International Journal on Engineering Performance-Based Fire Codes, Volume 5, Number 1, p.1-5, 2003 1 OBSERVATION ON THE TWO RECENT BUS FIRES AND PRELIMINARY RECOMMENDATIONS TO PROVIDE FIRE SAFETY W.K. Chow Department of Building Services Engineering, The Hong Kong Polytechnic University, Hong Kong, China (Received 18 December 2002; Accepted 7 January 2003) ABSTRACT Consequent to two recent fires in double-deck buses which burnt away almost everything within 10 minutes, some citizens in Hong Kong are now questioning whether they are safe while travelling on a bus. Key points for consideration on providing fire safety in local buses are discussed. Possibilities of flashover will be analyzed with reference to materials fire safety. By using tested results on a sandwich panel sample commonly used in the construction industry with a cone calorimeter, how incident thermal radiation heat flux would affect the fire behaviour of the materials will be studied. It is recommended that tests on those sandwich panels with or without fire retardants treatment under higher external heat fluxes, say at least 20 kWm -2 for a flashover fire, should be developed to understand how the materials would behave in a fire. Before such tests are agreed by the interested parties, immediate actions to take on fire safety management are recommended. 1. INTRODUCTION Consequent to two big bus fires happened recently [e.g. 1,2], people in Hong Kong are wondering about whether they are safe while travelling on a bus. It was reported that only part of the bus envelope wall and the engine chassis were left after the fire had started in a double-deck bus in just 10 minutes [e.g. 2]! Fire safety for buses should be understood more and being pointed out in this short article. The percentage by weight of plastics for modern vehicles had been increased up to 13% by weight for private cars as reviewed in 1994 [3]. Modern buses also used quite a lot of composite materials with adhesive resins. To provide proper fire safety protection to a bus, those combustible items must be selected carefully. Upon ignition of combustible materials by accident such as electrical fault, a bus fire is similar to a compartment fire which happens at least in three stages: the growth stage; the development stage upon transition to flashover; and the decay stage. Air-conditioned buses are of enclosed structure, smoke generated would fill up the space quickly as reported earlier which is another point of concern to be addressed separately. Those bus envelopes are made of thermal insulation materials such as glass fibre reinforced plastics. The organic resins can be over 50% by weight eventhough the surface of the panel might be metallic. The overall heat transfer coefficient [4] of those modern bus envelopes during a fire will be much lower than those values for traditional buses with sheet metal, giving easier conditions to flashover. There should be higher expectation on fire resistance requirement of the bus wall, especially on satisfying the stability and integrity criteria. Fire safety in double-deck bus had been reported in the literature [5-9] as such a bus fire started from the engine at the rear happened two years ago [e.g. 10]. Desired fire protection goals [11] for a bus had been outlined and the following were discussed [5-9]: y Fire safety materials. y Bus fire scenarios. y Smoke filling in the bus compartment. y Brief review on the heat release rate of a burning bus. As there were no other bus fires since then [e.g. 10], nobody was interested in that incident anymore. However, two big bus fires happened recently within 2 months [1,2] and more citizens are now questioning about bus fires. The objective of this paper is to clarify several points as raised by the media [2]. 2. COMBUSTIBLES FOR BUS Apart from the fuel and its associated system, combustible items are envelope as lining materials, seating materials and materials for air ducts for air- conditioned buses and plastics components of the vehicle. The amount of combustibles and their orientations are important in affecting how the materials would be burnt. That is why some fire tests are specified on testing not only the materials, but also their assemblies. Flammability, smoke emission and toxicity of those materials are the key