In early 1943, he was severely injured while working on homemade bombs for an underground sabotage operation when one of them accidentally exploded in the basement of his house. He lost sight in both eyes and faced the serious threat of hand-amputation. After his mother's intervention and the help of her fellow physicians, his eyes recovered fully and the hand was saved, but he never regained total control over it. After the recovery, Karpiński resumed his activities in the Home Army.