[labnetwork] question to cleanroom colleagues: distributed vs. manifolded gases...

[John Shott]

Ian:

Like some of the others, we tend to have tapped lines for inerts/freons 
and VMBs for some (but not all) of our hazardous/corrosive/toxic lines.

In addition to the comments of others, let me add a couple of additional 
thoughts relative to use of VMPs/VMBs for hazardous/corrosive gases.

There seems to be a broader range of configuration options in VMBs than 
there are in cabinets themselves.  There are the "Cadillac" fully 
automated systems ... nice, but pricey.  We have fully manual VMBs.  
Even there, however, there are options.  We have nitrogen purge 
capability for each line in our 4- or 8-stick boxes, but no venturi.  
Our assumption is that all tools connect downstream of a VMB will be 
able to pump out the line, but it's nice to be able to backfill with 
N2/He for a manual cycle-purge.  My guess is that others will have 
different configurations and reasons for using them.

In addition to the cost of the VMB/VMP .... particularly for hazardous 
gases ... you should think about whether this will require additional 
gas detectors, whether you'll also need to be adding extra 
panels/cylinders for purge of your VMBs etc.    While I like VMBs for 
things like BCl3 and chlorine, these additional items increase the 
cost.  Of course, an all welded BCl3 or Cl2 system is problematic if you 
ever want/need to make changes. I've yet to find a welder willing to 
certify a weld on a system that has been used for these gases.  Most 
jurisdictions will require all non-welded connections to most 
toxic/corrosive gases be in an exhausted (and in some cases monitored) 
enclosure.  The incremental cost of VMPs/VMBs also depends one the 
distance between the gas cabinet, a potential VMB, and the tools.  In 
our case where the distance between the gas bunker is large (we 
typically have 400-500 feet of line between gas cabinet and tool/VMB) 
and the distance between VMB and tool is more like 30-50 feet, the VMB 
isn't such a large incremental expense.

Good luck,

John