This paper is based on findings resulting from ASHRAE Research Project RP-1583.

For further development of refrigerant safety standards, burning velocity(Su)measurements of R-32/air and R-32/134a/air flames were carried out by the vertical-tube method with a 40mm (1.6in.) diameter tube, and the precision and measurable lower limit of the test method were investigated. To evaluate the precision of the test method, we obtained the ideal (buoyancy-free and with no conductive heat loss to the wall) burning velocities of these refrigerants by the spherical-vessel method in microgravity.