Havrik Stoneskimmer
Adventurer
I agree that the wording is unclear, but I think that the gas is meant to fill the east-west corridor, and it activates when the double doors to the north are opened at which point all of the PCs in the hallway fall asleep.
shmoo2's analysis demonstrates that this is less of a deathtrap than it seems at first glance. I didn't realize in my first reading that you only roll for the juggernaut once and then it stops (or goes back into its cubbyhole).
I've never played the original ToH, only the 4e conversion, which is fairly faithful in many places but tends to tone down the "sorry, you all died" instant traps. The juggernaut in that version is a mobile trap that moves in a random direction every round until the PCs flee. So even though the 4e version is neutered in some ways, in other ways this encounter is more deadly than the original, since it continues until the PCs flee the area (and they may well be tempted to explore behind it).
shmoo2's analysis demonstrates that this is less of a deathtrap than it seems at first glance. I didn't realize in my first reading that you only roll for the juggernaut once and then it stops (or goes back into its cubbyhole).
I've never played the original ToH, only the 4e conversion, which is fairly faithful in many places but tends to tone down the "sorry, you all died" instant traps. The juggernaut in that version is a mobile trap that moves in a random direction every round until the PCs flee. So even though the 4e version is neutered in some ways, in other ways this encounter is more deadly than the original, since it continues until the PCs flee the area (and they may well be tempted to explore behind it).