posted 09-20-2015 02:17 AM
The LOX used to fuel the Saturn V was stored in a 800,000 gallon insulated tank and transferred to the umbilical tower across a gap by an uninsulated pipe. Before the LOX actually used to fill the tanks of the rocket could be loaded, a long chill down process of this pipe, lines and launch vehicle had to be done using about 25,000 gallons of LOX. This, once it had done its job was allowed to drain into a ditch in a nearby swamp. Usually, it was not a problem as the LOX vapourised, mixed with the air and was blown away in the wind.
However, on the day in question a dead calm, an overcast sky and the prevailing temperature and humidity combined to prevent the LOX dispersing. Instead it just sat in the ditch creating a localised fog of pure oxygen vapour.
The police cars, having completed their sweep of the launch complex usually made their exit through a gate close by the LOX facility. On this day, as they drove to the gate and through the fog, the hot engines and grease in the pure oxygen caught fire.
Nobody knew at the time what was happening, but once the excitement had died down the CDDT continued without further incident.
The police never used that particular exit gate again.
On edit: Just to clarify the chill-down process. The oxygen involved was that used to chill down the LOX transfer pump. This was fed by gravity from the storage tank and allowed to escape through a 3 to 4 inch pipe that ran under the pad perimeter road and into the swamp. It was this oxygen that failed to disperse and which the cars ran into.
After the pump was chilled down they started the pump at low rpm and flowed LOX up the uninsulated transfer line into the S-1C first stage where it was vented off through the S-1C vent valve until the transfer line was chilled down and carrying good quality LOX to the Saturn V stages. They then started to fill the vehicle.