Flame Thrower is an Elemental weapon.
Flame Thrower has very short range, but launches fire and ignites enemies. If it's on high level only few seconds are needed to kill an enemy. It has high rate of fire. But the fire it produced can be dangerous for player's squadmates or the player. Never fire targeting below yourself.
There is a secret achievement on Ice Caverns map and it requires the Flame Thrower to complete. Use Flame Thrower to burn an ice rock that looks like a foot and you will get the "Cold Feet!" achievement.
Flame Thrower also has a custom version, Afterburner.