I know generally speaking, most of, if not all the big company's I worked for, when a ban is in place it usually is because of an incident. A knife for example may have stemmed from several people over the past slipped when cutting something and injured themselves where they were probably flown back to land for further treatment (stitches, etc..) I doubt insurance policy's are responsible, I have worked in many sensitive fields and we were allowed to carry knives until a government agency banned them due to a security threat. My current working environment is very effective with it's policy, they have no problem with knives under a certain length as long as it's kept hidden and used for the job. If you go against any of their safety policies, they and their insurance company will not pay a dime. This gives the employee a Hugh incentive to follow there safety guidelines because the bottom line is if you get hurt and you were not following there safety rules, then you will pay full medical costs. I love this policy and think it should be standard, there is nobody treating you like a child by watching over you every second, they treat you like adults and rely on your good judgment. The bad ones are weeded out very quickly.

In the case of the rig, if I had been on that rig, I would have a knife on me. I doubt they get searched going to and from that rig. It is up to the user to take the risks and if I'm in a position where my life may be in jeopardy if I don't have one, I will carry one or look for another job as well. Their are also loop holes in a lot of policies like carrying a knife, fork and spoon for your lunch. Many do not specify what kind of knife you have to have for cutting the steak you brought for lunch.