No abstract

SummaryThe extinguishing performance of three dry chemical powders (DCPs) was investigated through a lab‐scale suppression system for liquefied petroleum gas (LPG) fire. The magnesium hydroxide (Mg(OH)2), sodium bicarbonate (NaHCO3), and commercial ABC − MAP powders are used to prepare two groups of samples: raw samples and milled samples. The effect of milling action on the properties of DCPs, such as the bulk density, microstructure, particle size, thermal decomposition, and the extinguishing performance, is analyzed. The density test revealed that the bulk density increased after milling, and the Mg(OH)2 had a lower density than the other powders. The microstructure analysis showed that the milled powders had a smaller particle size and more regular shapes than raw powders. The thermal analysis demonstrated that the powder decomposition process was somewhat similar with a slight difference in initial decomposition temperature and degradation rate. The fire tests proved that the extinguishing efficacy greatly improved after the samples were milled. Moreover, the experiments indicated that the milled Mg(OH)2 was superior in fire extinguishing to the other samples with shorter extinction time and less agent quantity consumed. Based on the results, it can be inferred that the milling action has a significant influence in enhancing the extinguishing mechanisms' efficiency of DCPs.

In the present work, the extinguishing parameters influencing the dry chemical powder system performance were analyzed and optimized using Taguchi design for minimizing the extinction time of small-scale vertical and horizontal gaseous fires. The system-related parameters include the release pressure (0.2 MPa, 0.3 MPa, and 0.4 MPa), the suppression angle (horizontal, diagonal, and vertical), and the release distance (50 cm, 75 cm, and 100 cm). The extinguishing tests were carried out in a lab-scale local application system. In this study, the magnesium hydroxide powder (Mg(OH) 2) was used as an extinguishing agent. The analysis of experimental results showed that the optimum extinguishing conditions for small vertical and horizontal fires were at the release pressure (0.4 MPa), the suppression angle (vertical), and the release distance (50 cm). The analysis of variance indicated that the percentage contribution of extinguishing parameters on vertical fire extinction time was in the following order: suppression angle (44.69%) > the release distance (39.04%) > the release pressure (2.63%). While the order in case of the horizontal fire was as follows: the release distance (66.00%) > the release pressure (17.65%) > suppression angle (12.34%). The confirmatory tests showed that the extinction time at optimal parameters was lower than that achieved in all other experimental tests.

Fire accidents on floating LNG (FLNG) processing facilities are initiated by the uncontrolled gas leaks and then evolved through the successive failure of relevant safety barriers (SBs). This paper develops a methodology to perform comprehensive failure analysis of fire SBs and corresponding consequences in FLNG system using a Bayesian network (BN). Two BN models were constructed and compared, the independent BN and the dependent BN. The BN models were mapped from Event Tree-Fault Tree (ET-FT) diagram. The inter-dependency between SBs and uncertain causal relationships was completely considered in the dependent BN model. The dependent model also investigated the dependency of all SBs on the release prevention barrier (RPB) as the critical and initial barrier of the fire safety system. The probabilities of SBs failure obtained using the dependent BN were less than that of independent BN values. This could be ascribed to the influence of SBs inter-dependency and the model uncertainty due to uncertain relation relationships between managerial and organization factors (MOFs) and functional failures. Among SBs, it was found that the RPB has the highest failure probability. The diagnostic analysis further identified the MOFs as the most influencing factors contributing to SBs failure. The predictive analysis revealed that the large fire with major damage has a higher probability to occur in comparing with other consequences. Additionally, the BN was extended to estimate the risk levels of consequences by integrating the accident probability, accident severity, and escape, evacuation, and rescue (EER) process reliability. The findings indicated that the EER operations have a major influence on the risk level and suggested to be considered for reliable risk level assessment rather than traditional risk matrix.