The Wilhelmsen Ships Service standard for Span-Gas:

1. For all hydro-carbon gases: 30% - 50% L.E.L (Lower Explosive Limit) in Air
2. For all hydrocarbons: 35% - 40% L.E.L. in Nitrogen
3. For Inert Gas Systems: 1 % - 19 % O2 in Nitrogen
4. For Controlled atmosphere: 5 % CO2 in Nitrogen

The standard LEL - value (Lower Explosive Limit) is 35 % which is suitable for allmost all types and versions of explosive meters.