Jim,
My experience is with a plant of between a thousand and fifteen hundred people. I covered that comfortably with teams of relatively inexperienced auditors - 5 auditors per team, 4 times per year. Sometimes I joined in myself. I expected 4 hours actual time on the floor, from each auditor - I wanted them to complete the whole thing, report and all, in less that one day, to limit impact on their usual jobs.
So that makes a total of 4x5x4 hours = 80 hours. Say 100 for comfort and double it to include the report and add a bit more to cover time spent arranging with the guide and attending closing meetings and reviews.
So that's about it but, in fact, it was never the number of auditing hours I thought the job needed that dictated the time spent. The greater limitations were; 1) How much auditing the system could take before it became too much of a drag on the time and the patience of the auditees. 2) How many audits and auditors could I comfortably manage. I found that one a quarter was enough and to try to get teams together of more than about 5 did not provide returns for the effort involved. In fact (and Marc will agree with this, I've no doubt) I always said that it would have been easier and quicker for me to do the whole job myself, and the results would have been much better as well. This loses out on the gains made as auditors learn more about their own organisation but whether this is often an appreciated and used spin-off is doubtful.
Having said all that, though. The fact is that any reasonable amount of time and any old audit is probably good enough. The quality of the response is far and away more important than the quality of the audit.
rgds, John C
