Single-shot HCHO laser-induced fluorescence (LIF) imaging measurements in a tech.-scale turbulent flame were obtained using XeF excimer-laser excitation in the ~A1 A2-~X1 A1 transition at 353.2 nm. Measurements were carried out in a 150-kW natural-gas swirl burner where HCHO distribution fields have the potential, in combination with OH concn. fields, to visualize the heat-release distribution and therefore give an optimal visualization of flame-front positions. The extended areas where HCHO was detected in the swirl flame indicate the presence of low-temp. chem. in preheated gas pockets before ignition.