Port-A-Potties. What is their user capacity?

[Paul Sandhu]

There is going to be a large industrial construction project starting in the near future in my town.  Yesterday 10 port-a-potties magically appeared next to the job site. 10 of them, all in a row.  The job site is 4 vacant city blocks.  Is there a certain number of the port-a-potties for the number of people expected to be working?  If so, what is the number of people per potty?  If it is not the number of people, is it the dependent of the size of the job site?  Or do you think the company doing the work just put an arbitrary number of the potties there?  The company follows OSHA standards fairly well.