The characteristics and application of the branched chain explosion of hydrocracking hydrogenation recycle gas and the relevant combustible gases were systematically studied. The explosive limits of concentration

explosive morphology

explosive waveforms and their influence factors were investigated. From the different kinds of explosive morphology and its pressure waveforms

a new idea on compartmentalization of explosive morphology for the hydrocracking hydrogenation recycle gas was introduced.Within the explosive limits

four kinds of explosive morphology (cold flame

deflagration，detonation，and transition from deflagration to detonation) could be compartmentalized and seven explosive zones (lower cold flame zone

lower deflagration zone

lower deflagration transformed into detonation zone

detonation zone，upper deflagration transformed into detonation

upper deflagration zone and upper cold flame zone) could be classified. The different mechanisms for developing the pressure waves of the explosive morphology were explored. Such knowledge is valuable for further studying the relevant system of branched-chain explosion and developing the theory of branched-chain explosion.The minimum ignition energy

the maximum experimental safe gaps

the degree of explosion danger and other explosion characteristics were experimentally determined. This paper also introduces the concept of ‘key components’ and pointes out that it is the key components of H2 and oxidant O2 that ignite explosion for the system consideres here.The references and methods for developing the explosion-proof safety guidelines were proposed. The results will be of significance in preventing accidents caused by mixture gas branched-chain explosion

giving directions to designing explosion-proof electric equipment and fire arresters

supervising the application of the concepts of branched-chain burning and branched-chain explosion to practice.