3.25.5. Closed operation cabin: Where the worker is isolated from the source of the emission of dust from the materials presumed to contain or containing crystalline silica by the use of a closed operation cabin of a mobile machine, the cabin must have the following characteristics:(a) the air intake in the cabin must be filtered by a high-efficiency filter;
(b) positive pressure must be maintained;
(c) a heating and air-conditioning system must be included;
(d) the door and window joints must be kept in good condition to ensure they are sealed.