The Apollo 13 mishap was caused by an explosion in oxygen tank #2 in the service module.

The O2 tanks had been redesigned to use 65V instead of 28V, but the heater thermostatic switches got overlooked.

During ground testing, the switches malfunctioned causing temp to rise and damage the teflon insulation on the wires to the fans.

On April 13, the fans were turned on for a "cryo-stir". The fan wires shorted, the teflon insulation caught fire, the O2 tank exploded.

https://nssdc.gsfc.nasa.gov/planetary/lunar/ap13acc.html
2/n

There is an interesting website that has a detailed real-time look at every moment of the Apollo 13 mission, with audio track from every mission control channel.

The malfunction sequence starts at 55:55:19.

https://apolloinrealtime.org/13/?t=055:54:59

Apollo 11 and 17 at https://apolloinrealtime.org/
3/n

Apollo in Real Time

A real-time interactive journey through the Apollo missions. Relive every moment as it occurred.

^{Apollo in Real Time}

This famous jerry-rigged "mailbox" was used to scrub the CO2 in the the Apollo 13 lunar module that was the lifeboat for the 3 astronauts.

The contraption solved the problem of fitting the lithium hydroxide cylindrical shaped scrubbers of the lunar module with the cubic shaped ones stored in the command module.

https://www.nasa.gov/history/afj/ap13fj/15day4-mailbox.html
4/n