Measuring modified glass bulb sprinkler thermal response in plunge and compartment fire experiments

Automatic fire sprinklers use a heat sensitive element such as a glass bulb or fusible link to respond to the heat from a fire. The response of commercial fire sprinkler glass bulbs has been extensively characterised in convection-dominated dry gas flows but in real fires there may be more factors that influence the heat transfer to the bulbs such as radiation from the fire or cooling from adjacent sprinkler sprays. The time of activation is the only indication of the thermal response of typical commercial fire sprinklers using glass bulbs to a fire, but direct temperature measurement using a modified proxy may provide a better understanding of how sprinklers respond in a complex environment. Modified glass bulbs have been created that allow a thermocouple to be inserted in the bulb for direct temperature measurement. In this paper, the thermal response of sprinklers with these modified bulbs has been observed in hot-air wind tunnel plunge experiments and full scale room fire experiments. At the time of activation the measured temperature of the modified sprinklers was found to be higher than the nominal activation temperature specification for the unmodified sprinklers. For the compartment fires, a thermal response model generally predicted longer sprinkler activation times based on ceiling jet temperature and velocity measurements than was observed experimentally.     

The Response Time of Different Sprinkler Glass Bulbs in a Residential Room Fire Scenario

The response time of fire sprinklers is essential for their performance, especially in applications where life safety protection is desired. The earlier the sprinkler activates, the smaller the size of the fire. Most commercial residential sprinklers are fitted with 3 mm, 68°C glass bulbs. However, thinner sprinkler glass bulbs with lower operating temperatures are available. The aim of this study was to determine the response time—and the corresponding heat release rate—of different glass bulbs in a residential room fire scenario. A series of tests were conducted inside a compartment measuring 3.66 m by 3.66 m having a ceiling height of 2.5 m. The compartment was either enclosed or had two walls removed to provide a more ventilated scenario. A propane gas burner was positioned at one of the corners. The mass flow rate of the gas was controlled such that either ‘slow’, ‘medium’ or ‘fast’ fire growth rate scenarios were simulated. In each test, nine Response Time Index (RTI) and operating temperature combinations were tested. Each test was replicated three times. In addition, two commercial fire detectors were tested. The results show that the fire is considerably smaller upon activation with a combination of a low RTI and a low operating temperature, as compared to the 3 mm, 68°C glass bulb typically used for residential sprinklers. The operating temperature proved to have a larger impact on the results than the RTI. The heat from the fire was typically detected by the fire detectors prior to the activation of the sprinkler glass bulbs, especially for the ‘slow’ and ‘medium’ fire growth rate scenarios.     

Influence of fire source locations on the actuation of wet-type sprinklers in an office fire

An experiment is conducted on a full-scale model office and an actual sprinkler system to explore the influence of fire source locations on sprinkler actuation. The office space is a brick structure that measures 5.7 m in interior length, 4.7 m in width and 2.4 m in ceiling height, and equipped with a sprinkler system. The investigated fire source (100 kW LPG burner) locations include the room center, wall centers, room corner, and other locations at different distances from sprinklers. The results show that actuation of the sprinklers is affected by the fire source locations and the heat conduction properties of the glass temperature-sensing bulb. Average actuation time of all the tests is 102 s, around 40 s faster than if the fire source is located in the room center. For fire sources in corners, sprinklers are quickly activated at the experimental time 75 s, showing concentrated hot gas flow.     

Numerical simulation of the wind shadow effect on the convective heat transfer to glass bulb sprinklers

A theoretical analysis of the wind shadow effect caused by the arms of the sprinkler frame has been performed using a finite volume computer code. The calculations show that the influence of the arms of the frame upon the convective heat transfer to the bulb is small when the arms of the sprinkler frame and the bulb are orientated perpendicular to the flow. The arms of the frame cause a slight acceleration of the flow around the bulb. Hence, the heat transfer to the bulb in this orientation is somewhat greater than for free flow around a cylinder. In the case when the arms of the sprinkler frame are aligned with the flow, the heat transfer is decreased by approximately a factor of two for the particular geometry considered. This is in agreement with results from wind-tunnel tests for the same geometry. The Nusselt number for this case is still roughly proportional to the square root of the Reynolds number. This finding is of practical importance, as the lumped mass theory for calculating the time to operation of sprinklers relies heavily on the assumption of a square root dependence of the Reynolds number. Good agreement is found between calculated and measured velocity profiles in the region between the glass bulb and the upstream arm of the frame, when the arms are aligned with the airflow.     

Model scale tunnel fire tests with automatic sprinkler

The study focuses on the performance of an automatic sprinkler system in a model scale tunnel with longitudinal ventilation. A total of 28 tests were carried out in a 1:15 model scale tunnel using an automatic sprinkler system with glass bulbs. The maximum heat release rate, energy content and failure of the automatic sprinkler system were analysed. The results show that high ventilation rates and low water flow rates result in a failure of the automatic sprinkler system in a longitudinal ventilated tunnel fire. The main reason for the failure under the tested water flow rates was the effect of the longitudinal flow on the fire development and the hot gas flow close to the sprinklers. The fire development and the activation heat release rate of the first activated bulb are intimately related to the ventilation velocity. The fire spread to the neighbouring wood crib was investigated and a presentation of tests conducted using a deluge system are given.     

Fire tests to evaluate CPVC pipe sprinkler systems without fire resistance barriers

Nine full-scale fire tests were conducted to assess the adequacy of exposed chlorinated poly vinyl chloride (CPVC) pipe and fitting sprinkler systems installed in light hazard occupancies. The tests were conducted in an enclosure using six different types of automatic sprinklers including QREC pendent and sidewall sprinklers, a pendent residential sprinkler, and a sidewall residential sprinkler. Two types of fires, fast growing and slow growing, were used as test fires.The sprinkler in each test was operated with the normal operation pressure until the test fire was almost completely suppressed. Next, to assess the integrity of piping systems after fire exposure, the water pressure was increased to 12.1 bar and maintained for 10 min and then were visually inspected for any leakage while hydrostatic pressure was maintained at 12.1 bar. No leakage was detected in any of the tests.The results of the tests indicate that sprinkler systems based on exposed CPVC pipe and fittings can be safely installed in light hazard occupancies and will provide adequate protection when installed to all the relevant standards.     

CMSA喷头动态热性能研究

采用风洞试验方法研究下垂型和直立型CMSA喷头的动态热性能,分析总结CMSA喷头的导热系数和响应时间指数的特点。导热系数由等速率升温试验计算。可以考虑采用ESFR喷头的计算公式计算CMSA喷头的导热系数和响应时间指数,采用普通洒水喷头的分类将其归入标准响应喷头的范围。     

智慧型自动喷水灭火系统软件的研发

针对传统自动喷水灭火系统存在火灾响应时间长、只能被动启动等缺点,以及为适应消防物联网发展的需要,基于大数据、云计算及物联网技术,提出了智慧型自动喷水灭火系统软件的研发方案。将传统被动型喷水灭火系统,升级为主动启动型自动喷水灭火系统,实现喷头状态远程监控、精准定位,组群喷头启动、早期灭火。系统无需人员24 h 值班,管理人员通过手机、电脑、平板电脑等终端设备对系统进行日常监控和早期火灾的喷水灭火。通过全尺寸火灾试验验证系统的联动应用性能和相关技术参数,对系统的工程应用提供了参考。     

Temperature and velocity correlations in room fires for estimating sprinkler actuation times

Automatic sprinklers are increasingly used in residential occupancies to provide active fire protection. These sprinklers, known as quick response and residential sprinklers, may be located either at the ceiling (pendent-style) or on a wall (sidewall-style). Though several fire models are available for estimating actuation times for sprinklers located under unobstructed ceilings, these use engineering correlations that do not apply to residential-sized rooms. Thus, data are needed for estimating sprinkler actuation times for residential occupancies.This paper reports on fire tests that were conducted in various sized rooms to obtain temperature and velocity data for 73 kW, 100 kW, and 147 kW fires. The data were then used to develop nondimensional correlations for temperature and velocity at the sprinkler locations. The temperature data revealed a significant temperature transient in the hot gas layer, and thus a nondimensional correlation describing the transient phenomenon was developed. These correlations compared reasonably well with experimental data, and they were used to estimate the sprinkler actuation times. The estimates were in reasonable agreement for the pendent sprinkler, except for the smallest fire in a 4.27 m by 4.27 m occupancy. The estimates for sidewall sprinkler acuation were significantly lower than experimental values. This may have been due to the sprinklers' heat losses, which were not accounted for in the calculation.     

Development of a computational model simulating the interaction between a fire plume and a sprinkler spray

Numerical simulations to predict actual delivered densities (ADDs) of early suppression fast response (ESFR) sprinklers in heptane spray fire scenarios were sought. First, in order to supply input data for the development of numerical models and experimental data for validation of the models, four sets of measurements were carried out: the momentum and water flux distribution of two ESFR sprinkler sprays without fire; the temperature and axial velocities along the axis of free-burn fires; and the actual delivered densities. Then, a numerical model for a sprinkler spray was completed by assigning the representative drop size, mass flow rate, discharge speed and discharge angle of 275 trajectories in such a way that they produced reasonable agreement with the measured water flux distribution and spray momentum in the absence of fire. A numerical model for the free-burn fire was created by assigning a heat flux distribution on a horizontal surface and simulating a central, vertical air jet used in the experiment, varying parameters until a reasonable match was established with the measured temperatures and the axial velocities along the axis. Numerical computations of actual delivered densities were carried out by combining the water spray model and the free-burn fire model for different water flow rates of the sprinklers. The ADDs obtained from the simulations compared reasonably well with those from the measurements.     

Full-scale fire tests and the development of design criteria for sprinkler protection of mobile shelving units

In early 1991, a new sprinkler system was planned for the existing National Archives/National Library of Canada building in Ottawa. A major challenge in the design and installation of the sprinkler systems was to protect mobile compact shelving units located in the three levels below grade. Storage of documents in these shelving units is typically within 178 mm of the concrete slab ceiling. The minimum clearance permitted by the sprinkler system installation standard is 457 mm from the sprinkler deflector to the top of the storage. To conform with the sprinkler design standard, the top level or levels of storage would have had to be removed and additional storage space acquired. Because of the annual cost of this additional storage, an investigation was begun to determine feasible alternatives that would permit a reduction in clearances between sprinklers and storage, while maintaining an acceptable level of fire safety. This paper describes the series of five full-scale fire tests that were conducted to assess various fire protection options. Based on these tests, design criteria were developed for a sprinkler system using quick response horizontal sidewall sprinklers to protect the mobile shelving units. An overview of this technically based fire protection system for use in protecting shelving units with reduced clearance is also presented.     

水喷淋保护下防火玻璃作为防火分隔物的试验研究

针对我国大空间建筑日益增多，而防火分隔手段相对匮乏，不能满足建筑防火设计需求的现状，通过实验证明了在水喷淋作用下高强度单片铯钾防火玻璃作为防火分隔的安全性，通过实验提出在实际运用中具体的使用参数（包括喷头选型、单位面积上水流量、压力、喷头的具体参数），该实验为高强度单片铯钾防火玻璃作为防火分割物应用于大空间建筑提供了有益的实验支持。     

特殊应用喷头喷水强度均匀性试验研究

为研究特殊应用喷头的洒水分布性能,在前期研制完成超大流量闭式洒水喷头（流量系数K≥400）的基础上,另外选取2种（K-161和K-363）类型的特殊应用喷头,在安装高度为22 m、喷水强度分别为32 L/（min?m2）和36 L/（min?m2）的情况下开展了3种喷头的洒水分布性能试验。结果显示,受喷头溅水盘结构形式和压力波动的影响,喷头的喷水强度偏离度随流量系数的增大而减小,而喷水强度均匀性受工作压力影响较大,工作压力越小,均匀性越好。     

Delayed Fracture of Glass Bulbs Used in Fire Sprinklers

Very rarely, glass bulb sprinkler heads activate when there is no fire or elevated temperatures. In such cases, the bulb fragments are never recovered. Speculation may arise that there was a defect in the bulb from manufacturing or installation, which led to its eventual failure. We investigated the growth of such defects using the principles of fracture mechanics and the well-known laws of slow crack growth in glass. These laws include the existence of a threshold, below which cracks do not grow at all, and above which cracks grow at a velocity that is greater than a minimum value. As a result, bulbs either never fail, or fail within a relatively short time after the crack or defect is created. Finite element and fracture mechanics analyses for a typical bulb indicates that the maximum delay is of the order of hours or weeks, not years. Experiments confirm this phenomenon. Over 100 bulbs were intentionally damaged, then placed under a constant load. A total of 44 bulbs, for which the combination of damage and load happened to be above the threshold for crack growth, failed within days (up to 36 days), while all other 58 bulbs survived over 2 years without failure. The theoretical analysis and the experiments demonstrate that fracture of sprinkler bulbs occurs relatively quickly after the introduction of a defect: if a bulb fractures in service without apparent cause, there must have been some event to damage the bulb or the sprinkler head in the days or weeks before the activation.     

某高架仓库火灾风险数值模拟

利用FDS对某高架仓库火灾风险进行数值模拟,并分析快速响应早期抑制喷头的控火效果,探讨机械排烟形成的负压对火灾蔓延的影响。结果表明,运用快速响应早期抑制喷头可以有效地防止火灾蔓延,而布置货架喷头可以进一步提高仓库的安全性;布置货架喷头时,货架内喷头的动作温度应比顶板喷头动作温度低;加入机械排烟时必须合理计算机械排烟量,避免负压引起新鲜空气进入火场。     

The simulation of fire sprinklers thermal response in presence of water droplets

When a fire occurs, the sprinkler closest to the location of the fire typically activates first and releases water droplets into the rising plume of hot gases. Part of these droplets is entrained by the plume and may impact on adjacent sprinklers providing evaporative cooling and thus delaying their activation. The model of the thermal response of sprinklers in these conditions suggests the introduction of the concept of equivalent cylindrical links: a solid metallic cylinder is said to be equivalent to a given fire sprinkler link if it reaches the activation temperature of the sprinkler at the same time, both in dry conditions and in presence of water droplets carried by the hot gas flow. Tests are conducted on both fire sprinklers and equivalent cylindrical links to validate this theoretical approach. The results compare favorably both in dry and wet conditions for the range of parameters considered in this study. Therefore, this approach enables the transient quantification of the sprinkler thermal response in an actual fire scenario such as a large-scale fire test.     

Simplified Calculation Method for Determining Smoke Downdrag Due to a Sprinkler Spray

A simplified method has been developed to predict smoke behavior subject to a sprinkler spray. The method considers whether downdrag is likely to occur and the distance that smoke is then pulled down should downdrag be present. The method is validated using third party experimental data. Empirical equations are applied in the calculations to determine the heat loss from a smoke layer due to the sprinkler spray and therefore the smoke layer temperature. Comparative results show that the simplified method might expect the onset of smoke downdrag regardless the difference in temperature predictions. The empirical equation to predict the penetration depth of downdrag smoke is based on previous research and compared with third party experimental data. The predicted depths are acceptable for engineering use. For a 15 mm nominal sprinkler the water flow rate that leads to the onset of downdrag for typical smoke layers up to 2 m in depth is less than 100 L/min which leads to an operating pressure being less than 0.16 MPa. Experimentally data for sprinklers other than the 15 mm nominal sprinklers are unavailable and therefore the method should be used with care for any other sprinkler.     

Sprinkler protection of manufactured homes with sloped ceilings using prototype limited water supply sprinklers

Three full-scale fire tests were conducted in a commercial manufactured home 4.3 m wide by 18.3 m long with 10° sloped ceilings. The purpose of the tests was to determine the performance of limited water supply (LWS) sprinklers under a sloped ceiling and to determine whether the minimum distance allowed between sprinklers could be reduced from 2.4 m to 1.8 m. Six prototype LWS sprinklers were installed at a spacing of 1.8 m by 2.4 m in the living room/kitchen area, which measured 4.0 m by 7.2 m. The ceiling and walls were combustible in all three tests, and the room was ventilated by three open windows. The fuel package for all three tests consisted of a vinyl-covered chair with polyurethane padding, double-layered curtains (100% polyester and 50% cotton/50% polyester), and a wooden end table. In the first test, the fuel package was placed in a corner; in the second test, along the wall under the apex of the ceiling between two sprinklers; and in the third test, along the longitudinal wall between two sprinklers. In all tests, no more than two sprinklers actuated. The flow rate with one and two sprinklers operating was 38 pm and 49 pm, respectively. Flow after the first sprinkler actuation was maintained for 10 minutes when one sprinkler actuated and for 7 minutes 40 seconds when two sprinklers actuated. The total flow in each of the three tests was 380. In all three tests, the sprinklers prevented the curtains and wall paneling from becoming involved in the fire during sprinkler operation. Tenability based on carbon monoxide concentration and gas temperature at the 1.5 m level was maintained in all three tests.     

Non-Intrusive Measurements in Fire Sprinkler Sprays

The results of phase Doppler interferometry (PDI) and particle image velocimetry (PIV) measurements to characterize the water sprays produced by fire sprinklers are presented. The large size of the water drops produced by fire sprinklers, and the relatively large coverage area of the spray, present significant challenges when attempting to characterize these sprays. These difficulties are especially relevant when using PDI because large drops and large coverage areas may result in attenuation of the transmitting laser beams. For the fire sprinkler investigated, it was determined that attenuation of the laser beam resulted in over-counting of drops due to burst splitting, a situation in which the Doppler signals from single drops are misinterpreted as being due to multiple drops. This effect was minimized by carefully choosing the operating conditions of the PDI processing electronics. PIV measurements provide velocity profiles that can be used as input for fire dynamics simulations to predict the effect of sprinkler sprays on fires. The results from the PIV measurements show good agreement with the velocity measurements obtained from PDI in the core of the spray, but poorer agreement along the sprinkler axis. The discrepancy was attributed to recirculation zones present in the experimental facility and possible biasing of the PIV measurements towards the larger drops.     

对不同安装高度、工作压力下喷头布置间距的探讨

依据《自动喷洒与水喷雾灭火设施安装》提供的ZST-15型喷头洒水曲线和《自动喷水灭火系统设计规范》(GB50084-2001)(2005版)中的相关规定,分析在保证作用面积内不留洒水空白点和喷水强度的前提下,喷头在不同安装高度、工作压力下所应采取的合理布置间距。