I worked a contract where we were living on site. They had a bar and sold beer to personnel so obviously drinking was okay. But there was a rule that you absolutely could not be intoxicated on site. I never got official clarification but my crew lead explained it basically means be prepared to pass a breathalyzer on-shift but off-hours you can get trashed you just had to keep it together. Getting a call at 3am when you're 12 shots deep to deal with emergent issues is a bit of a challenge. Not to stereotype but I think I was particularly lucky on that call that the personnel were from the Irish business unit. Some of the other personnel were boy scout-ish but these guys seemed to understand the deal.