Experimental study on smoke flow behaviour under ships’ deck structures in early stages of fire

Abstract

In ships’ cargo spaces carrying vehicles, so called “vehicle spaces”, fire has sometimes taken place and safety measures against such fire is under discussion at the International Maritime Organization (IMO). Early detection of fire is one of the essential elements of such safety measures. Location of fire detectors affects swiftness of detection of fire, and in onshore buildings, fire detectors are generally installed directly on ceilings because there are no obstacles under ceilings and smoke spreads along the ceilings. On the other hand, structures below ceilings, i.e., decks, of vehicle spaces are quite different from those of onshore buildings due to strength members below a deck, such as stiffeners and web beams. The appropriate positions of smoke detectors in a vehicle space, including vertical positions of detectors from a ceiling, has not been well-understood, while the maximum coverage of a detector is determined by an international regulation. In this study, the effect of structures below the ceilings of vehicle spaces on detection of fire has been investigated and the appropriate positions of smoke detectors including vertical positions have been considered, in particular, for smouldering fire sources. For this purpose, a one-sixth scaled deck model was prepared to simulate a part of a vehicle space and fire experiments were conducted using a small-scaled fire source. The effect of the structure on a smoke flow beneath the ceiling was experimentally investigated under the condition that the flow had a weak driving force in a smouldering fire or an early stage of fire. In the experiment, the flow was visualized using a laser and the smoke density expressed with the extinction coefficient was also measured. In addition, a small flaming fire source was used during the experiment, to further investigate a possibility of detection in an early stage of fire. The vertical profiles of smoke density were measured using the laser transmissometer. Furthermore, a smoke flow was visualized using continuous wave laser. As the results, it is concluded that it is appropriate to install smoke detectors at the lower end of the longitudinal stiffener, instead of installing on the ceilings in vehicle spaces.