Probably the FIAC, but they probably all are alike anyway.
As to pressure testing tanks the standard is to use water and a hydraulic pump, and this will be typically to 1.25 times the rated maximum pressure of the tank. The only exceptions to this are for oxygen systems, where the test medium is pure methanol or ethanol, so as not to contaminate the inner tank wall with corrosion, as this will act as a catalyst when pressurised with oxygen. Iron burns quite well in pure oxygen, you really do not want to start this though inside a tank with high pressure. one reason a lot of oxygen equipment is made in stainless steeld, pure nickel or aluminium, as all of these form a hard oxide layer on the surface, passivating it.
Of course if you want a nasty gas try fluorine, as literally everything burns in it, including things that you would normally consider non combustible, like asbestos, PTFE, sapphire, concrete, brick, rock. The only reason you can store it and use it in process units is that slowly introducing it into a system, which is only made from pure nickel, allows the formation of a thin coat of nickel fluoride on all exposed surfaces, which is able to withstand further fluoridation and protect the underlying metal. If this wears away too fast you get a reaction that is best viewed from a distance, and it finishes typically with a large very hot hole in the ground when the fluorine finally all has reacted with what used to be your plant and property.