The plugs-out test began on the morning of January 27, 1967, and immediately was plagued with problems. First the crew noticed a strange odor in their spacesuits, which delayed the sealing of the hatch. Then, communications problems frustrated the astronauts and forced a hold in the simulated countdown. During this hold, an electrical fire began in the cabin, and spread quickly in the high pressure, 100% oxygen atmosphere. Pressure rose high enough from the fire that the cabin burst and the fire erupted onto the pad area, frustrating attempts to rescue the crew. The astronauts were asphyxiated before the hatch could be opened.