<prompt> In frostbite, skin becomes hard black in about -3 days7 days2 weeks4-6 weeks  <response>: The localized effects of cold are frost-bite, trench foot, and immersion foot.Trench foot and immersion foot wet cold result due to prolonged exposure to severe cold 5-8 C and dampness. Blister formation with ultceration and localized dry gangrene occurs.Frostbite is infarction of peripheral digits with oedema, redness and later necrosis of tissue beyond a line of inflammatory demarcation. It occurs due to exposure to greater extremes -2.5 C of cold. Necrosis with blister formation and gangrene occur. Skin becomes hard and black in about two weeks. The sequence of events is:-Erythematous patches few hours Soft blisters 24 - 36 hoursHard and black 2 weeksDeep up to the none 1 month 