Air Pressure Requirements for OR Suite

Q: I have a small 28 bed hospital with one OR suite. Within the OR suite are sterile rooms, a soiled room, and of course the Operating Room, etc. We are rebalancing the air flows for the entire floor which is all health care occupancy. I am aware that the rooms mentioned above, all have air pressure relationship requirements to adjacent areas per the Guidelines for Design & Construction of Hospitals and ASHRAE 170. However, some are questioning the need to have a positive air pressure relationship between the OR suite and other areas. That is, they measure the pressure from the OR suite door to other side which is the in-patient corridor. Is there any pressure relationship requirement in this location?

A: ASHRAE Standard 170: Ventilation of Health Care Facilities section 7.1.a.1 states that design of the ventilation system shall provide air movement that is generally from clean to less clean areas. Since surgery departments may or may not be suites, the ASHRAE 170 ventilation Table 7-1 in the FGI Guidelines does not address that. You are correct that the actual operating room has to have a positive air pressure relationship to its surrounding areas. But in addition,  sterile storage areas should have a positive pressure relationship to all adjacent areas except ORs and restricted areas within a surgery suite should have a positive pressure relationship to all adjacent areas except ORs and sterile storage areas.