Locating the very early smoke detector apparatus (VESDA) in vertical laminar clean rooms according to the trajectories of smoke particles

Proper locating of a very early smoke detector apparatus (VESDA) in cleanrooms is an important issue for fire safety. The main aim of this study is to analyse the proper locations of a VESDA by determining the trajectories of smoke particles in the early stages from a fire in a vertical laminar flow clean room using computation fluid dynamics (CFD). The CFD model was first verified by experimental data of a reduced-scale clean room. Several influential factors on the trajectories of smoke particles including particle size, fire source temperature and fire location were then studied for a full-scale clean room. Results show that the fire source is the most notable factor influencing the trajectories of smoke particles. When the fire source was located at the centre of the room, the smoke particles travelled to the centre of the return air plenum (RAP). If the fire started close to the return air shaft (RAS), the smoke particles reached the RAP close to the top. If the fire started far away from the RAS, the smoke particles arrived at the RAP close to the bottom.     

Characterization of Radon Decay Products in a Domestic Environment

Field measurements of the concentration and activity size distribution of radon decay products were conducted in a one-story house located in the Princeton, NJ area. Radon concentration and particle number concentration were also measured. The concentration and activity-weighted size distribution of radon decay products were determined using a microcomputer-controlled, semi-continuous screen diffusion battery system with 6 parallel sampler/detector units. A condensation nuclei counter was used for the measurements of indoor panicle number concentration. Several measurements were made in the living room as well as more than one hundred measurements in the master bedroom of the Princeton house. Aerosols were generated from taking a shower, burning a candle, smoldering a cigarette, vacuuming, and cooking. Therefore, the influence of various indoor panicle sources on the behavior of radon decay products was investigated. With panicles generated from typical household activities, Potential Alpha Energy Concentration (PAEC) increases and the unattached fraction decreases. Larger panicles generated from cigarette smoke and cooking dramatically shifted most of the radon decay products into the attached mode (15-500 nm). With regard to the higher attachment rate, the size distributions of radon decay products remained stable for long periods of time after particle generation. On the other hand, aerosols produced from candle burning and vacuuming were much smaller, with an average attachment diameter of 15 nm. These panicles did decrease the unattached fraction, especially during the aerosol generation period. However, the size distributions of radon decay products returned to the background condition within ISO minutes after the end of particle generation. In these cases, the panicles had a higher deposition rate and a lower attachment rate. The dose of alpha radiation per unit radon concentration resulting from each of these aerosol conditions was calculated using the measured activity size distributions and the most recent James dosimetric model. These doses to basal cells at a breathing rate of 0.45 m³ hr¹ ranged from 3 to 14 μGy Bq^?1 hr while the dose to secretory cells at a breathing rate of 1.5 m³ hr¹ ranged from 13 to 77 μGy Bq^?1 hr for the various aerosol conditions.     

电缆火灾烟雾生成特性及声波团聚消烟的实验研究

由于城市建设的需要,越来越多的城市采用地下电缆隧道输送电力,隧道火灾事故严重威胁城市安全与电力输送。电缆火灾生成的烟雾是妨碍消防人员施救过程的重要因素,现有的烟雾控制方法主要从隧道的通风角度出发,考虑如何快速将烟雾排出隧道,主要包括自然排烟与机械排烟2大类,均存在一定的局限性。声波团聚技术是一种利用高强声场快速消除气溶胶的处理技术,已有文献表明该技术可有效消除聚苯乙烯燃烧烟雾。本文进行了声波团聚技术消除电力隧道火灾烟雾的实验研究。采用TSI 3330光学粒度仪测量火灾烟雾颗粒粒径,结果表明,VV电缆烟雾的粒径主要分布在1μm附近,而YJV电缆烟雾除了1μm左右的细颗粒外,还包含了较多0.3μm的亚微米颗粒。测试水平敷设、垂直敷设条件下电缆火灾烟雾的产烟特性,电缆外护套层、填充层及绝缘层的产烟特性,电缆持续受热、受热20 s和受热50 s情况下的产烟特性,并通过测量透射光强度计算其烟雾透光率、能见度、产烟速率等参数。结果表明,电缆材料对其燃烧产烟影响较大,VV电缆产烟量较大,燃烧约60 s后其透光率便降至0.2附近,而YJV电缆的产烟量少于VV电缆;水平燃烧时,其整体烟雾透光率低于垂直燃烧;电缆外护套层材料燃烧后产烟量最多,约60 s时透光率降至0附近,团聚室内充满了大量白色烟雾。设计并搭建了声波团聚消除电力隧道烟雾的实验平台,由信号发生器产生正弦信号,经功率放大器放大后,通过驱动压缩式驱动器发出高强声波,分析有、无声波作用下电缆火灾烟雾的透光率变化。实验表明,声波团聚能够迅速提升电缆火灾烟雾的能见度,当声功率为12 W、频率为1.5 kHz时,仅需0.2 min便可使团聚室的透光率提升至0.6,达到人员逃生阈值。声波消烟过程中,声频率是关键参数。电缆火灾烟雾的团聚效果对声波频率十分敏感,最佳频率为1.5 kHz,偏离最佳频率越多,声波团聚的效果越差;声功率对消烟效果影响较大,声功率越大,消烟效果越佳,当声功率达到一定程度时,团聚效率提升速率减缓。     

Experimental studies on time-dependent size distributions of smoke particles of standard test fires

The time-dependent size distributions of smoke particles are measured by SMPS spectrometer as experiments go on, respectively, for four standard fires, i.e. TF2, TF3, TF4 and TF5. The results suggest that, for the TF4, the normalized number distributions of smoke aerosol be best fitted with lognormal functions and little time-dependency be shown throughout the experiments. It is also indicated that the best fitting curves of the normalized number distributions of smoke particles change from the so-called under-lognormal fittings to over-lognormal fittings for the TF2, TF3 and TF5, as time moves. In addition, a common changing trend of the size distribution curves can be drawn for the three standard fires. Namely, the curves mainly drift toward larger diameters of smoke particles and the peaks of the curves keep increasing as time goes by for each standard test fire.     

火灾探测过程模拟研究

将火灾模型和烟气传感器结合起来模拟传感器对不同火灾情况的反应。将NIST的FDS模型和Duisburg-Essen大学通讯系统学院开发的烟气传感器模型结合了起来。某火灾烟气流动的模拟结果作为适合烟气传感器模型的输入数据。为了模拟烟气传感器，选择了几个必要的参数来描述烟气、传感器和房间的情况。烟气粒径的大小分布是描述烟气的一个重要参数。对影响粒径大小分布的烟气颗粒的凝结做了适当处理。联合模型的模拟结果与开敞式火灾和阴燃火灾的测量值做了比较。模拟了一个散射光感器和一个电离室。测量和模拟结果显示，传感器模拟的重质取决于所燃烧的燃料。     

Analysis of indoor particle size distributions in an occupied townhouse using positive matrix factorization

From late 1999 to early March 2000, measurements of particle number (particles 0.01-20 microm in aerodynamic diameter) concentrations were made inside of a townhouse occupied by two non-smoking adults and located in Reston, VA (approximately 25 miles northwest of Washington, DC). The particle size measurements were made using an SMPS and an APS as well as a Climet optical scattering instrument. In this study, positive matrix factorization (PMF) was used to study the indoor particle size distributions. The size distributions or profiles obtained were identified by relating the obtained source contributions to the source information provided by the occupants. Nine particle sources were identified, including two sources associated with gas burner use: boiling water and frying tortillas. Boiling water for tea or coffee was found to be associated only with the smallest particles, with a number mode close to the detection limit of the SMPS (i.e., 0.01 microm). Frying tortillas produced particles with a number mode at about 0.09 microm while broiling fish produced particles with a number mode at about 0.05 microm. A citronella candle was often burned during the study period, and this practice was found to produce a 0.2-microm modal number distribution. Other indoor particle sources identified included sweeping/vacuuming (volume mode at 2 microm); use of the electric toaster oven (number mode at 0.03 microm); and pouring of kitty litter (volume mode over 10 microm). Two outdoor sources were also resolved: traffic (number mode at about 0.15 microm) and wood smoke (major number mode at about 0.07 microm). The volume distributions showed presence of coarse particles in most of the resolved indoor sources probably caused by personal cloud emissions as the residents performed the various indoor activities. PRACTICAL IMPLICATIONS: This study has shown that continuous measurements of indoor particle number and volume concentrations together with records of personal activities are useful for indoor source apportionment models. Each of the particle sources identified in this study produces distinct size distributions that may be useful in studying the mortality and morbidity effects of airborne particulate matter because they will have different penetrability and deposition patterns.     

飞机货舱典型可燃物燃烧火灾特征参数试验研究

摘 要：光电式火灾烟雾探测器是目前民用飞机货舱使用的主流火灾探测器,是保障飞机安全运行的关键,该探测器是基于烟雾颗粒对光的散射信号来进行报警的,但是由于空气中悬浮颗粒物（水蒸气或灰尘等）也具有散射效应,同样会触发火灾探测器发生报警,这种原理上的缺陷造成的误报情况时有发生。通过对飞机货舱典型燃烧物瓦楞纸片、榉木和棉绳的蓝光散射功率（表征为表面积浓度）、红外光散射功率（表征为体积浓度）和颗粒物索特平均粒径火灾特征参数进行分析,为复合探测器的研发优化火灾特征参数。结果表明：在常压条件下,蓝光和红外光对颗粒物浓度的变化有很好的响应,索特平均粒径可以区分火灾烟雾颗粒和非火灾烟雾颗粒,可以有效降低误报率。     

Prediction of heat and smoke movement in enclosure fires

In order to understand the response of a detector to a given fire in an enclosure, it is necessary to relate the local thermal and aerosol characteristics actually sensed by the detector to the physical and geometrical properties of the fire and the enclosure. This paper presents computations designed to predict the evolution of the size distribution of smoke aerosol as it ages, as well as the large-scale air movement and temperature fields generated by an enclosure fire.

The computations contain three main ingredients: first, a finite difference solution for the air movement and temperature generated by a prescribed source of heat used to represent a fire in a closed form; second, the computer evaluation of an exact solution to the ageing equation correspond to the evolution of an experimentally observed size distribution; and third, a particle tracking scheme which permits the smoke aerosol to be followed in space and time as it gradually fills the room. No nonphysical empirical parameters (e.g. turbulence models) are employed in these calculations. The mathematical and physical models are summarized briefly, but most emphasis is placed on displaying results. Sample calculations are presented, comparisons are made with relevent experiments, and predictions of the local environment experienced by a detector due to the occurrence of an enclosure fire are shown.     

Experimental Investigation of Acoustic Agglomeration and Sonic Soot Deposition on Smoke Alarms Incorporating Emerging Sounding Technologies

Traditional residential smoke alarms producing a high-frequency T-3 sound have been shown to exhibit sonic deposition of acoustically-agglomerated soot when they sound in the presence of smoke produced in a typical residential fire. The intense acoustic field generated by alarm sounders, which produce these traditional smoke alarm tones, causes colliding soot particles to adhere to one another and eventually settle onto surfaces as their mass increases. The sonic field generated by the horn creates a pulsed flow around the alarm openings that can lead to increased soot deposition in this area. The agglomerated particles then can deposit on the smoke alarm proximate to the horn. The presence of the acoustically-agglomerated soot deposition on alarms has become an accepted forensic technique used to determine if an alarm sounded in the presence of soot. In recent years, new sounding technologies have been introduced for smoke alarms in order to improve their effectiveness in alerting people to fire emergencies who may not respond reliably to traditional smoke alarm tones and patterns. Many researchers have studied the effectiveness of different alarm signals and have found that low-frequency tones and voice messages show increased effectiveness in alerting people, particularly at-risk individuals such as children and the hearing impaired. The new alarms producing low-frequency tones and voice messages generate a far different acoustic field than traditional smoke alarms and require additional understanding of the acoustic agglomeration and sonic soot deposition patterns. A low-frequency alarm sounder, a voice-incorporated alarm using one sounder to generate both the smoke alarm pattern and a voice message, and a voice-incorporated alarm using two sounders to generate the smoke alarm pattern and voice message separately were exposed while sounding to five different smoke sources representative of residential fires. When examined for the presence of enhanced soot deposition, the new alarm sounders solely producing a voice message did not exhibit sonic soot deposition but sounders that produced both the traditional smoke alarm pattern and voice message did exhibit sonic soot deposition. This indicates that the deposition is due to the traditional T-3 alarm sound rather than the voice message. Additionally, low-frequency sounders exhibited sonic soot deposition but only in the presence of the heavy, resin-like tarry deposition from the smoldering polyurethane foam source. As has been found in other studies, this study confirms that the presence of enhanced soot deposition or tarry residue deposition proximate to the horn of a smoke alarm is a reliable indicator that the alarm sounded in the presence of deposition. However, the absence of enhanced soot deposition proximate to the horn of the alarm is not necessarily a reliable indicator that the alarm did not sound in the presence of soot.

     

Investigation of smoke particulates generated during the thermal degradation of natural and synthetic materials

This paper describes results obtained in a program investigating the physical and chemical properties of particulates generated during the burning of three commonly used materials. Small samples of wood, rigid urethane foam and polyvinyl chloride plastic have been burned under non-flaming conditions at room temperature in a ventilated combustion products test chamber. Continuous measurements have been made of smoke particle average size, particle size distributions, particulate optical density, particulate volume and mass concentrations, and particulate index of refraction utilizing an aerosol sampling system and an in situ scattered and attenuated light optical system. Non-flaming tests have been run in different ventilation gas compositions and at three radiant heating levels in an attempt to simulate real-fire situations. A review of previous results obtained by the aerosol sampling system is followed by presentation of new data taken with the in situ optical system. This data shows that average smoke particle sizes tend to vary during a test. Furthermore, particle sizes are generally larger for tests run at the highest heating rates. Available data also indicates that the physical characteristics of the smoke particles are relatively for non-flaming conditions. These results are consistent with previously reported aerosol sampling data. Also, continuous optical density measurements are presented, which allow the determination of the relative tendency of a smoldering material to obscure vision under different conditions. Finally, scanning electron microscope photographs provide new information on the detailed nature of smoke particles generated during non-flaming combustion.     

Carcinogen specific dosimetry model for passive smokers of various ages

Studies indicate that being exposed to second hand smoke increases the chance of developing lung cancer. Understanding the deposition of carcinogenic particles present in second hand smoke is necessary to understand the development of specific histologic type cancers. In this study, a deposition model is presented for subjects of various ages exposed to sidestream smoke. The model included particle dynamics of coagulation, hygroscopic growth, charge and cloud behavior. Concentrations were varied from the maximum measured indoor concentrations (10(6) particles/cm3) to what would be expected from wisps of smoke (10(8) particles/cm3). Model results agreed well with experimental data taken from human subject deposition measurements (four studies). The model results were used to determine the dose intensity (dose per unit airway surface area) of Benzo[a]pyrene (BaP) in the respiratory tract for subjects of various ages. Model predictions for BaP surface concentration on the airway walls paralleled incident rates of tumors by location in the upper tracheobronchial region. Mass deposition efficiency was found to be larger for younger subjects, consistent with diffusion being the predominant mechanism for this particle size range. However, the actual dose intensity of BaP was found to be smaller for children than adults. This occurred due to the predominant effect of the smaller initial inhaled mass for children resulting from smaller tidal volumes. The resulting model is a useful tool to predict carcinogen specific particle deposition.     

Generation and Transport of Smoke Components

Smoke is a mixture of gases, vapors, and suspended particulate matter, or aerosols. The nature of the aerosol component of smoke can play a significant role in its deposition in the fire environment and in its lethal and sublethal effects on people. This paper presents the current state of knowledge about smoke aerosol phenomena that affects smoke toxicity: soot generation, fractal structure of soot, agglomerate transport via thermophoresis, sedimentation, and diffusion, agglomerate growth through coagulation and condensation, and the potential for the aerosols to transport adsorbed or absorbed toxic gases or vapors into the lungs. Tables are included for measured smoke yields and aerodynamic particle sizes, equations and references are provided for the smoke agglomerate transport properties and wall loss, and key literature references are provided for adsorption of irritant gases on soot particles and water droplets and the toxicity of nanosize particles.     

Oxidation characteristics of airborne carbon nanoparticles by NO(2)

The oxidation characteristics of airborne carbon nanoparticles were investigated at various temperatures and NO(2) concentrations. Airborne carbon nanoparticles were generated by spark-discharging method using nitrogen as a carrier gas. Monodisperse carbon particles classified using a differential mobility analyzer were introduced into a tube furnace with NO(2) for oxidation reaction. The size distributions of oxidized carbon aerosol particles were measured using a scanning mobility particle spectrometer system which consisted of a differential mobility analyzer and a condensation particle counter. The result was that as NO(2) concentrations and reaction temperatures increased, the surface oxidation rate of carbon aerosol particles increased. For NO(2) gas, the activation energy of the oxidation reaction was approximately 76.3 kJ/mol. The activation energy of the oxidation reaction for the mixture of NO(2) and O(2) gases was 65.9 kJ/mol, which is smaller than that for only NO(2) gas.     

Wall Smoke Deposition from a Hot Smoke Layer

Smoke deposition from a hot smoke layer onto wall surfaces was studied in a hood apparatus using polymethylmethacrylate, polypropylene, and gasoline as fuels. Based upon prior analysis by Butler and Mulholland, the smoke deposition was expected to be dominated by thermophoresis. The deposited smoke samples were collected on glass filter paper attached to the hood wall and the mass per unit area of smoke deposited was measured gravimetrically. Measurements were made of quantities required for the prediction of thermophoretic smoke deposition. The smoke deposition measured in the experimental program was well predicted by the thermophoretic smoke deposition equation. The thermophoretic smoke deposition equation was found to be suitable for predicting smoke deposition onto wall surfaces exposed to fire environments.     

Verification of ionization chamber theory

The response of a standard ionization detector to artificially generated test aerosols as well as to test fire and smoke has been determined experimentally. The size distribution and number concentration of these aerosols have been measured by independent methods.     

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.     

Characterizing Firebrand Exposure from Wildland–Urban Interface (WUI) Fires: Results from the 2007 Angora Fire

This study examines the size distribution and other characteristics of firebrand exposure during the 2007 Angora fire, a severe wildland–urban interface fire in California. Of the 401 houses that received direct interface fire exposure 61% were destroyed and 30% did not burn at all. The ignition of buildings by wind-driven firebrand showers and the starting of “spot fires” in unburned vegetation ahead of wildfires have been observed for some time. Empirically quantifying the exposure severity or describing how many firebrands of what size and over what duration and distance cause ignition problems of concern has not yet been possible. However, a unique opportunity to gather empirical firebrand data from an actual interface fire evolved in the days immediately following the Angora fire. Digital analyses of burn patterns from materials exposed to the Angora fire were conducted to determine firebrand size distributions. It is probable that some burn patterns were larger in area than the firebrands due to progressive combustion or melting, but it was assumed that the overall size distributions of burn pattern areas were representative of actual firebrand sizes. This assumption was investigated by exposing sections of materials collected in the Angora fire to wind driven firebrands generated in the laboratory using the unique NIST Dragon’s lofting and ignition research facility (NIST Dragon’s LAIR facility). The firebrand size distributions reported were compared to firebrand size distributions from experimental firebrand generation in both recent laboratory building ignition studies conducted by NIST and from historical firebrand field studies. Such data is needed to form the basis of effective and appropriate interface fire hazard mitigation measures as well as modeling fire spread. Comparisons are made to current wildfire protection building construction regulations and test standards. The most salient result of this study is documentation of the consistently small size of firebrands and the close correlation of these results with the sizes of experimentally generated firebrands.     

Numerical simulation of the penetration capability of sprinkler sprays

Computational models have been utilized to investigate the penetration capability of sprinkler sprays directly above a fire source with respect to water flow rate, spray drop size, and spray momentum. The spray models are generated by assigning a representative drop size, mass flow rate, discharge speed, and discharge angle for each of 275 trajectories in such a way that they produce computed results which match the measured water flux distribution and spray momentum in the absence of a fire. The spray/fire plume interaction models are created by combining the spray models using a Lagrangian particle tracking scheme with free-burn fire plume models. Actual delivered densities and penetration ratios are computed through the interaction simulations at six flow rates, three fire sizes, and two ceiling heights. Drop sizes and spray momentum at two flow rates are increased by 25 and 50% from the original values without changing the other spray characteristics in order to investigate the effects of each parameter on penetration capability independently. The study indicates that there is an optimal flow rate for a given sprinkler that gives the highest penetration ratio within a practical flow range. It is also shown that increasing drop size is a much more effective way for obtaining a higher penetration ratio compared to increasing spray momentum.     

Size resolved ultrafine particles emission model--a continues size distribution approach

A new parameterization for size resolved ultrafine particles (UFP) traffic emissions is proposed based on the results of PARTICULATES project (Samaras et al., 2005). It includes the emission factors from the Emission Inventory Guidebook (2006) (total number of particles, #/km/veh), the shape of the corresponding particle size distribution given in PARTICULATES and data for the traffic activity. The output of the model UFPEM (UltraFine Particle Emission Model) is a sum of continuous distributions of ultrafine particles emissions per vehicle type (passenger cars and heavy duty vehicles), fuel (petrol and diesel) and average speed representative for urban, rural and highway driving.The results from the parameterization are compared with measured total number of ultrafine particles and size distributions in a tunnel in Antwerp (Belgium). The measured UFP concentration over the entire campaign shows a close relation to the traffic activity. The modelled concentration is found to be lower than the measured in the campaign. The average emission factor from the measurement is 4.29E + 14 #/km/veh whereas the calculated is around 30% lower. A comparison of emission factors with literature is done as well and in overall a good agreement is found.For the size distributions it is found that the measured distributions consist of three modes — Nucleation, Aitken and accumulation and most of the ultrafine particles belong to the Nucleation and the Aitken modes. The modelled Aitken mode (peak around 0.04-0.05 μm) is found in a good agreement both as amplitude of the peak and the number of particles whereas the modelled Nucleation mode is shifted to smaller diameters and the peak is much lower that the observed.Time scale analysis shows that at 300 m in the tunnel coagulation and deposition are slow and therefore neglected.The UFPEM emission model can be used as a source term in dispersion models.     

Evaluating the flammability of wood-based panels and gypsum particleboard using a cone calorimeter

This study examined the combustion characteristics of wood-based panels and gypsum particle board (GPB) made from wood particles using a cone calorimeter according to the ISO 5660-1 specifications. The combustion characteristics of the wood-based panels and GPB were measured in terms of the time to ignition (TTI), heat release rate (HRR), smoke production rate (SPR) and CO yield under a fire condition. The results demonstrated variations in the burning characteristics between the wood-based panels and a significant influence of the surface materials and construction elements on the HRR and SPR. The HRR, SPR and the CO yield of GPB were significantly lower than those of the wood-based panels.