In offshore rig ventilation design, attention is to be given to the vents inlet and outlet locations and airflow in order to minimize the possibility of cross contamination. Ventilation inlets are to be located in non-hazardous areas. Ventilation for hazardous areas is to be completely separate from that for non-hazardous areas.
Enclosed hazardous spaces are to be provided with ventilation so as to maintain them at a lower pressure than less hazardous zones. The arrangement of ventilation inlet and outlet openings in the space is to be such that the entire space is efficiently ventilated, giving special consideration to location of equipment which may release gas and to spaces where gas may accumulate. Enclosed hazardous spaces containing open active mud tanks are to be ventilated with high capacity mechanical venting systems capable of changing the air every two minutes.
The outlet air from Zone 1 and Zone 2 spaces is to be led in separate ducts to outdoor locations which in the absence of the considered outlet are of the same or lesser hazard than the ventilated space. The internal spaces of such ducts are the same Zone as the inlet space. Ventilation ducts for hazardous areas are to be at under pressure in relation to less hazardous areas and at overpressure in relation to more hazardous areas, when passing through such areas, and are to be rigidly constructed to avoid air leaks.
Ventilation inlets and outlets for non-hazardous spaces are to be located in non-hazardous areas. Where passing through hazardous areas, ducts are to have overpressure in relation to the hazardous area.
Courtesy of ISO standard