Comment submitted by Michael Schneider, BMW Group

Answer to the proposal for the EPA SNAP rule for R744 including a ceiling limit for CO2 of 4% at any time. 1. A corrosion leak of the evaporator always starts with a very small hole so that it takes several hours for the refrigerant to flow into the passenger compartment. Under operating conditions the air exchange rates through the vehicles are high enough (even in recirculation mode) that no critical concentrations can be achieved. So the only cases where an occupant could be exposed to a concentration above 4% are: - If somebody stays several hours in the vehicle without operating it (e.g. for sleeping) - If during an accident the very unlikely case happens that only the evaporator breaks (no other component of the refrigerant circuit especially in the engine bay is damaged) and the passenger compartment stays undamaged (no windows break and no other opening to the surrounding occurs) In both cases the typical effects of a CO2-concentration of 4% (dizziness, headaches, faster breathing rates …) would not cause any additional harm to the occupant, because: - The occupant is sleeping anyway (the highest CO2 concentrations occur in the lower part of the passenger compartment due to the fact that CO2 is heavier than air) - The accident that leads to the massive damages is so severe that the additional effect of the CO2 exposure is insignificant compared to the consequences of the accident itself So it can be concluded that the implementation of measures to prevent a CO2 concentration above 4% in all cases would not only be very complex but would also not improve the level of safety for the occupants. So the introduction of a ceiling limit for CO2 of 4% is not supported because it’s not necessary to assure the occupant’s physical integrity in the cases that can lead to a refrigerant leakage into the passenger compartment. The proposal for CO2 limits that have to be prevented in the vehicle are (confirmed by a SAE CRP): - A ceiling limit of 9% - A time weighted average of 5.5% over 5 minutes - A time weighted average of 4% over 30 minutes 2. The proposed use conditions for R744 should only apply when the ignition is on.