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Operating Room Pressures

Operating Room Pressures

Operating Room Pressures

Please be patient with me.  I'm a first timer and know nothing about your work.

I am an RN and acting OR Coordinator in a small OSC in Florida.  We have to maintain at least 15 air changes per hour in our ORs and they have to be at positive pressure to at least .01".  This is according to our industry specs I have read.  Temp and humidity are also a part of the equation.  We have a guy that comes in and checks these and other things.  I want unbiased advice, so here are my questions:

1.  He puts a big blue canvas thing up the the vents to read the airflow.  First, what is that and is that the best way to read the actual air flow/changes in the room.  It is reported to us in CFM and then converted by some program he uses into ACH (air changes per hour??)

2.  He has a rubber tube attached to a small device that is inserted under the door from the corridor, into the OR  That apparently gives him the pressure for the OR.  i'm assuming since he is outside the OR, it is comparing it to the pressure in the corriodor.  Is that the normal way of doing that?

3.  The ACH seem to fluctuate (sometimes a little and sometimes a lot) each time he comes.  Sometimes the pressure is above .01" according to his report.  But at other times, it is down to around .004" which means our OR is not compliant.  Why does this happen?  He has suggested that if the returns are too high, then it affects the pressure.  Looking back on the reports.  It does seem that when the returns are at about 60% of supply, the room is fine in respect to pressure.  But, when the returns get up to 80% of the supply the pressure seems to dip down.  Is it merely a result of the supply/return relationship?  Why do the return CFMs go up and down?

4.  There was one instance where he checked a soiled utility room that is supposed to be negative in respect to the OR corridor. There is a supply and an exhaust vent in the room.  At the time he checked it, there was more supply than there was exhaust.  This made the room positive he said, and I did see by a tissue test that the air was flowing into the corridor.  According to him, even though the supply was providing more than the 10 ACH needed for the space it also didn't have enough of the right ACH.  He said the ACH needed to be supported by the exhaust...not the supply.  Is this right??

I know this is long, but I really do need help here because I really do want to understand and make sure we're not just spending money on things we don't need.

Thanks for any help you can give!!!

RE: Operating Room Pressures

Hi Abby,

I have experience in just these situations -- I was director of engineering at a couple of large hospitals in my career, and I've also been on the controls contracting side.

It sounds to me like you have a good guy doing your testing. All standard tests, with appropriate answers in my opinion.

The return(exhaust?)/supply relationship in your OR should be stable -- 60% return sounds like the target (not unusual).  Supply needs to exceed return by an amount that makes up for cracks around the doors and static pressure changes in the ductwork.  The ORs I have dealt with had 100% outside air units, so there was no "return," only exhaust.  Your ACH and room pressure may fluctuate for a wide variety of reasons, but controls are probably at the heart of it.

Same with your soiled linen room -- exhaust has to exceed supply by a margin that keeps the negative pressure high enough.

Both can be controlled with a differential pressure transmitter if needed, but this is not always done.

Knowing nothing about your control system, I can't give a recommended answer for your situation (other than that it needs some tweaking). In most cases, the test and balance people need to coordinate with the building automation system (controls) people to determine what is causing the variation in pressure, and it usually is a simple matter of tuning controls to get it back to its original consistency.

Hang around for others' opinions, too.  There is a wealth of knowledge in this forum.   

Good on ya,

Goober Dave

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RE: Operating Room Pressures

I agree with the above post from GRW, your technician is doing an excellent job for your Facility. He is not hiding anything but giving you a "snapshot" image of your systems at the time he made the readings. These are dynamic systems that open and close acccording to programmed parameters. They can be adjusted in most cases with some software or hardware that you may already have installed. You can also have the tech advise you on differential pressure transmitters that will give you an instant readout and an alarm at the door if the system should go out of the Ashrae parameters. It is possible that you may need some upgrade to software and hardware and you should be open to that, but it does not seem likely as far as the data you have provided. From the descriptions you have given, you have a very consciences tech there. I am a Chief Engineer and instructor in healthcare. Good Luck. Your Facility is also lucky to have You, as your level of perception and care about your patients shows through your post.

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