Preliminary Result on Unconfined Vapor Cloud Explosion using Vertical Tube on Hot Surface

The unconfined vapor cloud explosion (UVCE) is fire accidents that could cause severe damage and it sometimes leads to high potential of casualties. Severity caused by UVCE is due to its wide spread fire explosion and that the source mostly comes from a relatively small amount of gasoline or gas leak that has happened long enough leading to the occurrence of an explosion. Since the awareness to this situation relatively low. Research on flammability levels from various liquid and gas fuels has been conducted extensively and it has even been shown in MSDS which ease users in utilizing fuel handling and the selection of safety factors. There have been many studies completed on discovering the cause of fire occurrence especially after the incident of several UVCE-related accidents. Similarly, many dispersion models of fuel leakage and liquid followed by evaporation process have been developed at an applicable level. UVCE still leaves some questions related to the initiation of the explosion. Some research on the phenomenon of explosions on UVCE has been carried out to find out the conditions so as to enable an explosion. Moreover, there is still one question unanswered on UVCE concerning on how do high velocity of deflagration arises in the conditions of an open space explosion. From an accident evaluation so far, it can be believed that the obstacle in the flame path will make the escalated flame velocity reach the Deflagration to Detonation Transition (DDT) level. This was supported by the results of a large scale experimental study conducted by several researchers whose results were reported in line with these assumptions. In addition, some researchers believe that the explosion of UVCE is sequential, beginning with the initial fire. The flame formed will generate heat quickly through radiation heat transfer to the unburned vapor cloud section. This phenomenon is considered responsible for the occurrence of a larger explosion and covers a large area on several accidents. This paper presents preliminary results from lab scale research to characterize the deflagration velocity of vapor cloud flame which is affected by the temperature of the environment. Visual observation is processed from the camera record on deflagration in an open vertical tube with a hot plate. By using gasoline as a vapor cloud source, tests were carried out in three conditions: lean mixture, stoichiometric mixture and rich mixture. In experiments with lean mixture does not occur or it is difficult to fire. For stoichiometric mixture, deflagration occurs quickly and causes an explosion sound. In rich mixture conditions a loud explosion occurs. Especially for the 1.8 stoichiometric concentration, two fires were produced and with the loudest explosion sound. On first fire combustion occurs quickly with a large fireball, after which a second explosion is followed which depletes the rest of the unburned vapor cloud. In experiments with very rich mixture (concentrations of 2 x stoichiometric conditions) occur fire with a slow flame velocity and form soot significantly.