ANSI/ASHRAE Standard 15-2010 Section 8.11.5 suppliesa formula to determine the ventilation rate requirement forrefrigerating machinery rooms. The current formula suggeststhat the appropriate ventilation rate to flush a refrigerantduring a leak is proportional to the square root of the mass ofthe refrigerant in the room. A search for the historical roots ofthe basis of this approach indicates that this formula was likelydeveloped before 1930. A more rigorous and scientificallysound approach yields a technically defensible rationale forventilation requirements in refrigeration machinery rooms tomaintain safety. This paper examines recorded accidentscenarios to develop an appropriate leakage scenario and aventilation requirement that takes into account several importantparameters: the mass of the refrigerant, refrigerant properties,the volume of the room, the delay in detection, and therecommended concentration limit suggested for health andsafety purposes. After determining an appropriate, time-varyingemission rate, a mass balance equation is used to determinethe concentration of the refrigerant in the room. The refrigerantconcentration in the room is kept below the recommendedconcentration limit by adjusting the ventilation rate.