In the emagram, the dry adiabats make an angle of about 45 degrees with the isobars, isotherms are vertical and isopleths of saturation mixing ratio are almost straight and vertical.
Hydrogen is easily ignited, as it is flammable over a wide range of concentrations in air, so that the test does not rely on having an exact mixing ratio.
The drawbacks are explosion hazard and high sensitivity of the deposition rate and morphology to the process parameters, such as mixing ratio, substrate temperature, etc.