Friso94

Answer: Other answer is not entirely correct. The O2 tank was dropped in the North American factory, but they were unable to find any damage so they installed it on the Apollo 13 SM. 2 years later the spacecraft was sitting on the pad at Kennedy and they did the "plugs out test" with the spacecraft fully fuelled and running on internal systems. After the test was completed engineers tried to drain the tank and found they couldn't, the drain tube had been damaged when it was dropped. In order to empty the tank, they decided to run the heaters all night to boil the LOX off. This introduced the second problem: The spacecraft was engineered to run on 65 volts but the tank heater and fan were engineered to run on 28 volts. NASA changed the spec and it didn't find it's way to the sub-sub-contractor. NASA->North American->Tank Fabricator->Sensor manufacturer. With the heater running all night at 3 times the voltage it effectively cooked the elements, burning off insulation and such. When they ran the electronics inside the tank, it exposed bare wire inside the LOX to electrical current. Two of those bare wires shorted causing the explosion.

Answer: The oxygen tank had been used previously on the Apollo 10 mission, but tests revealed a fault, so it was taken out. For Apollo 13, that tank was reused after refurbishment, but one important thing that had changed was the voltage and amperage running through it to keep the oxygen warm; it was doubled for the Apollo 13. That melted through the isolation material, causing a short, which caused the tank to explode.

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