×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Negative pressure in Room and air balance

Negative pressure in Room and air balance

Negative pressure in Room and air balance

(OP)
I have a doubt:

If a have a negative pressure in a room, does it suppose that i have a negative air change?

Because my extraction is bigger than my inyection of air to the room.  these is rigth or not?

I have to report my air changes in a pharma instalation and i have that doubt.

Please help me.

Sergio Avila

 

RE: Negative pressure in Room and air balance

Not right.  Even your doubt is doubtful.  Everything is relative.  

If you have a little negative pressure in a room, it is still positive to the general universe and likely to atmospheric pressure... and some other space closer to the supply fan.

Negative pressure can be obtained with any number of air changes - air changes can be had as long as there is air passing through a room.  Look at your air flow and calculate the air changes based on that data and the volume of the room.

RE: Negative pressure in Room and air balance

KiwiMace,

Biological production units maintain areas negative with respect to atmosphere, particularly when viruses or GMO are being handled.

Sergio,

You calculate ACPH based on supply flow rate and not net flow into the room. ACPH indicates how many times your room air is being refreshed (by filtration) to maintain the required particualte level.

RE: Negative pressure in Room and air balance

I would recommend reviewing USP 797 if you are doing pharma. Whether you have a positive or negative differential pressure, or both, would probably depend on that. For toxic compounding you would need a negative enclosure, such as a bio cabinet or other ISO 5, surrounded by a positive enclosure, generally ISO 7. Entry would be through a vestibule under negative relative differential pressure compared to the ISO 7, for personnel and material movement. The USP 797 has some simple figures with it to illustrate the relative pressure differential for compounding and toxic compounding.

If you are handling viruses, you would probably be in a BSL-2, 3 or 4, which is an entirely different requirement from the BMBL.

If positive, I count air changes by supply for the ISO ACH requirement, and look for a 0.05 IWG at balance by dampering the exhaust. For negative I go by ISO ACH requirement on the supply side, and damper back the exhuast at balance for the 0.05 IWG. A magnahelic on the wall before entry should be considered for operations. Differential flow indicates relative differential pressure. The amount of flow difference needed is reflective of the leakiness of the enclosure.

RE: Negative pressure in Room and air balance

OK quark, but the OP is still not right.

RE: Negative pressure in Room and air balance

Calculating an air exchange rate for any space is based on the higher of the flows (exhaust or supply).

RE: Negative pressure in Room and air balance

I am not sure about other industries but it is supply in Pharma. Excess return air, in case of negative pressures, is a result of leakage from other areas. This is considered to be untreated.

RE: Negative pressure in Room and air balance

Treated or untreated, sucking out air and re-injecting it is ACH101. Air is exchanged regardless of passing through whatever supply filter media is in place.
 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources