0.34–0.69) and 0.55 (95% CI: 0.41–0.75), respectively. Similarly, elderly people living in private rental housing appeared to be less equipped against residential fire relative to those in public rental and those occupying their own homes. As expected, elderly people with home contents insurance coverage had a significantly higher prevalence of fire safety devices. These findings have important implications for the government and policy makers if community fire safety for the elderly is to be improved.     

Risk factors for fatal residential fires

Residential fires are the most important cause of fire-related mortality in the United States. Previous research has concentrated on fatal fires in urban areas; considerably less is known about fatal fires in rural areas.We studied fatal and nonfatal residential fires in predominantly rural areas. Using a casecontrol design, we compared all 151 fatal fires (cases) in single-family dwellings in North Carolina during a 13-month period with a sample of nonfatal fires (controls). Case fires were identified through the medical-examiner system, and control fires that occurred within a few weeks of the case fires were chosen from the records of randomly selected fire departments statewide. For each fire, fire officials were interviewed about the dwelling, the fire, the people involved, and the fire-response system.Although heating incidents were the leading cause of fires, fatal fires were more likely to have been caused by smoking (31% of fatal fires vs. 6% of nonfatal fires). Mobile homes posed a higher risk of death if a fire occurred (odds ratio, 1.7; 95% confidence interval, 1.1 to 2.6), as did the absence of a smoke detector (odds ratio, 3.4; 95% confidence interval, 2.1 to 5.6). Smoke detectors were more protective against death in fires involving young children and when no one present was impaired by alcohol or drugs or had a physical or mental disability. The presence of an alcohol-impaired person was the strongest independent risk factor for death in the case of a fire (odds ratio, 7.5; 95% confidence interval, 4.4 to 12.7).In conclusion, residential fires are most likely to be caused by heating equipment or smoking materials. The risk of death is greatest in fires in mobile homes, in those involving alcoholimpaired persons, and in those in houses without smoke detectors. Reprinted with permission from The New England Journal of Medicine, 1992 Sep 17, 327 (12), pp. 859–863.     

Transport Time Lag Effect on Smoke Flow Characteristics in Long-Narrow Spaces

This paper focuses on the smoke transport lag time at the early stage of fires in long-narrow spaces, which is defined as the time from fire onset to the time when smoke reaches a given position on the ceiling. For a heat detector at a specific location on the ceiling, the smoke transport lag time is a part of the response time of the heat detector. Especially when the heat release rate is relatively small at the early stage of fires, the smoke transport lag time will be very long, which will hence lead to the increase of heat detector response time. It is clear that the prediction of smoke transport lag time is critical to the activation time of the heat detector. However, previous studies have much focused on fire characteristics in long-narrow spaces, leaving very few on the transport time lag. Therefore, in this study, a theoretical model regarding smoke transport time lag was developed for both steady and time-dependent fires based on the weak-plume theory. This model was validated by a series of reduced-scale experiments. It can be concluded from comparison that the predictions of this model agree reasonably well with the corresponding experimental results. Using the proposed method, the dimensionless equations of smoke transport time lag, velocity and temperature considering the smoke lag effect in a long-narrow space for time-squared fires were also theoretically deduced. Additionally, to further determine the applicability of ‘Quasi-steady’ state assumption for time-squared fires, a calculation method regarding the critical time was also developed. The outcomes from this study will be beneficial to the development of fire detection model in long-narrow spaces.     

Using multivariate statistical methods to detect fires

Fire detectors must accurately detect fires, but they should not respond to false alarms. Contemporary smoke detectors sometimes cannot discriminate between smoke and odor sources. These detectors can also be slow in responding to smoldering fire sources. In this paper, a statistical approach for detecting fires based on fusing sensor signals from multiple sensors is presented. The multivariate statistical approach, called principal component analysis, is used to compress the sensor information down to a small number of variables that can be interpreted more easily than the raw sensor signals themselves. Experimental results presented here show that the proposed approach is more accurate than a conventional smoke alarm, particularly for early detection of smoldering fires. However, this new approach does not overcome the problem of false alarms. In spite of this current limitation, the method discussed holds great promise for future fire detection applications.     

Combining Statistics and Case Studies to Identify and Understand Deficiencies in Fire Protection

Over the years, much information has been gathered about fires in fire investigation reports and statistics. This information may have been collected nationally by an agency or an insurance company, or locally by the local rescue service. The information thus gathered can be used to learn from these fires and thereby lead to improved fire safety in buildings. This paper describes a method for discovering technical deficiencies in the fire safety of buildings. The method offers a means of analysing several fires systematically with the aim of identifying factors characteristic of a problem in the system studied. In this paper, the method is illustrated through a study of severe fires in school buildings in Sweden. The aim is to discover the underlying factors that cause some fires to grow and become severe. The method is considered a useful tool for discovering the underlying factors to or causes of fires.     

几种火灾探测器在公路隧道中的应用

如何迅速探测公路长隧道的火灾,一直是国内外研究的课题。隧道火灾报警是隧道安全系统非常重要的一部分。隧道火灾探测器的种类很多,本文根据隧道几种常见火灾探测器的工作原理、结构、性能特点及优缺点,简述其在高速公路隧道上的应用,并为公路隧道火灾探测器的选择提供参考。     

Fire-induced pressure and smoke spreading in mechanically ventilated buildings with air-tight envelopes

Fire-induced pressures have not been considered dangerous in building fires, but the situation may be changing as building envelopes become increasingly air-tight. In this study, we investigate whether this can change the fire development and pose new risks for structural and evacuation safety. We used experiments to validate the numerical models, and models for simulating the fire development in buildings with different air-tightness levels. The simulations considered air permeability values typical for traditional, modern and Near-Zero buildings. Three different smoke damper configurations were studied, and the fire growth rates were varied from medium to ultra-fast. The results showed that transitioning from traditional and modern buildings to Near-Zero buildings can sufficiently increase the peak overpressures from fast-growing fires to cause structural damage. Conditions were identified for avoiding excessively high overpressures, while preventing smoke from spreading through the ventilation system.     

Advanced fire detection using multi-signature alarm algorithms

The objective of this work was to assess the feasibility of reducing false alarms while increasing sensitivity through the use of combined conventional smoke detectors with carbon monoxide (CO) sensors. This was accomplished through an experimental program using both real (fire) and nuisance alarm sources. A broad selection of sources was used ranging from smoldering wood and flaming fabric to cooking fumes. Individual sensor outputs and various signal-conditioning schemes involving multiple sensors were explored.The results show that improved fire-detection capabilities can be achieved over standard smoke detectors by combining smoke measurements with CO measurements in specific algorithms. False alarms can be reduced while increasing sensitivity (i.e., decreasing the detection time for real fires). Patented alarm criteria were established using algorithms consisting of the product of smoke obscuration and the change in CO concentration. Alarm algorithms utilizing ionization detector smoke measurements proved to be more effective than measurements from photoelectric detectors.