在现代火灾环境中快速灭火

随着新型建筑结构的兴起,消防界人士有责任及时发现各种变化,重新审视处置火灾的方式方法,从重新设计,到检查、紧急医疗救助以及灭火等.     

Modelling of hydrogen cyanide formation in room fires

A chemical kinetics model for calculation of the formation of hydrogen cyanide (HCN) has been made. The combustion of a mixture of methylamine and ethylene has been modelled using the stationary laminar flamelet concept. The flamelet calculations are based on several thousand elementary reaction steps including the chemical kinetics of HCN in combustion. The flamelets for both cold (293 K) and hot (1000 K) combustion product recycling have been calculated. The effect of strain is also included in the flamelet calculations. Scalar dissipation rates from 0.01 s⁻¹ to extinction values have been varied. Also the effect of radiation is included in the flamelet state relationships.

Separate flamelet sets for various levels of radiation, from adiabatic up to 30% radiation losses, incremented by 1%, have been made. In the flow field calculation, the flamelet options may be used either as adiabatic, constant radiation or an interpolation between flamelet sets of different radiation.

The chemical kinetics model, incorporated into a Reynolds-Averaging Navier–Stoke (RANS) type CFD code, has been used to simulate two laboratory fire tests of the combustion of nylon. Changing the size of the opening in the test room varied the ventilation between the two tests. Flamelet sets for a mixture of methylamine and ethylene with nitrogen content close to that of nylon were used in these simulations. The simulations were made with and without recycling the combustion products back to the fire.

The calculations show that recycling of the combustion products to the fire increases the formation of HCN and CO. Similarly, a lowered ventilation rate increases the formation of these species. The calculated temperatures and main species concentrations, including HCN, agree reasonably well with the trends in the laboratory measurements.     

Nonlinear analysis of the backdraft phenomenon in room fires

The backdraft phenomenon in room fires is a typical example of nonlinear behavior. In this paper, a simplified mathematical model of the backdraft phenomenon is established based on energy balance equation and the dimensionless model equations are presented using concepts of nonlinear dynamical system theory, the nonlinear dynamical mechanism is analyzed, and the relationship between system control variables and fire conditions is studied.     

Minimum water requirements for suppression of room fires

In many areas, it is essential that no water be wasted in fighting fire. How much water is needed to extinguish typical room fires? This is the question the authors sought to answer in the experiments reported here.     

Estimating room temperatures from fires along walls and in corners

Determination of temperatures associated with room fires provides a means of assessing an important aspect of fire hazard: the likelihood of the occurrence of flashover. Layer temperatures in excess of 600°C have been associated with the occurrence of flashover. A data correlation has previously been presented to estimate layer temperatures for fires burning in the center of rooms. For fires in corners and along walls, restricted entrainment results in higher layer temperatures than predicted by the previous correlation. Modification factors for the previous correlation are developed to extend its applicability to wall and corner burning geometries. The present analysis suggests that a fire in a corner may cause flashover with only half the heat release rate necessary for a fire burning in the center of a room. Reference: Frederick Mowrer and Robert Williamson, Estimating Room Temperatures from Fires along Walls and in Corners,Fire Technology, Vol. 23, May 1987, pp. 133–145.     

Rise in structural steel temperatures during ISO 9705 room fires

An experimental programme was undertaken to study the temperature rise of protected and unprotected structural steel during a fire within a small enclosure (an ISO 9705 room). The fuel (wood crib) was placed at two locations (front and back) within the ISO room. Each location had two fire scenarios present: the first fire scenario was for recording the temperatures of protected steel members within the enclosure, and the second fire scenario was to measure the temperatures of the directly exposed members. Six steel columns and two steel beams were strategically placed, and their temperatures were measured. Other data recorded were gas temperatures and heat release rates (HRRs). Thermocouples were kept in identical locations during the tests with protected and unprotected steel members to facilitate direct comparison. Despite the natural variability in fire development in identical situations, data up to ≈20 min were found suitable for direct comparison between protected and unprotected steel members. Comparison of these results with Fire Dynamics Simulator (FDS) version 5.3.1 modelling (with prescribed HRRs) results is presented to show the usefulness of the data collected.     

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.     

Thermal response of sprinklers — A theoretical approach

Expressions are derived for the element temperature and the sprinkler operating time under standard test conditions. Two types of test are considered, the plunge test, in which the gas temperature is represented by a step function, and the ramp test in which the gas temperature increases at a constant rate. It is shown that the time constant measureed in the plunge test differs from that measured in the ramp test. Expressions are also derived for the delay in sprinkler operation due to the latent heat of the solder.     

Thermal response of sprinklers Part 1. FRS heated wind tunnel

The Fire Research Station has designed and built a heated wind tunnel in order to study the behaviour of sprinklers during the early stages of a fire when they are subjected to convective heating and low gas velocities. This paper describes the development and performance of the tunnel and its use for both rate of rise of air temperature and ‘plunge’ type tests on sprinklers. It may also be used for simulating actual or required fire scenarios. Results of the work using the tunnel are being used as a background to a British Standard specifying the requirements for sprinklers for life safety use. The paper will be useful to those involved in the specification of sprinklers for both life safety use and for the protection of high hazard storage.     

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.     

Effects of foamed plastic insulation on severity of room fires

The results of a series of full scale room burn experiments with foamed plastic insulation in two walls indicate that the severity of room fires as characterized by the normalized heat load does not appear to be increased by the addition of foamed plastic insulation. Note: A condensed version of this paper was presented at the Fall General Meeting and Conference of the Rigid Polyurethane Foam Committee, the Society of the Plastics Industry of Canada, Quebec City, 18–20 September 1984. K. K. Choi is a Fellow of the Society of the Plastics Industry of Canada. Reference: K. K. Choi, Effects of Foamed Plastic Insulation on Severity of Room Fires,Fire Technology, Vol. 22, No. 1, February 1986, p. 5.     

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.     

腔室火灾烟气向远距离房间的传播迁移

利用数值模拟方法研究了腔室火灾产生的烟气通过毗邻的走廊向远距离目标房间传播迁移的规律。结果表明,烟气到达走廊弯处远距离目标房间的时间接近或少于到达某些中间位置房间的时间,有些远距离目标房间中烟气的下降时间反而短。这就解释了遇难者大量死于远距离处的主要原因。     

Effectiveness of sprinklers in reducing fire severity

The effectiveness of sprinklers is examined by comparing fires they extinguish or control with fires they fail to extinguish or control. It is shown that sprinklers substantially reduce the probability of fire area exceeding 100m² but that they normally have little effect until the fire area reaches 3 m². The effect, of sprinklers on the incidence of damage to the building fabric is also looked at.

This paper is part of a research study aimed at developing quantitative fire engineering methods for the assessment of fire risk. The results will be used to calibrate the mathematical models on which these assessments are based.     

Thermal response of steel framing members in open car park fires

For open car park structures, adopting a performance-based structural fire design is often justified and allowed because the fire does not reach flashover. However, this design approach requires an accurate assessment of temperatures in structural members exposed to car fires. This paper describes a numerical study on the thermal exposure on steel framing members in open car park fires. Steel temperatures are computed by the coupling of computational fluid dynamics and finite element modeling, and by analytical models from the Eurocodes. In addition, the influence of galvanization on the steel temperature evolution is assessed. Results show that temperatures in unprotected beams and columns are influenced by the section geometry, car fire scenario, modeling approach, and use of galvanization. Galvanization slightly delays and reduces peak temperature. Regarding the different models, CFD-FEM (CFD: computational fluid dynamics, FEM: finite-element method) coupled models predict lower temperatures than the Hasemi model, because the latter conservatively assumes that the fire flame continuously touches the ceiling. Further, the Hasemi model cannot account for the effect of reduced emissivity from galvanization on the absorbed heat flux. Detailed temperature distributions obtained in the steel members can be used to complete efficient structural fire designs based on the member sections, structure layout, and use of galvanization.     

Protecting fire fighters exposed in room fires: Comparison of results of bench scale test for thermal protection and conditions during room flashover

Heat flux conditions measured in seven room fires are discussed. The conditions varied from just below flashover in a sparsely furnished bedroom to flashover and severe postflashover fire in a typically furnished recreation room. These heat flux conditions are compared with the protection level provided by fire fighter turnout coats conforming to NFPA 1971,Protective Clothing for Structural Fire Fighting. This standard requires that the turnout coat or pants assembly must protect the wearer against second degree burns when a heat flux of 84 kW/m² (2 cal/cm².s) is applied to its outside surface for a minimum of 17.5 seconds [thermal protective performance (TPP) of 35]. The results imply that fire fighters have only ten seconds or less to escape under most flashover conditions. However, the turnout coats provide good protection in many other fire situations. Practical definitions for flashover are given, and possible means for making the TPP test more relevant for research and development work are discussed.     

Mechanical response of a partially restrained column exposed to localised fires

Recent trends in structural fire engineering research have focussed on the response of buildings with large open plan spaces to so-called travelling fires. These fires travel horizontally across the floor plate of a building and result in time and spatially varying thermal exposure and response of the structure to the fire. What has received little attention, however, is the effect that non-uniform thermal exposure has on columns. Recent tests conducted at SP demonstrated the effect of a small non-uniformity of thermal exposure, resulting in a thermal gradient of around 1 °C/mm, on a column exposed to a pool fire. The curvature resulting from a non-uniform thermal exposure where the column is pinned, or in cases where the column is partially restrained, will result in an eccentricity in the column’s loading and large second order effects.This paper describes the effect of thermal exposure varying in both the horizontal and vertical axes to columns by means of including this thermal boundary in a solution of classical Euler beam theory. The resulting solution allows for a variation in the stiffness of the rotational restraint at both ends of the column and a non-uniform temperature exposure through the column’s section and along its height. The resulting equations help to understand better the impact of the assumptions of ‘lumped capacitance’ on steel columns, suggesting a challenge to this assumption in some instances, as well as to enhance understanding of the impact of non-uniform fires on steel columns.     

复合墙体室内温度响应研究

针对建筑物内人体的热舒适性与内墙壁面温度的相关性,建立了具有复合材料墙体的房间内温度响应的数学模型.结果显示,在相同的加热(制冷)条件下,由相同材质、相同尺寸组合构成的复合材料墙体,在不同的材料排列方式情况下,室内的温度响应有很大的不同,这对间歇性供热(冷)房间内人体的热舒适性有较大的影响.     

Fast response method for undamped structures

The conventional modal method in structural response analysis converges very slowly with respect to the number of natural modes. The convergent property is improved by using the condensed stiffness and mass matrices of the system. Thus, less natural modes are required and the difficulties of computing high natural modes are avoided. Undamped response due to deterministic and random excitations are discussed and numerical examples are given.