Thomas Edison unintentionally caused the death of his assistant, Clarence Madison Dally, through radiation poisoning which caused cancer. Edison realized his X-ray experiments had poisoned Dally and stopped his research on X-rays after Dally’s death, saying, "I am afraid of them."

Thomas Edison unintentionally caused the death of his assistant, Clarence Madison Dally, through radiation poisoning which caused cancer. Edison realized his X-ray experiments had poisoned Dally and stopped his research on X-rays after Dally’s death, saying, "I am afraid of them."