The mission was to be Apollo's first crewed flight, and it was set to launch on February 21, 1967. A fire ripped through the command module, or CM, killing astronauts Virgil Grissom, Edward White, and Roger Chaffee. The cause of the fire has never been determined conclusively. Some witnesses reported seeing flames inside the spacecraft, while others said they saw nothing unusual before the accident. The astronauts died of asphyxiation due to lack of oxygen in their lungs. They were burned beyond recognition. The only way to identify them was by their dental records. Apollo 1 was the first manned spaceflight to fail during its opening mission. It was also the first time three people had died in a single spaceflight. This fact alone made the tragedy very memorable. Additionally, the fire that killed the astronauts occurred during a ground test of an emergency ventilation system used on later missions. This too makes the Apollo 1 disaster one to remember for years to come. Of the four men who went into orbit on Apollo 1, only Grissom and White survived. Chaffee, who was sitting in the command seat, died along with the crew cabin. He is now listed among those who have given their lives in space exploration. After Apollo 1, many changes were made to prevent similar accidents in future missions.