A rig was in the middle of an operation when it suddenly tipped over. There was no sudden noise, no gust of wind to cause the tipover. Although one of the racking board guylines was not connected, our analysis showed that this was not a major factor in the tip over. So what happened?
As it was winter and the temperature was below freezing, the crew was using steam continuously on the wellhead and blowout preventer to keep them from freezing. This had melted the ground underneath the rig and around the wellhead. This allowed water to accumulate under the rig matting over time, causing a loss of support underneath the rig, which in turn caused the rig to suddenly and unexpectedly tip over. Sadly, this case resulted in the loss of life of a crew member, who was unable to escape from the falling rig in time.