42 CFR §84.53

1. (a)Respirators described in subparts H through L of this part shall be classified, where applicable, as approved for use during the following prescribed service times:
   1. (1)Four hours;
   2. (2)Three hours;
   3. (3)Two hours;
   4. (4)One hour;
   5. (5)Forty-five minutes;
   6. (6)Thirty minutes;
   7. (7)Fifteen minutes;
   8. (8)Ten minutes;
   9. (9)Five minutes; or
   10. (10)Three minutes.
2. (b)Other service times may be prescribed by the Institute.