Choking gas

I was hoping someone could tell me a little about how choking gas works. My e/w was hit with it in PvE yesterday and for a short amount of time my spells were all interrupted as soon as I began casting. I tried looking for an icon in the top left so I would know when not to try and cast, but I don't remember seeing one. Can anyone provide a little info or suggestions for dealing with Choking Gas interrupts?

Every time an arrow hits under the effect of choking gas you are interrupted, as is the pbaoe around you.

I'm not familiar with the Preparation skill type so correct me if I'm wrong in assuming Choking Gas works like Conjure Fire in that while active it adds an effect to each attack (but isn't an enchantment). That would make it better than a spell that enchanted a target since the target doesn't know exaclty when Choking Gas is in effect. And I am also assuming that the creature interrupting me was able to do it so quickly because it's an AI controlled opponent. I was consistantly being interrupted casting 3/4 cast time spells, which I'm sure a good player could also do.

When the ranger uses choking gas, all his attacks for the next X seconds will interrupt his target and those standing adjacent to his target, since the preparation only affects the ranger no icon will show on you, because you're only affected when you, or someone standing next to you, are hit by the rangers arrows.
The fact that all you spells got interrupted just shows that the ranger had taken a liking to you.