I took the Class 1 Facility Operators Exam 17 years ago at an H&R Block Tax office in DC.   It was an open book exam at that time.  However, I would never have been able to complete the test if I had to rely on the book to look up each answer.  I believe there were three questions that I had to look up in the book to provide the exact answer, but it was only my familiarity with the regulations that allowed me to find the information quickly enough to complete the test in the time allotted.  I'd recommend a closed book exam.