Fire safety concerns for new architectural features

Architectural Science Review, Dec, 2007

Thesis for the degree of Doctor of Philosophy

Department of Building Services Engineering, Hong Kong Polytechnic University, China

Supervisor: Professor W.K. Chow

Thesis accepted October 2006

Hung Wing Yan

Corresponding Author: Tel: 852 9629 6526; E-mail: joanwyh@gmail. com

Abstract: Many buildings with new architectural features have difficulties in complying with the prescriptive fire codes in Hong Kong. Active updating of existing prescriptive codes and adopting the new approach of performance-based design are essential in the new century. However, both approaches cannot be achieved with a good understanding on the problems inside. Therefore, fire safety concerns associated with new architectural features was studied as the focus of this thesis.

Four popular innovative architectural features--atrium design, double-skin facade (DSF), internal building void (IBV) and ultra-high rise building design--were studied for their hidden fire risks. Methodology included numerical experiments, critical review of fire codes and incidents, application of fire engineering tools including fire models, and full-scale burning tests at a remote site in Northeastern China.

Current fire regulations, particularly requirements on fire resisting construction such as providing intumescent protective coating for steel structure were reviewed and deficiencies identified. The rationale behind the development and some standard fire tests and equal area hypothesis of the fire codes for high-rise buildings were analyzed. The review would give a basis for revising existing codes.

It was found that the existing prescriptive-based fire codes only concerned protecting against accidental fires. They might not be adequate for some premises as shown in the World Trade Center (WTC) incident. Further, it would take time to revise current codes and develop new codes. An immediate action is to protect those buildings with higher chance to have non-accidental fires. A new fire risk assessment scheme was proposed to identify buildings for immediate upgrading their fire safety provisions. The contrast to other common fire safety assessment schemes, the total fire safety concept is included in this new system.

In this thesis, fire safety aspects of atrium buildings were discussed. By studying the configuration of an atrium in a site survey, it was revealed that fire and smoke could spread rapidly in the atrium space and adjacent levels, leading to life losses, human injuries and property damage. It was also found there are no tailor-made codes or regulations specifying the fire safety requirements for atria. Having considered three fire scenarios, including fire at the atrium level, fire at a shop adjacent to the atrium at lower levels, and fire at a shop adjacent to atrium at upper levels, high headroom sprinkler following the fire services installation code was found not necessarily ti be capable of controlling atria fires.

Fire safety of the IBV design for high-rise buildings was studied by covering fire in a room adjacent to the internal void, spreading of smoke from the fire level to adjacent levels, and fire resistance provisions for windows. For a typical bathroom in a domestic building in Hong Kong, of size 2.25m x 1.55m x 3m with an opening 0.6m wide and 1 m high, the heat release rate (HRR), from Thomas equation, needed for such small room is only 0.5 MW which is a value easily obtained by materials stored inside the room. Fire models including application of Computational Fluid Dynamics (CFD) were used for the analysis of an IBV connected with two levels of bathroom. The CFD study from the literature includes five scenarios varied with opening conditions and pressure differential. The most undesirable fire scenarios happened when there was a negative pressure imposed at the door of the upper room. Results of the study indicated that there might be possibility of spreading hot smoke or even flame from the fire level to adjacent levels through the IBV.

The fire hazard of DSF was examined experimentally. Flame impingement onto the inner glass panes on adjacent floors and cracking appeared on the internal layer of a DSF would be the most undesirable scenario. Full-scale burning tests on part of a full-scale DSF design were carried out in a facility developed in Northeast China. Four tests were performed to demonstrate how the depth of cavity of a DSF affects smoke movement. Cavity depths of 1.5m, 1m and 0.5m were examined. Surface temperature and heat flux received on the test panels were recorded. By comparing the measured surface temperature of the inner and outer glass panels, possible smoke movement pattern inside the air cavity were estimated. Cracking patterns found on the glass panels were also observed. The first cracking occurred when the bulk glass temperature ranged from 120[degrees]C to 350[degrees]C and the heat flux was higher than 3 kW[m.sup.-2]. It has good agreement with the other studies in which the first cracking occurred when the bulk glass temperature was at about 110[degrees]C and the heat flux was about 3 kW[m.sup.-2]. Results showed that a deeper cavity might give better safety under the scenario studied. The outer glass panel would be broken rapidly for the cavity of 0.5m deep but DSF with a cavity of 1.0m deep appeared to be the most risky as glass panels above broke the most frequently among the different cavity depths. The inner glass panel might be broken before the outer panel, leading to an undesirable fire scenario.