The need for fast and simultaneous detection of multiple combustion-related chemical species in various industrial environments has motivated the use of comb-based spectroscopic techniques in these applications. Dual comb spectroscopy has been employed to simultaneously measure CO2 and H2O concentrations in a gas turbine exhaust with 1% precision [1], and cavity-enhanced optical frequency comb Fourier transform spectroscopy has been used to detect H2O and OH radical in a flame [2,3]. However, the time resolution of these measurements has so far been of the order of seconds. Here, we present a cavity-enhanced continuous-filtering Vernier spectrometer (CF-VS) that allows detection of H2O and OH in a flame with a time resolution of 25 ms.