On January 27, 1967, the Apollo 1 spacecraft was being tested on its launch pad in Florida. All three men – Grissom, White, and Chaffee – were inside. The hatch was closed and the spacecraft was "pressurized" – meaning that there was more air inside than normal, which puts more pressure on everything inside. They needed to do this to make sure that the spacecraft was safe to fly in space. But rather than using normal air, the spacecraft was pressurized with pure oxygen.