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This paper compares the major concepts in ventilation requirements contained in American Petroleum Institute (API) RP 500/505 and International Electrotechnical Commission (IEC) 60079-10, specific to indoor lighter-than-air natural gas hazardous atmospheres. Engineering professionals rely on API 505 as the basis for area classifications. Previously, IEC and North American standards have been successfully adopted in the body of API 500/505 (79-10 Mod). However, the informative appendixes of both standards covering ventilation calculations are not entirely consistent. This paper presents case studies for ventilation/classification, and an attempt is made to harmonize ventilation calculations to offer further uniformity in global standards. This will be of interest to those involved with area classification activities, as the result may offer reduced mechanical ventilation demands, while maintaining equivalent levels of safety and reliability.