Class B Operating Room

[emalsyd]

I need to design a Class B Operation Room. Supposed to have 20 ACH with 4 outdoor ACH, no recirculating room unit. I'm assuming by no recirculating room unit the unit needs to be 100% outdoor air. The 20 ACH with 4 OACH is throwing me off. If I'm 100% outdoor air wouldn't my outdoor ACH by the same as my supply air ACH?

 

[urgross]

If you have ASHRAE 170 available, you may want to look at that. You'll have 16 ACH of HEPA-ed air.

 

[dbill74]

Not necessarily. What you will need is a system capable of providing 20 ACH, of which 20% is OA (the 20 OACH). Per NFPA 99 the air in the OR cannot be circulated into other parts of the facility and must be exhausted. What is allowed is using recirculated air from other spaces in the facility into the OR, e.g. offices and corridors.

Similar to what you would do in a restroom space, only with laminar flow diffusers over the patient bed and sidewall return grilles near the floor.

 

[EnergyProfessional]

You really should read up on all the applicable health care codes and rules. there are many areas where you can use the re-circulation of chilled beams for that ACH requirement. but i doubt operation rooms are part of that. You also need to maintain the proper pressures to each space.

 

[tys90]

dbill74 - can you point out the section that refers to OR air not allowed to be recirculated?

 

[urgross]

I definitely would like to see that also. I just read through the NFPA 99-2015 and could not find it. I could point out guidance documents for class B and class C where the return grilles should be located in reference to each other and AFF requiremets.

 

[ZDR1985]

I did not find it also in NFPA 99 2015.

ASHRAE Application Handbook Chapter 7 (Healthcare Facilities) requires minimum 25 ACH and 5 OACH for operating rooms. No re-circulation within room, but does not say all exhaust air must be thrown outside.

 

[emalsyd]

I just downloaded Ashrae 170. This is what I found.
Table 7-1. Classes B&C operating rooms.
Positive pressure,
Min OA changes 4
Min total ACH 20
All room air exhausted outdoors N/R? Note J. I'm assuming that means not required.
Air recirculated by means of room units No
RH 20-60%

Note J for the room exhausted air: In some areas with potential contamination or odor problems, exhaust air shall be discharged directly to the outdoors and not recirculated to other areas. Individual circumstances may require special consideration for air exhausted to the outdoors, for example, intensive care units in which patients with pulmonary infection are treated and rooms for burn patients.

The area I'm looking at is rather small with an adjacent recovery room and soiled linen closet. I'm thinking of going with and erv unit to handle the exhaust and fresh air requirements. Plus also handles the MERV7 pre-filter requiement.

 

[dbill74]

NFPA 99 - 2005 section 6.4.1.3, also E.3.5.2 (Look up "ventilation" in the index.)
Rereading these sections again, looks like I have to correct myself and say NFPA does allow a percentage to be recirculated since 6.4.1.3 is referring to smoke originating within the OR.
I'm sure there is a newer version of the code available, but the 2005 version is what I have on hand. It would surprise me if things have changed drastically.
Don't be afraid to ask your AHJ for their interpretation, they are the one's that will be approving your design.

 

[urgross]

The 2015 NFPA 99 instructs the reader to refer to ASHRAE 170.

I'm not sure how retrun air would be treated differently than exfiltration air used to keep the OR relative positiv, even under the older codes. The OR's use typically 15% exfiltration air going to the clean core, which then uses exfiltration to stay relative positive to adjoining areas.