How did Weyland make that flamethrower?

[gameoverman]

It looks like he used his ventilator. 

[Vader the White]

You just answered your own question.

[Dingo]

Is the stuff inside his inhaler/ventilater flammable? I didn't think they were.

[Vader the White]

It was air, which can fuel fire and it pushed the fire towards Scar.

[cygnus]

It's the propellant used to create the pressure inside the tank. Depending on the chemicals used, and whats inside it, the contents could also be flammable. The Oxygen inside the ventilator would sure as hell help too

[gameoverman]

I doubt oxygen would create a flame like that.  Flamethrowers use a type of flammable gas or liquid.  Oxygen can fuel a fire but not propel it in such a way as don't forget the atmosphere also contains oxygen.

[Dingo]

Yea, typically a gust of wind would take out a out a flame that big.