At hospitals, training for disasters put to test ← Related Article Visit The Boston Globe Share on Twitter Share on Facebook Comment on this Scroll to top of page John Tlumacki/Globe Staff Chaos ensued at the finish line of the Boston Marathon when two bombs exploded on Monday afternoon, injuring dozens and killing several. David L. Ryan/Globe Staff The day began as a beautiful, sun-filled, and joyful time as runners completed the 26.2-mile trek from Hopkinton to Boston. David L. Ryan/Globe Staff But the tenor of Marathon Day changed quickly when the first of two successive bombs exploded along Boylston Street just before 3 p.m. David L. Ryan/Globe Staff A short time later, the once-joyous finish line scene had become a crime scene under lockdown. John Tlumacki/Globe Staff The jolt of the first blast knocked this runner to the ground and prompted police to spring into action. John Tlumacki/Globe Staff Seconds later, another explosion rocked the street several blocks away from the finish line. John Tlumacki/Globe Staff To reach the injured, bystanders had to tear down a makeshift fence that had been built for the marathon. John Tlumacki/Globe Staff Police and marathon officials struggled to remove the barriers. John Tlumacki/Globe Staff The blast created a smoky haze that contributed to the confusion that reigned in the ensuing minutes. John Tlumacki/Globe Staff This man comforted one of the victims along the sidewalk. John Tlumacki/Globe Staff First responders sprang into action to help the injured people. John Tlumacki/Globe Staff A marathon official helped the runner who was thrown to the ground by the initial blast. John Tlumacki/Globe Staff The scene along the sidewalk near the bombing was gruesome. David L. Ryan/Globe Staff Wheelchairs that were on standby for runners who needed help at the finish line were put into use for those injured by the blasts. John Tlumacki/Globe Staff First responders wheeled away one of the injured on a stretcher. John Tlumacki/Globe Staff Another injured person was carried away by first responders. Bill Greene/Globe Staff Former Patriots offensive lineman Joe Andruzzi carried an injured woman away from the scene. John Tlumacki/Globe Staff This woman dropped to her kneels in reflection after the blasts. Bill Greene/Globe Staff The blasts were traumatic for many at the scene, and caused people to flee the area. Yoon S. Byun/Globe Staff Runners who had not yet finished the race were stopped on Commonwealth Avenue. John Tlumacki/Globe Staff The blasts blew out windows and left a trail of debris along Boylston Street. David L. Ryan/Globe Staff The blasts left an indelible image on the Boston Marathon, which will likely be forever changed by Monday's tragedy.