K.K. Yuen

A preliminary investigation of airflow field in designated refuge floor

Abstract Refuge floor is specially designed in high-rise buildings for the purpose of supplying a temporarily safe place for evacuees under emergency situations. The provision of such designated refuge floor is a prescriptive requirement in the fire code of Hong Kong. Such a provision appears to be desirable by the regulators as it relates to simple rules and has administrative convenience. In order to fulfill its function, the refuge floor should be a safe place for the evacuees. The safeness of refuge floors under fire situations may be impaired if the floor is affected by smoke from lower levels. The code prescribes that cross-ventilation should be provided in refuge floor so as to prevent smoke logging. However, the adequacy of such a measure and the influence of such an open floor on the rest of building have not been analytically studied. An investigation on the airflow around and inside the refuge floor is required and will provide preliminary insight on the airflow and the smoke movement patterns. In this paper, the Computational Fluid Dynamics method is employed to analyze the airflow field around and inside a refuge floor. The aim of this paper is to describe the airflow field in and around a designated refuge floor, which is the first step to explore the wind effect on the safeness of refuge floors. The study shows that airflow could be a factor affecting the smoke flow pattern.

A CFD Study of Buoyancy Effects on Smoke Spread in a Refuge Floor of a High-rise Building

This paper presents a CFD study of wind-smoke spread in a designated refuge floor of a high-rise building and explores the influence of buoyancy on the smoke-flow field. A designated refuge floor is a prescribed requirement stipulated in the Code of Practice on Means of Escape of Hong Kong. It is regarded as an interim safe place for evacuation under fire or other emergency situations in high-rise buildings. In order to prevent smoke logging and causing hazard to the evacuees in the floor, Hong Kong’s code prescribes that cross-ventilation should be provided in such a way that the floor should be open-sided above the parapet on at least two opposite sides. However, whether such requirement is effective has not been analytically studied. A previous study has revealed that smoke may spread into the floor by dint of wind action, and how the buoyancy affects on airflow and smoke is not further studied. We have extended our study and found that the buoyancy could strongly affect the flow pattern. The buoyancy effect could cause a high vertical velocity component inside the refuge floor. The evacuees, while having a rest in the refuge floor, will be substantially affected by the ingress of smoke under a strong wind. It has further been found that the amount of smoke migrating into the refuge floor will be affected by the temperature at the opening of the fire zone immediately below the refuge floor in that it is inversely proportional to the opening temperature.

A numerical study of external smoke spread in designated refuge floor

Designated refuge floor is a prescribed requirement stipulated in the Code of Practice on Means of Escape of Hong Kong. Such a floor is considered as a temporary safe place for evacuees under fire or other emergency situations. To prevent smoke logging in the floor, Hong Kongs code prescribes that cross-ventilation should be provided. However, whether such requirement is effective has not been analytically studied. In a previous study on the air flow field around and inside a refuge floor, it has been revealed that smoke may spread into the floor by dint of wind action, and whether such smoke will be forced to leave the floor or diluted by the inflow of wind should be further studied. This paper presents a numerical study of wind-smoke field for a refuge floor. It was found that the smoke effect will be dependent upon the location of the fire source, the configuration of the opening at the refuge floor as well as the velocity of wind. This implies that the prescribed requirements may not be appropriate in some fire scenarios.

A computer simulation model of emergency egress for space planners

The spatial design of a building affects the movement of occupants. In complex buildings with a large population, such as places of assembly, the movement of people towards the exits under emergency situations is a major concern. Ideally, people should leave the building smoothly under emergency situations. Traditionally the layout design is governed by the building fire codes. However, the building fire codes merely govern the design of the capacity of individual components, and do not guarantee that smooth egress will occur. Full‐scale egress exercises may be needed to examine the layout arrangement in order to understand the layout problem. However, such exercises may be time‐consuming, or may be impossible when the building has yet to be constructed. Therefore, the use of computer models to simulate the egress pattern can assist not only the building designer, but also the facility manager to plan the spatial arrangement as well as to manage the crowd flow during emergency situations. Discusses the use of a computer model for analysing building layout design.

A CFD Study of Air Movement in Designated Refuge Floor

Abstract Refuge floor is used as a temporary safe space for evacuees resided in high-rise building under emergency case, e.g., fire situation. The provision of refuge floor is a prescriptive requirement in the fire code of Hong Kong. Such a provision is desirable by regulators as it relates to simple rules and has administrative convenience. However, the safety of refuge floor under fire situation may be impaired if the floor is affected by smoke from other levels. The code prescribes that cross-ventilation should be provided in refuge floor so as to prevent smoke logging. Nevertheless, the adequacy of such measure and the influence of such open floor on the rest of building have not been analytically studied. In this paper, a Computational Fluid Dynamics (CFD) method is employed to analyze the airflow field around and inside a refuge floor. The aim of the study is to predict the airflow field inside and around a designated refuge floor, which is the first step to explore the wind effect on the safety of refuge floors. The study shows that airflow could be a factor affecting the smoke flow pattern inside refuge floor.

An Investigation of the Impact of Floor Setting on Airflow and Smoke Extraction in Designated Refuge Floor

Refuge floor is used as a temporary place for evacuees residing in high-rise buildings to take a short rest before taking further evacuation under fire case. It is specified as a prescriptive requirement in the Fire Code of Hong Kong to provide designated refuge floors for high-rise buildings. To fulfill its functions, a refuge floor must be a safe place for the evacuees. However, the safety of refuge floors under fire situations may be impaired if the floor is affected by smoke ingress from lower levels. The code prescribes that cross-ventilation should be provided in refuge floor so as to prevent smoke logging. Even with sufficient cross-ventilation, the prevention and/or extraction of smoke logging into the refuge floor cannot be guaranteed. In fact, the airflow pattern and smoke extraction/dilution largely depend on the floor planning in designated refuge floor. A study of the impact of refuge floor settings on the airflow around and inside the refuge floor is required and expected to provide some insight on the smoke movement pattern. In this paper, the Computational Fluid Dynamics (CFD) method is employed to predict and analyze the air movement around and inside designated refuge floor within a high-rise building under different floor plans. The study shows that the floor planning does affect airflow patterns and further the smoke dispersion in the refuge floor.

An Investigation on the Building Officials' Perception for the Use of Performance-Based Fire Engineering Approach in Building Design

Traditionally, the spatial design of a building is influenced by the prescriptive fire safety codes. As buildings develop and become more complex and new materials are used, the prescriptive fire safety rules may not provide an efficient solution to the new building design. A system approach to the design of fire safety in buildings on the basis of performance criteria may be necessary. The recently published fire codes in Hong Kong have recognized the use of a performance-based fire safety engineering approach as a means to demonstrate the adequacy of fire safety design in a building. However, the judgement on the adequacy is made by the building control officials. Whether they believe the use of such a performance-based fire safety engineering approach can provide adequate fire safety level in a building can have influence on promoting performance-based design. This paper discusses the Hong Kong system and a survey on the views of the building control officials. The investigation indicates that the officials, in general, agree with the need of using performance-based approach, in particular to keep pace with the advancement of building technology. However, they have reservations on the adequacy of current tools for fire safety engineering design. Such views are in line with that of the building officials in the United States.

Effects of altitude and inclination on flame spread over poly(methyl methacrylate) slabs

Flame spread experiments over poly(methyl methacrylate) slabs with different inclinations were conducted in Hefei (with an altitude of 29.8 m) and Lhasa (with an altitude of 3658.0 m). It is shown that the flame spreads significantly slower in Lhasa than in Hefei. For steep slabs with inclination angles of 75° and 90°, the preheat length in Lhasa is longer than in Hefei, whereas for mild inclinations (30° and 45°), it is slightly shorter in Lhasa than in Hefei. The peak total heat flux received by the fuel surface is lower in Lhasa than in Hefei. The measured flame temperatures did not present significant difference. This is actually caused by the combined effects of combustion inhibition due to the low oxygen concentration and less soot formation caused by lower ambient pressure and oxygen concentration in the plateau region, which result in less heat loss by radiation. Based on the analysis, it is concluded that the slower spread behavior in Lhasa is mainly a result of the lower heat feedback level to the solid surface.

CFD wind tunnel test: Field velocity patterns of wind on a building with a refuge floor

This paper reports a CFD wind tunnel study of wind patterns on a square-plan building with a refuge floor at its mid-height level. In this study, a technique of using calibrated power law equations of velocity and turbulent intensity applied as the boundary conditions in CFD wind tunnel test is being evaluated by the physical wind tunnel data obtained by the Principal Author with wind blowing perpendicularly on the building without a refuge floor. From the evaluated results, an optimised domain of flow required to produce qualitative agreement between the wind tunnel data and simulated results is proposed in this paper. Simulated results with the evaluated technique are validated by the wind tunnel data obtained by the Principal Author. The results contribute to an understanding of the fundamental behaviour of wind flow in a refuge floor when wind is blowing perpendicularly on the building. Moreover, the results reveal that the designed natural ventilation of a refuge floor may not perform desirably when the wind speed on the level is low. Under this situation, the refuge floor may become unsafe if smoke was dispersed in the leeward side of the building at a level immediately below the refuge floor.

Numerical simulation model of vibration responses of rectangular plates embedded with piezoelectric actuators

A numerical simulation model for random large amplitude vibration control of composite plate using piezoelectric material is presented. The H∞ control design is employed to suppress the large amplitude vibrations of composites plates under random loading. The numerical simulation model is developed and based on the finite element method. The finite element governing equation includes fully coupled structural and electrical nodal degrees of freedom, and consider the von Karman large amplitude vibration. The modal reduction method using the structural modes is adopted to reduce the finite element equations into a set of modal equations with fewer degrees of freedom. The modal equations are then employed for controller design and time domain simulation. In the simulations without control, the value of the linear mode to the nonlinear deflection is quantified; and the minimum number of linear modes needed for accurate model is obtained. In the simulations with control, it is shown that the truncated modes, which are neglected in the control design, deteriorate the controller performance. Generally, the vibration reduction level is not monotonically increasing with the size of the piezoelectric actuator. The optimal piezoelectric actuator size depends on the excitation level. For higher excitation level, optimal actuator size is larger. The H∞ controller based on the linear finite element formulation gives better vibration reduction for small amplitude vibration, but it still gives reasonable performance for large amplitude vibration provided that the piezoelectric actuator is big and powerful enough.