Before each test and while the barrel is vertical and the burner is well away from the specimen,
the gas flame is to be checked to make certain that its overall height is 125±10 mm or 4-7/8 inches and
that the blue inner cone is 40 ±2 mm or 1-9/16 inches high, as established during calibration. A flame that
changes from blue to luminous without any change of the settings is an indication that the fuel-gas content
of the cylinder is exhausted and that the denser depletion-indicator material (propane, for example), which
some suppliers add to their cylinders, is being burned instead. In this case, the cylinder is to be labeled
as empty and then returned for refilling. Where the overall flame is blue and the height of the blue inner
cone is other than 40 ±2 mm or 1-9/16 inches without any change of the settings, the contents of the
cylinder likely are at low pressure. A gas-supply gauge pressure of 10 – 20 lbf/in2 or 69 – 138 kPa or 690
– 1380 mbar or 700 – 1400 gf/cm2 has been found to be adequate to maintain the required flame. A
cylinder shall not be used when this range of pressure is no longer sustainable at room temperature.