Review of methodology to set safety factors for A2L flammable refrigerant being adopted by product safety standards.

Many new lower GWP refrigerants are flammable under certain conditions. Flammability risk can be lowered by reducing the potential for forming a refrigerant/air mixture that can reach the lower flammability limit (LFL) in the event of a leak into a confined space. Product standards are setting safety factors from 4x (25% of LFL) to 1x (100% of LFL) for A2L flammable refrigerants. This large discrepancy in safety factor practices is being driven by different methodologies in understanding of refrigerant leaks from equipment. Unfortunately when a leak occurs, uniform mixing of the refrigerant with the air does not occur immediately. This can result in localized refrigerant peak concentration that exceed the LFL which requires a safety factors to be applied to account for noise factors. An additional complication is that noise factors can vary by product application. This paper will review the practices for setting the safety factors, understanding noise factors and resulting safety margins for safety factors ranging from 4x (25% of LFL) to 1x (100% of LFL).