I have been calculating FTEs for projects with shift work based on the 8 hour day and 40 hour work week. So, for example, if a project has three 9-hr shifts per day with 10 people per shift at 7 days a week, the FTE would be:
(10 people X 3 shifts X 9 hours X 7 days) / 40 hours = 47.25 FTE (48 FTE).

However, I have been questioning this becuase that 48 FTE calcuation is carried through to SSc4.2 for the shower calc and the WEp1 for the water usage calc. It seems that using the 40 hour base work week comparison unnecessarily inflates or double-counts workers by condensing 7 days of working to 5 days. For example, in the water usage calculation, you input annual days of operation for each Fixture Group. This will inflate the water usage because one should input 365 days of operation for the Fixture Group(as opposed to 260 for a typical 5 day week).

The SSc4.2 shower calc would seem to be inflated as well, although the weekend workers aren't double-counted like they are in the WEp1 form. I assume the shower calc is suppose to accommodate a typcial work day, but there will never be 48 people working on a typcial day at the facility.

So, I guess my question is, would it be more appropriate for projects with unusual shift work to look at typical 24 hr day, rather than a 40 hour work week? Thus the FTE would be:
(10 people X 3 shifts X 9 hours) / 8 hours = 33.75 FTE (34 FTE).

Any thoughts?