Service time; classification.

(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) Four hours; (2) Three hours; (3) Two hours; (4) One hour; (5) Forty-five minutes; (6) Thirty minutes; (7) Fifteen minutes; (8) Ten minutes; (9) Five minutes; or (10) Three minutes. (b) Other service times may be prescribed by the Institute.