We have a nice big red button at security which is pressed by everyone entering site, be they a Visitor or Director. They have 1% chance of it going red, if it goes red they get tested by trained Managers. We also test off the back of a vehicle accident or if we believe someone has had a few (i.e. can smell it on them!) Anyone that tests positive is dealt with accordingly. It works well and has the backing of the Union and we tend to capture a wide range of people (including me) and its pretty fair.

In the oil & gas industry, its now done as a matter of course.

Working in a small community and where we operate a public service, we also test after accidents / incidents. This is primarily to protect employees against public accusations after the event "oh he is always drunk". To have a test immediately after the incident deflects this element of criticism. Again with union support.