How is Hathcock injured while patrolling in an Amtrac as noted in the biography, Marine Sniper?

While riding in an Amtrac on patrol in Vietnam; the Amtrac hits a large road mine during an ambush and catches on fire. Hathcock, engulfed in flames, remains aboard the vehicle and throws other unconscious Marines to safety. The valorous action saves lives but covers Hathcock in extensive and life-threatening burns.