<prompt> In frost bite, skin becomes hard black in about :3 days7 days2 weeks4-6 weeks  <response>: C i.e. 2 weeks Trench immersion foot results from prolonged exposure to severe cold 5 -8degc of dampness. Frost bite occurs dt exposure to greater extremes of cold -2.5degc, develops more rapidly, may affect other pas such as nose, ears. Skin becomes hard black in 2 weeksQ after initial blanching paleness erythema edema bisters. 