European Commission (EC) scientists have concluded there is "no evidence of a serious risk" for automakers using r1234yf refrigerant, despite Mercedes-Benz having deep misgivings concerning the coolant.

The issue has put the German manufacturer at loggerheads with the Commission and French authorities, which initially banned Mercedes from selling its A, B, CLA and SL models using the automaker's preferred r134a refrigerant, a decision subsequently overturned by Paris' highest Court.

Mercedes maintains the r1234yf coolant could present a fire hazard in certain conditions, although one manufacturer, Honeywell, points to its safety and vastly more environmentally-friendly emissions properties.

"A scientific review of the research regarding the safety aspects of the use of refrigerant r1234yf in Mobile Air Conditioning (MAC) systems, published by the EC, concludes there is no evidence of a serious risk in the use of this refrigerant in MAC systems under normal and foreseeable conditions of use," said a Commission statement.

"The review reinforces the conclusions by the German market surveillance authorities the KBA (Kraftfahrt Bundesamt), which stated there is no sufficient supporting evidence of a serious risk that would entail the intervention of the authorities."

The EC added the KBA testing procedures were conducted as a "confidence-building measure" it had proposed to Member States, with Brussels' own Joint Research Centre reviewing the methods.

"In practical terms this assessment reaffirms the position of the Commission the automotive manufacturers have the means to mitigate the inherent risks of the use of the refrigerant, which are known and have been studied," added the EC statement.

"The refrigerant is not the only fluid used in vehicles that is flammable or that may cause formation of dangerous emissions when burning.

"Automotive manufacturers, as part of their responsibility to provide for safe products, have found ways to mitigate these risks in a way that is consistent with a high level of protection for the safety and health of persons."

Mercedes previously told just-auto it was "at full throttle" developing CO2 air conditioning systems.

"We have our first prototype in testing since December," a Mercedes spokesman said. "These are vehicles from three different model ranges - we will expand our fleet of prototypes step by step."