Walwyn Jackson, Leak Detection Service Supervisor
Walwyn.Jackson [at] inficon.com
It is a widespread misconception that the flammability of Hydrogen would make it impossible to benefit from its advantageous properties in leak testing. In fact, Hydrogen is only flammable in the concentration range 4% - 75% in air or oxygen, and can only detonate in the range 18% - 60% in air or oxygen.
By using pre-diluted Hydrogen, one can avoid the flammable concentration range altogether. Standard Hydrogen/Nitrogen mixtures are, for example, commonly used as shielding gases for welding purposes.
Hydrogen can therefore safely be employed for leak testing if used at the right concentration. A suitable concentration to use is the standard 5% Hydrogen / 95% Nitrogen mixture which is available in industrial grade from most gas suppliers. The price is only a fraction of the price for helium.
The 5% mixture is classified as non-flammable according to international
10156. This standard not only describes how flammability limits of gas
mixtures are to be determined, but also states that Hydrogen/Nitrogen mixtures
containing less than 5.5% Hydrogen are non-flammable, irrespective of how
this mixture, in turn, is mixed with air.