As reported in previous research studies (Cooper et al., 1986; 1994), Fig. 8 shows that p1 increases with increases in pv. In addition, the excess pressure p1pv, which is in a range of several kilopascals, is approximately that of Cooper et al. (1986) but is much less than that of Kasmani et al. (2007) and Kumar et al. (1989). This difference may be caused by many factors, for example, the usage of a duct, the burning rate of gas mixtures, and the vent area. In current study, p2, which is nearly independent of pv forpv> 0 kPa, is always approximately a few kilopascals, which is consistent with the finding of McCan et al. (1985).