Cleanroom positive pressure

To All Valid

Can you tell us more about Air Flow Parallelism Test

Regards

A.Aziz
Al Pharao Air Data

This problem may either be resolved by now, or else accepted “as is”.
Some points to consider:

  1. the 0.5 Pa value is absolutely too high; refer to the lower values suggested in the string.
  2. “Positive Pressure” refers to the pressure in the room being higher “relative” to the pressure in the adjacent room(s). This has been correctly suggested by some in the string, where the descriptive phrase being used was “cascade”. This means that your Target room should have a higher pressure relative to the room(s) next to it. Several methods have been mentioned on how to do this, while other methods mentioned pertain more to maintenance applied troubleshooting; not performance validation.
  3. “Positive Pressure” does not refer to the INCOMING air being higher than the OUTGOING air. This refers to “System Pressure Drop”. The general way Positive Pressure is achieved is for the Target room to have a higher air changeover per hour (ACH) than its adjacent rooms. So its air handling unit’s flow rate (X cfm) divided by the room’s volume (Ft3) gives the number of times the air changes over per hour.
    ACH = X (ft3/min) / V (Ft3) * 60 (min/hour)

So cascade would look like this:

ACHlab > ACHgowning > ACHhallway

NOTE: Incoming = Exhaust - Leaks;
if using Incoming > Exhaust & Leaks, then the room would continue to build up pressure to intolerable and dangerous levels; this is what one commentor meant when he stated “the system will balance itself”.

  1. If you have leaks, then that is normal, and should be expected. The important thing is this: is the leakage at those areas in the Target room egressing, or ingressing? You want it to be egressing (exiting). In other words, if it were ingressing, then particulates/contaminants would be flowing from the adjacent room (like the gowning room) into the lab. This is precisely what “Positive Pressure” prevents (or minimizes).

Cleanroom pressures are actually measured by taking incosideration with adjescent room pressures.

If you look the EU guidance:

Pressure differential between rooms of different classes should be 10–15 Pa, and 12.5 Pa between a classified and nonclassified room.

The most widely accepted pressure differential for achieving containment between two adjacent zones is 15 Pa, but pressure differentials of between 5 Pa and 20 Pa may be acceptable. Where the design pressure differential is too low and tolerances are at opposite extremities, a flow reversal can take place. For example, where a control tolerance of ± 3 Pa is specifi ed, the implications of the upper and lower tolerances on containment
should be evaluated.
The pressure differential between adjacent rooms could be considered a critical parameter, depending on the outcome of risk analysis. The limits for the pressure differential between adjacent areas should be such that there is no risk of overlap, e.g. 5 Pa to 15 Pa in one room and 15 Pa to 30 Pa in an adjacent room, resulting in no pressure cascade, if the fi rst room is at the maximum tolerance and the second room is at the minimum tolerance.

[quote=DURGA PRASAD]Cleanroom pressures are actually measured by taking incosideration with adjescent room pressures.

If you look the EU guidance:

Pressure differential between rooms of different classes should be 10–15 Pa, and 12.5 Pa between a classified and nonclassified room.[/quote]

Mr. Shahnawaz,

Thanks for sharing & I do agree that the system should not be maintained at Lower & upper cascade range of pressure in adjescent rooms.

In addition to this few facts:

  1. Minimum pressure must be maintained in adjuscent rooms to keep the cleanliness level maintained.
  2. This minimum pressure either with respect to room or with respect to ATM.
  3. Air pressure & door directions should be taken in consideration while designing the pressure philo…

Opinions…

Happy Reading !

[quote=vijaypedineni]Mr. Shanwaz,

I have a doubt reg. differential pressures,
Pl correct my statement, clean room differential pressures should be individual and should be compared with atmospheric pressure and not with the adjacent lower class. [/quote]

Dear Mr Vijay,
No, differentail pressure should be consider with adjacent area and also consider the pressure cascading from process core (clean area) to transition zone, then to Ancillary area and in the end outdoor environment.
I hope it will be cleared your query and doubts.
Regards,
Dr. Shahnawaz Sajid