N.K. Fong

Numerical simulation on cooling of the fire-induced air flow by sprinkler water sprays

Abstract By the air drag and cooling effect of water droplets, the cooling of the fire-induced hot air flow by sprinkler water sprays is studied by using a three-dimensional field modelling technique. This gives a ‘microscopic’ description of visualizing how the sprinkler interacts with a smoke layer. Macroscopic parameters, such as drag-to-buoyancy ratio, convective cooling rate, etc., can be computed accordingly. With such a model, it is possible for the fire-safety engineers to design proper location, type and performance of sprinkler systems. Since experimental data for validating the model are absent, it is concluded that measurement from full-scale burning tests in a sprinklered compartment is needed.

Application of field modelling technique to simulate interaction of sprinkler and fire-induced smoke layer

Abstract The interaction between the sprinkler water spray and the fire induced convective air flow is studied using the field modelling technique. A system of equations describing conservation of momentum, enthalpy and mass is used to simulate the physical picture. Solution of the problem. is divided into two parts: gas phase and liquid phase. In the gas phase, a two-equation k – e model is used to account for the turbulent effect with the solid wall boundary described by the traditional wall functions. Numerical finite difference method is employed to solve the system of coupled non-linear partial differential equations. The equations are firstly discretized by the Power Law scheme and then solved using the Pressure Implicit with Splitting of Operators (PISO) algorithm. For the liquid phase, the sprinkler water spray is described by a collection of water droplets with different values of initial velocity components and diameter calculated from the Rossin-Rammler distribution function. The motion of each...

Fire safety engineering: comparison of a new degree programme with the model curriculum

Abstract The curriculum design of a new degree programme in Building Services Engineering with Fire Engineering Specialism for the local fire engineering professionals in the Hong Kong Special Administrative Region is reported. The programme was approved by The Hong Kong Polytechnic University and offered in September 1997 with an intake of 25 students per year. The aims are to train fire engineers who can handle not only ‘traditional’ fire engineering systems, but also perform the ‘new’ procedure of fire safety engineering hooked up with the development of ‘performance-based fire codes’ in an ‘engineering approach’. Subject contents to be included in a fire safety engineering degree programme are proposed. A comparison of this new scheme with the model curriculum in Fire Safety Engineering is made. Coverage of topic areas on fire engineering and teaching hours are compared. Differences in the curricula have been identified and discussed.

PolyU/USTC Atrium: A Full-Scale Burning Facility -- Preliminary Experiments

The PolyU/USTC Atrium, a full-scale burning facility for atrium fire studies has been constructed at the University of Science and Technology of China (USTC). The atrium will be managed by USTC and the Hong Kong Polytechnic University (PolyU). The construction features of the facility are reported briefly, and further studies using this facility are outlined. Typical use of the facility is demonstrated by several smoke filling tests. The results on the smoke layer interface height were analyzed and compared with those predicted by zone models. It is observed that a zone model can give quite accurate prediction on smoke filling during most of the burning period. Language: en

Constructal design for pedestrian movement in living spaces: Evacuation configurations

Here we show that the configuration of an inhabited area controls the time required by all the pedestrians to vacate the space. From the minimization of the global evacuation time emerges the optimal configuration of the area. This is a fundamental principle for designing living spaces with efficient evacuation quality, and it is demonstrated here with several simple building blocks that can be used as components of more complex living structures: single walkway, corner, and T-shaped walkway. We show analytically and numerically that the ratio of the widths of the stem and branches of the T-shaped walkway has an optimal value that facilitates the evacuation of all the inhabitants. This result is fundamental, and is the crowd-dynamics equivalent of the Hess-Murray rule for the ratio of diameters in bifurcated ducts with fluid flow.

Constructal design of pedestrian evacuation from an area

Pedestrian movement occurs in evolutionary patterns the effect of which is to facilitate the access of people into and out of living spaces (areas, volumes). In this paper, we rely on the philosophy of Constructal design as applied physics, in order to uncover two fundamental features of evolutionary design for pedestrian evacuation from rectangular areas (e.g., lecture halls with seated occupants). First, the paper shows analytically that the aspect ratio of the floor area can be selected such that the total evacuation time is minimal. Second, the shape of the floor area of each aisle can be tapered such that the total evacuation time is decreased further. These two architectural features are confirmed by means of extensive and systematic numerical simulations of pedestrian evacuation, by using two numerical packages (Simulex and FDS + Evac).

Risk analysis of escape time from buildings

Purpose – To model the evacuation time from buildings in the event of emergencies based on occupant load, looking specifically at the exit width as a design parameter.Design/methodology/approach – In this study, transient occupant loads from a simulation model based on a recent study of 34 offices in Hong Kong were used to evaluate the probable risk to evacuees in the case of an emergency evacuation. For this analysis the “door carrying capacity” approach was used, together with probability profiles for the occupant loads at certain exit flow rates. This paper investigates the occupant load profiles as well as the yearly and daily occupant load variations of some typical offices in Hong Kong and examines the fire safety implications of the office building designs from the perspective of the risk to evacuees.Findings – The results show that the building occupant load, occupant‐load ratio, total exit width and specific flow rate at the exit significantly affect the risk to evacuees.Research limitations/impl...

The motion analysis of fire video images based on moment features and flicker frequency

In this paper, motion analysis methods based on the moment features and flicker frequency features for early fire flame from ordinary CCD video camera were proposed, and in order to describe the changing of flame and disturbance of non-flame phenomena further more, the average changing pixel number of the first-order moments of consecutive flames has been defined in the moment analysis as well. The first-order moments of all kinds of flames used in our experiments present irregularly flickering, and their average changing pixel numbers of first-order moments are greater than fire-like disturbances. For the analysis of flicker frequency of flame, which is extracted and calculated in spatial domain, and therefore it is computational simple and fast. The method of extracting flicker frequency from video images is not affected by the catalogues of combustion material and distance. In experiments, we adopted two kinds of flames, i. e., fixed flame and movable flame. Many comparing and disturbing experiments were done and verified that the methods can be used as criteria for early fire detection.

Numerical simulations for a typical train fire in china

Railway is the key transport means in China including the Mainland, Taiwan, and Hong Kong. Consequent to so many big arson and accidental fires in the public transport systems including trains and buses, fire safety in passenger trains is a concern. Numerical simulations with Computational Fluid Dynamics on identified fire scenarios with typical train compartments in China will be reported in this paper. The heat release rate of the first ignited item was taken as the input parameter. The mass lost rate of fuel vapor of other combustibles was estimated to predict the resultant heat release rates by the combustionmodels in the software. Results on air flow, velocity vectors, temperature distribution, smoke layer height, and smoke spread patterns inside the train compartment were analyzed. The results are useful for working out appropriate fire safety measures for train vehicles and determining the design fire for subway stations and railway tunnels.

Solutions to Buoyancy—Drag Equation for Dynamical Evolution of Rayleigh—Taylor and Richtmyer—Meshkov Mixing Zone

With a self-similar parameter b(At) = Hi/λi, where At is the Atwood number, Hi and λi are the amplitude and wavelength of bubble (i = 1) and spike (i = 2) respectively, we derive analytically the solutions to the buoyancy—drag equation recently proposed for dynamical evolution of Rayleigh—Taylor and Richtmyer—Meshkov mixing zone. Numerical solutions are obtained with a simple form of b(At) = 1/(1 + At) and comparisons with recent LEM (linear electric motor) experiments are made, and an agreement is found with properly chosen initial conditions.