Quenching limits of hydrogen diffusion flames on small burners were observed. Four burner types,
with diameters as small as 8 m, were considered: pinhole burners, curved-wall pinhole burners, tube
burners, and leaky fittings. In terms of mass flow rate, hydrogen had a lower quenching limit and a higher
blowoff limit than either methane or propane. Hydrogen flames at their quenching limits were the weakest
flames recorded to date, with mass flow rates and heat release rates as low as 3.9 g/s and 0.46 W. The
quenching limits were generally independent of hole diameter and burner orientation, and generally
decreased with increased surface curvature. The quenching limit for a hydrogen flame at a 6 mm leaky
compression fitting was found to be 28 g/s. This limit was independent of supply pressure (up to 131
bar) and about an order of magnitude lower than the corresponding limits for methane and propane.