The severity factor is a common term used in steam explosion (SE) pretreatment that describes the combined effects of the temperature and duration of the pretreatment. However, it ignores the duration of the explosion process. This paper describes a new parameter, the explosion power density (EPD), which is independent of the severity factor. Furthermore, we present the adoption of a 5m(3) SE model for a catapult explosion mode, which completes the explosion within 0.0875 s. The explosion duration ratio of this model to a conventional model of the same volume is 1:123. The comparison between the two modes revealed a qualitative change by explosion speed, demonstrating that this real explosion satisfied the two requirements of consistency, and suggested a guiding mechanism for the design of SE devices.