One of the worst tragedies in space exploration occurred on January 27, 1967. The Apollo 1 crew was performing a plugs-out test before the actual launch date when a fire broke out and engulfed the cockpit, burning all three astronauts alive. The launch pad personnel struggled to open the hatch, but a poor hatch design combined with pressure suction problems required 5 minutes to get it open.
The cause of the fire was determined only after an extensive investigation. The fire resulted from a spark from a short circuit underneath a seat in the command module. This resulted in the seat catching fire and, with the high amounts of oxygen, the fire spread quickly. As a result of the tragedy, changes were implemented in the command module design, including a new hatch design and removal of highly flammable materials.