Quote Originally Posted by Being View Post
Propofuckingganda, Hydrogen flames are practically invisible.
It doesn't take much "conventional" fuel as an adulterant to render the flame visible. The article states that the fire is "sustained in part by hydrogen" (emphasis mine).
It should however be taken into account that, although hydrogen itself doesn't contribute any CO2 to the emissions when burned, its production methods very well might be less than environmentally friendly in this regard.