Flame Thrower Secondary Ability - Blast

I was thinking about the effectiveness of the flamethrower and how it can a marine survive when under pressure by a fade or other attack. Sure the flamethrower reduces their power ability but the marine is still very vulnerable.

Perhaps the flamethrower could have a secondary ability where it blows out in a single burst and does varying levels of damage depending on proximity. The burst forces back any aliens in the line of sight, giving a short period of time to retreat or manuever.

To reduce its effectiveness this blast could reduce the amount of ammo by a half or a quarter of a tank.

Thoughts?