Not really a weapon at all, but a construction tool adaptable for combat. A welding torch needs a supply of burnable gas to work, which makes early versions immobile and gives late versions a very limited endurance.
Elemental (fire)
The weapon has some sort of elemental aspect that increases damage. Anyone damaged by an elemental weapon may take additional damage at the end of the shot. Unless the target has some extra resistance to the damage type (such as fire or acid resistance for those attacks), he takes 3 additional wound points.
Someone immune to melee weapon damage ignores any Wound Points from the weapon itself, but if the attack overcame Toughness/Armor and would have inflicted damage except for the resistance, the target still take the three extra elemental wound points.
A target immune both to the elemental damage and the regular damage takes no damage at all.
Improvised
This weapon does not need to be made as a dedicated weapon - it can be found or scrounged from civilian gear. Such scrounged versions are less durable than the real thing, and break on any snakeyes roll. In addition, any Disarm Stunts get a +3 modifier against such a weapon.
Of course, a purposedly crafted version of the weapon does not have these drawbacks.