[labnetwork] cleanroom occupancy ratings

[John Shott]

Iulian:

Just to add slightly to this discussion.  I also agree that going H-5 is 
the way to go.  As Mary pointed out, our facility (built in 1985) is a 
B-occupancy cleanroom with outboard H occupancy gas bunkers and chemical 
storage rooms.  While that is a lot better than a full B-occupancy, I 
believe that the code is not clear on how you "count" chemical volumes 
that pass from one occupancy to another.  I believe that it becomes a 
matter of what your AHJ will agree to.  In our case, I believe that we 
ended up with a reasonable outcome: we count the volume of gas that is 
downstream of the TGO-controlled shutoff valve in the bunker as the 
volume of gas that is counted as a part of the chemical inventory in the 
B occupancy.  That is fair and reasonable ... but not all AHJs would 
come to that same ruling I fear.

Even with outboard H-occupancy gas bunkers, we do have a couple of gas 
cylinders within the B-occupancy.  In particular, we've got a 5 lb 
bottle of boron trichloride for our etchers because of it's low vapor 
pressure.  We are soon to have an 8 lb bottle of anhydrous hydrofluoric 
for a vapor HF oxide process.  Those things get us closer to our 
B-occupancy limits.  When we add the water reactives in the form of 
sulfuric acid and a number of the ALD organometalics and the pryophoric 
nature of some of the ALD organometalics we are getting close to 
B-occupancy limits in several areas.

To me, the greatest risk in having a B-occupancy today is trying to 
guess what might be in use or desired at some far distant point in 
time.  My guess is that most university facilities of this type will 
have an expected lifetime of at least 25 years.

When our facility opened in 1985, for example, while many of the gases 
and chemicals are still in use, we certainly didn't anticipate things 
like anhydrous HF, all of the ALD organometalics, etc.  Moreover, over 
time, it seems as if PELs tend to go down and hazard ratings go up.  If 
a handful of the ALD organometalics get re-classified as pyrophoric, for 
example, over the next few years, or something like anhydrous HF gets 
reclassified "highly toxic" instead of merely "toxic", we are suddenly 
in an operational bind ...

While I know that building an H-occupancy is more expensive than an 
equivalent B-rated facility, I believe that this will help avoid 
unpleasant surprises over the life of your facility.

Good luck,

John


On 1/2/2013 9:40 AM, Iulian Codreanu wrote:
> Dear Colleagues,
>
> Happy New Year and thank you for all the useful feedback you have 
> provided!
>
> Could you please tell me/us what the occupancy rating of your 
> cleanroom is?  I am trying to convince some folks that H-5 is better 
> suited for future research flexibility than B.
>
> Thank you very much.
>
> Iulian