This part of ISO 20492 specifies two methods of test for insulating glass units, including a determination of the gas leakage rate and a determination of gas concentration tolerances. The two methods designated as approach 1, which is intended for use in markets such as North America, and approach 2, which is intended for use in markets such as Europe.
GSO ISO 20492-3:2013 history
2013GSO ISO 20492-3:2013 Glass in buildings -- Insulating glass -- Part 3: Gas concentration and gas leakage