Does Fire Dart damage stack?

They do 100-150 damage each, but its damage over time. I was wondering if this damage stacks? If i shoot 2 fire darts one after another at an enemy, will it accumulate to 200-300 damage, and 3 to 300-450 damage, and so on? If there is a stack, is there a limit to the stack? Or no stack at all? 

thanks