The cabin fire protection concept was widely used in the retail area s of many public transport terminals in Southeast Asia since 1990 . Fire environment in a ‘bare cabin’ was studied experimentally in a big burning hall. The objectives are to understand the possible fire environment in such design for providing useful d ata in deciding suitable fire services installations. A cabin of leng th 4 m, width 4 m and height 3 m was constructed with limited ventilation supplies adjusted by the door size. Pool fires with heat release rate up to 1 MW were considered. Eight of the tes ts carried out will be reported in this paper. 3 1. Introduction The “cabin” concept (1) has been used widely for fire safety protection in many big halls in Southeast Asia including Hong Kong including many terminal buildings (e.g. 2,3). Generally spe aking, the ‘cabin’ concept is a good design to protect the areas of high fire load in big halls and allow better space allocation. However, fire services provisions, at least a workable sprinkler system and a smoke management system, must be installed and designed properly under agreed design fires. There are concerns (4,5) on whether the sprinkler system can control fires at low values such as 2 MW in the retail areas. Because of the cabin roof that confines heat and smoke, flashover would occur if th e sprinkler and smoke extraction systems fail to work. Also, smoke would come out of the ‘open’ design if the smoke extraction system does not work properly. Note that the objective of installing a sprinkler system is to control the fire at a certain val ue, not to extinguish it completely. In case of the sprinkler and s moke management system fail to work, a fire in a cabin, defined as a ‘bare cabin’ fire, would become a big burning object with large air entrainment rate to give very high smoke production rate. Smoke would then spread quickly to its adjacent areas. Thes e were pointed out in theoretical studies on analyzing flashover criteria (6) for a cabin fire (7), smoke filling process in an atrium, and smoke extraction system performance (8) and othe rs (3). However, experimental data are absent in the literature for fires of high heat release rate to demonstrate the real physical picture of a ‘bare cabin’ fire. Preliminary experimental studies of ‘bare cabin’ fires were carried out in a burning hall , the Fire T est Atrium , at the State Key Laboratory of Fire Science, University of Science and 4 Technology of China (USTC) . Experimental data for understanding cabin fires in an atrium were obtained through full -scale burning tests (9,10). The target is t o provide useful information for the building operation team and als o the design engineers for assessing this fire safety design for the atrium. In this paper, only fire in a cabin itself, i.e. bare cabin, was studied. Consequences of such a fire for the atrium were reported separately (11-13). 5 2. Experimental Design For a cabin with high fire load and adequate ventilation, flashover would occur quickly to give a fully -developed fire (e.g. 14,15). There are difficulties in designing flashover experi ments, since the study would destroy the testing facility. However, it is necessary to carry out such studies (16). By referring to different experiments and flashover studies reported in the literature such as the crib fire experiments in a room (17), flashover fire experiments in a full -scale testing facility (18), and smoke filling process experiments in an atrium (9,10), and taking into account the requirements of a ‘bare cabin’ fire, a cabin similar to a retail shop in a terminal hall was built with a photograph shown in FIG. 1a. The geometry is of length 4 m, width 4 m and height 3 m as illustrated in FIG. 1b. The roof and the walls were made of sandwich fireproof plasterboard, with overall thickness of 7 cm. Ventilation can be provided by a doo r and also adjustable vents: • The door was designed with adjustable size. • There are four vents of 18 cm high at the bottom of the cabin. Area of those vents can be changed . • Window located in the wall opposite to the door can also be taken as a vent if necessary. There are four steel wheels installed at each corner of the cabin for moving to different places of the atrium. For the experiments described in this paper, the cabin was located at the centre of a burning hall of length 22 m, width 12 m and h eight 27 m. Diesel with heat of combustion 46000 kJkg-1 was used as the burning fuel in the experiments. 6 Diesel is difficult to ignite but would produce large quantities of smoke so that visual inspection of the smoke filling process can be carried out e asily. A small amount of gasoline was added for easier ignition. T hree pool fires labeled as PC1, PC2 and PS1 were: • PC1: A circular pool fire of 0.59 m diameter • PC2: A circular pool fire of 0.975 m diameter • PS1: A square pool fire of size 1 m by 1 m A total of eight pools were made and put together to give bigger fire s. The heat release rate Q was calculated from the transient mass loss rate m , the combustion efficiency  and the heat of combustion H: Hm Q= … (1) The maximum heat release rate of a single pool was 1.5 MW. 7 3. Experiments The following were measured in a ‘bare cabin’ fire: • Mass loss of fuel: Mass of fuel was measured by a six -fulcrum electronic balance with output converted to channel voltage s ignal. The maximum weight was 50 kg and the precision was 0.1 kg. The balance was lagged with thermal insulating materials. The pool was supported by fireproof fibre glass in the pool boards to keep each fulcrum equally weighted. • Temperature distribu tions inside the cabin: Horizontal and vertical distributions of tem peratures in the cabin were measured using thermocouples. There were three racks of thermocouples in the cabin as shown in FIG. 2: - Rack I: There were 10 T -type thermocouples distribute d vertically with intervals of 5, 20, 20, 20, 20, 20, 20, 30, 30 cm from the cabin roof. They were placed at 35 cm from the north wall, and 30 cm from the west wall. - Rack II: Similar to Rack I with 10 T -type thermocouples, placed at 90 cm from the sout h wall. - Rack III: There were 9 K -type thermocouples mounted in the east wall, and arranged as a T - shape with five thermocouples placed horizontally and four placed vertically. The 8 top five thermocouples labeled as 1 to 5 were put at 40 cm horizontal int ervals from each other, and 5 cm down the ceiling from south to nort h. The middle four thermocouples labelled as 6 to 9 were arranged with the same vertical intervals which can measure temperature through a manual meter thermocouple. • Heat flux: A heat fl ux meter was employed to measure heat flux at 30 cm above the ground . The heat flux was proportional to the voltage output with a coefficient of 18.85 kWm-2mV-1. Video facilities were used to record and observe the burning processes. Detailed arrangement of the instrument is shown in FIG. 2. 9 4. Typical Experimental Res ults Many tests were carried out and eight of them are reported in this paper. The ventilation conditions were changed by varying the area of the door and vent size at the bottom of the cabin. A summary of the tests is shown in T ABLE 1 together with the door size. The ventilation conditions at the bottom vents were: • East and west: Either open with height 0.18 m and area 0.72 m2; or closed. • South and north: Either open with height 0.18 m and area 0.54 m2; or closed. A typical burning test such as test 5 is shown pictorially in FIG. 3. There, the fire source was a PC2 circular pool of 97.5 cm diameter with 6.1 kg of diesel oil. The vent at the bottom of the cabin was closed, and the d oor vent was 58 cm high (excluding the bottom vent of 18 cm high). The west door of the big hall was fully open to supply adequate air for complete combustion. All other windows and natural vents of the hall were closed during the experiment. Key resu lts for the eight tests are summarized in TABLE 1. The ventilation condition, maximum heat release rate Q max, flashover time using various temperature criteria, maximum mean temperature of the hot smoke layer in the cabin T g, and flashover time using heat flux criteria are shown. Horizontal and vertical temperature dis tributions of the hot smoke layer for test 4 are shown in FIGS. 4a and b. Temperature did not vary much in the horizontal direction, while varied quite a lot in the vertical direction. The transient average temperature of the hot smoke 10 layer at 5 cm away from the ceiling for test 4 is shown in FIG. 5. The temperature increased significantly at about 200 s. A maximum temperature of 660 C was recorded 20 s after that, which indicated the occ urrence of flashover. 11 5. Observations The following were obser ved: • By comparing Qmax and T g in test 4 with other experiments, the larger the heat release rate, the higher the temperature of the hot smoke layer in the cabin.  Ventilation conditions affected flashover significantly. Under the same condition of pool size and fuel mass, flashover occurred in test 5 with a maximum temperature of 558C; but flashover did not occur in test 2 and the maximum gas temperature T g was only 415C. Note that t he conditions of the bottom vents were the same for the two tests. However, the door area was 0.93 m2 for test 5 and 2.35 m2 for test 2.  Smoke temperatures in the cabin would be affected by the ventilation conditions. Higher maximum T g of 662C was foun d in test 4, where all the bottom vents were open, and the door area was 1.63 m2. If the number and area of the ventilation openings increased, smoke temperature would be lowered. For test 2 with all the bottom vents open and a door area of 2.35 m2, maxi mum T g was 415C. While in test 5 with all the bottom vents open an d a door area of 0.93 m2, maximum T g was 558C. Therefore, higher heat release rate is required for flashover.  From tests 7 and 8 with all the bottom vents closed, smoke layer temperatur e increased as the ventilation factor of the door v vH A increased. For test 7, v vH A was 12 0.71 25m and maximum T g was 531C. But for test 8, v vH A was 0.98 25m and maximum T g was 536C.  Test 3 was performed with water added to th e pool fire. Adding water to the pool would affect the burning process significantly. Comparing test 3 with test 4, the heat release rate of the former case was much lower than that of t he latter case with water added. The effect of adding water on the heat release rate is still unknown.  It is observed from experiments that the burning rate increased suddenly for the eight tests. A possible explanation is due to the thermal radiation from the hot smoke layer to the pool fire. As a result, flashover occurred. However, this was not indicated by the smoke layer temperature in other tests. This suggested that using only the smoke temperature criterion (550 C or 600C) to determine flas hover may not be sufficient. 13 6. Analysis The minimum heat releas e rate for flashover Q max was found to be correlated with the ventilation factor (e.g. 1 4,16,19). This can be used to check with the results measured in this study. However, there are se veral openings for tests 1 to 6. The total ventilation factor ( T TH A ) of equivalent height H T, width W T and area A T (= HTWT) for each test calculated by assuming that the proportionality constant relating air flow rates and ventilation factor are the same for all openings. If the ith opening is of wid th W i, height H i, area A i and ventilation factor i iHA , then for N openings, the total ventilation factor T TH A is:  ==N 1ii i T T HA H A … (2) Valu es of flashover heat release rate Q Thomas calculated by the equation proposed by Thomas (14), but included as a computer program in the fire engi neering design tool FIREWIND (20 ), are shown in TABLE 1 as well. 14 7. Conclusion Preliminary experiments on bar e cabin fires were carried out. It is observed that flashover occurs easily by burning a very small amount of diesel. Note that many ‘open cabins’ are constructed for retailing in public transport terminals in the Far East. Igniting the huge amount of comb ustibles stored might lead to very big fires. The following are s uggested to be studied for assessing fire safety of those cabin designs:  To study the relationship between the fire heat release rate, smoke layer temperature and the ventilation factor.  To study the smoke filling process due to a cabin fire in an atrium, and compare it with the smoke filling process of a fire in an atrium.  To study the effects of sprinklers, natural ventilation and forced ventilation on cabin fire and smoke filling proce ss in an atrium. Appropriate fire services installations can then b e decided to control the design fire to a more realistic high value. Most of these items are being studied as doctoral degree projects and report ed (21,22) . 15 8. Additional Comments The paper was pub lished as a journal paper (23). With the practice of publisher, preprint i s allowed to upload at a website. There are furth er studi es on this topic (24,27-34,38,39 -40,42 - 43). Additional f ire services installations such as long throw sprinklers are installed , see ( 25- 26,36 -37,45). Fire safety management is a key part in providing safety , see ( 35,39 ,41,44,46 - 51). Acknowledgement This project is supported by the National 973 project “ Fire Dyn amics and Funda mentals of Fire Safety” under Subgroup 4 “Smoke Movement and Toxic Harmful Gases Transfer in Fire” with number 2100CB40960 4, People’s Republic of China . 16