Section 43.52. Air pressure and hours of labor

(a) Less than 21 pounds. When the air pressure in any compartment, caisson, tunnel or place in which men are employed is greater than normal and less than 21 pounds per square inch, no employe shall be permitted to work or remain there more than 8 hours in any 24 hours and shall be permitted to work under such air pressure only if he shall, during the 8 hours, return to the open air for an interval of at least 30-consecutive minutes and the employer shall provide for the interval.

(b) Less than 30 pounds. When the air pressure in any compartment, caisson, tunnel or place in which men are employed is 21 pounds or more and less than 30 pounds per square inch, no employe shall be permitted to work or remain there more than 6 hours in any 24 hours, the 6 hours to be divided into two periods of 3 hours each, with an interval of at least 1 hour between the periods.

(c) Less than 35 pounds. When the air pressure in any compartment, caisson, tunnel or place is 30 pounds or more and less than 35 pounds per square inch, no employe shall be permitted to work or remain more than 4 hours in any 24 hours, the 4 hours to be divided into two periods of 2 hours each, with an interval of at least 2 hours between the periods.

(d) Less than 40 pounds. When the air pressure in any such compartment, caisson, tunnel or place is 35 pounds or more and less than 40 pounds per square inch, no employe shall be permitted to work or remain there more than 3 hours in any 24 hours, the 3 hours to be divided into periods of not more than 1 1/2 hours each, with an interval of at least 3 hours between the periods.

(e) Less than 45 pounds. When the air pressure in any compartment, caisson, tunnel or place is 40 pounds or more and less than 45 pounds per square inch no employe shall be permitted to work or remain there more than 2 hours in any 24 hours, the 2 hours to be divided into periods of not more than one hour each, with an interval of at least 4 hours between the periods.

(f) Less than 50 pounds. When the air pressure in any compartment, caisson, tunnel or place is 45 pounds or more and less than 50 pounds per square inch, no employe shall be permitted to work or remain there more than 90 minutes in any 24 hours, the 90 minutes to be divided into two periods of 45 minutes each, with an interval of not less than 5 hours between the periods.

(g) Time limit. The limits of hours specified in this section shall apply according to the maximum pressure attained at any time during the period when men are working.