The Role Weather Played In An Apollo 13 Fire At The Launch Pad

You are probably aware of the explosion aboard Apollo 13 which occurred when astronauts performed a routine cryo-stir of the slush of liquid oxygen inside tank number two .  Exposed fan wires inside the tank caught fire in the pure oxygen environment, and the resulting explosion crippled the spacecraft.

But did you know there was another fire, set off by a weather event, involving a lot more oxygen and  much larger tank before the mission even got off the ground.

Early on the morning of March 25, 1970 security guards drove to the perimeter gate at Launch Complex 39-A to clear personnel from the area so that the day’s Countdown Demonstration Test could begin   Five minutes later their three cars were in flames.

Any rocket which uses fuels at cryogenic temperatures must be chilled down first.  The tanks aboard the Saturn V as well as the pumps, valves and even pipelines between the rocket and the giant spherical tanks containing the liquid oxygen (LOX) are cooled by pumping about 25,000 gallons of LOX through the system. Once the system has reached the proper operating temperature, about 11,000 gallons of LOX is drained off into 40 foot wide, 5 foot deep drainage ditch next to the pad.  This may seem wasteful but it ensure that good quality LOX fills the rocket’s fuel tanks and greatly reduces boil-off during the fueling procedure.

Normally the waste LOX harmlessly boils off into gaseous oxygen and mixes with the oceanside breezes at the pad. But not that day.

Cape Canaveral was experiencing a temperature inversion and dead calm wind conditions.  The LOX boiled off as expected but developed a dense, oxygen rich fog which spilled across the pad. NASA’s incident report estimate the cloud formed could cover 20 acres at a depth of 4 feet with oxygen concentrations up to 100% in the 5 acres immediately around the pad.

When one of the guards returned to his car and started it, flames shot from under the hood. The other two cars bust into flames as well.  As the security guards ran for cover, technicians rushed to drain remaining LOX from the lines, now just 10-15 feet from burning grass.

In the end there were no injuries and damage was limited to the three destroyed security vehicles.  According to a firefighter on the scene, the first vehicle had melted “absolutely flat”, on the second “everything from the firewall forward was pretty much gone” and the third experienced an engine fire but was put out quickly by emergency personal.

The guards never parked their cars there again.

Elsewhere in the sky, look for Venus about 11 degrees from the new moon in the predawn sky and Mercury and the moon just 7 degrees apart after midnight later this week.

Category: ALL POSTS, Spacey Stuff