The Bomb: "It's the End of the World" and "As We Know It"
In the second disaster episode of season two, a patient is brought into the ER with unexploded ammunition in his chest, and the bomb squad is brought in. Fresh off a premonition that she's going to die that day, Meredith winds up placing her hand inside the patient's open wound to keep him from bleeding out while the rest of the floor is cleared of personnel.
Things ultimately turn out all right for Meredith and the staff of Seattle Grace, but not so well for Dylan the Bomb Squad Guy (poor Kyle Chandler), who disintegrates into pink mist when the bomb goes off in his hands. Although he is only in two episodes, the proximity of his death to Meredith has lasting repercussions on her mental health, with the character even returning as a hallucination in a later season while Meredith hovers on the brink of death.