Intrinsic cellular instabilities of hydrogen laminar outwardly propagating spherical flames

•Hydrogen-air flames were tested in a constant volume combustion bomb.•The onset of celluar instabilities were identified and analyzed.•Effects of equivalence ratio, initial temperature and pressure were studied.•Correlations of Pecl and Kcl, as a function of Mab have been developed.•Outcomes are useful for estimating the severity of large-scale hydrogen explosion.