Use of an aqueous composition comprising (a) at least one strong oxidizing agent, (b) a color indicator system and (c) at least one thickening agent for detecting contamination of a surface with organic substances by means of visual inspection after planar application of the composition to the surface. The composition after application over the area is non-flowable for a predetermined time period due to the action of the thickening agent. The thickening agent is stable for the predetermined time period in the composition. Use of an aqueous composition comprising (a) at least one strong oxidizing agent, (b) a color indicator system and (c) at least one thickening agent for detecting contamination of a surface with organic substances by means of visual inspection after planar application of the composition to the surface. The composition after application over the area is non-flowable for a predetermined time period due to the action of the thickening agent. The thickening agent is stable for the predetermined
