[labnetwork] ambient gas detection for bulkheaded tools

[Mac Hathaway]

Hi Iulian,

At Harvard CNS, we monitor for toxics about 6 inches in from the back 
wall, on the cleanroom side, adjacent to the tool in question, to pick 
up ambient leaks in the "working space".  We also monitor "exhausted 
enclosures", typically the "gas box" where the VCR connected gases mate 
to the shut-off valves and MFCs at the back of the system.  As fittings 
are the most likely leak points, these are generally all within the 
enclosed and exhausted space inside the system, and represent a 
different level of risk compared to ambient leaks.  Thus, these 
monitoring points generate a local evacuation (cleanroom only), while 
ambient leaks are generate a building-wide evacuation.

The placement for the ambient detection points was based on where the 
technician would be (the "breathing space"), where the leak could come 
from (open chamber being considered most likely), and where the 
monitoring tubes won't be too much in the way.  We used swagelok 
bulk-head fittings mounted to the wall, with the plastic sample tubing 
(for our remotely located sensors) sticking out through the slightly 
larger diameter stainless bulkhead tubing.  Looks tidy, and supports and 
protects the tubing reasonably well.

We debated locating sampling points inside the bay, just outside the 
gratings at the base of the wall, and even directly below the wall in 
the room outflow, and chose our current configuration as the best 
compromise between response time (closer to source, less dilution), and 
most comprehensive coverage (further from source allows gases to diffuse 
sideways, so one sensor could see more "area" but concentrations would 
be lower).


Mac Hathaway
Harvard CNS




On 6/19/2013 12:53 PM, Iulian Codreanu wrote:
> Dear Colleagues,
>
> I am trying to figure out how the handle the detection of hazardous
> gases in the ambient when part of the tool is in the chase and part in
> the bay.  The connection between the tool and the line(s) carrying the
> gas(es) would be in the chase so it would make sense to monitor that
> area.  What are your thoughts on providing detectors on the bay side of
> the wall as well?
>
> Thank you very much for your help.
>
> Iulian
>