[labnetwork] Gas cabinet for F2 premix for excimer lasers?

[Dennis Grimard]

I could not agree more with Noah.

My take on this:


1.     Let’s say you have the bottle in a smallish room … say 10x10x10 or 1,000 CF.


2.     Let’s say you leak 1 CF … that is a dilution of 1,000X



3.    0.2 % F2 in whatever is 2,000 PPM …



4.    Assuming perfect and uniform dissipation throughout the room … the room concentration would be 2 ppm.



5.    That is 20X the PEL which is a legally enforceable exposure limit … independent of a non-binding CGA recommendation.



6.    At 2 ppm you would be right at the odor threshold … so you would have a poor warning property to the leak


Of course my logic could be wrong, my math could be wrong and the amount of the leak could be less … or more … you should verify for yourself.

Finally, if you did have a leak and the people were not able to detect the leak until they began to experience the effects of F2 exposure … what do you tell them?  The CGA P-20 pamphlet said it was ok?  As Noah says ... pitchforks might be the least of your worries.

Put it in the gas cabinet …. Or a vented enclosure with detection.  At the very, very, least, place a vent in the room with a detection point in the vent to actively sweep up (constantly sample) a possible leak that could occur.  I would smoke the room to make sure that any point in the room eventually ends up in that vent at some point in time.

D

Dennis S Grimard, Ph.D.
Associate Director of Operations

MIT.nano
School of Engineering
Massachusetts Institute of Technology
60 Vassar Street, Bldg 39-559
Cambridge, MA 02149

C:     (734) 368-7172
EM:  dgrimard at mit.edu<mailto:dgrimard at mit.edu>

On Mar 4, 2017, at 9:04 AM, Noah Clay <nclay at upenn.edu<mailto:nclay at upenn.edu>> wrote:

Hi Sandrine,

We have a 193nm excimer laser micromachining system in our cleanroom and went through a similar exercise.

We concluded that even though OSHA or NIOSH limits would indicate that a gas cabinet is unnecessary, that housing the ArF cylinders in an exhausted enclosure is a safer/better option.  Since the laser requires frequent purges/refills, placing the cylinder near the cabinet is a must - therefore, it needed to be placed in an adjacent service chase.  And so, we reasoned that:

1. Housing F2 gases directly in the recirc path (no gas cabinet) was not an option.

2. Shutting down the gas with with a TGMS interlock was required since

3. We perceived inherent difficulty in diluting a full cylinder release, as might be the case with a standard gas panel that could not be shut down by our TGMS.

4. Our researchers would be wielding pitchforks if they were exposed to high levels of F2, even if we explained it was permissible.

I hope this helps.

Best,
Noah

Noah Clay
Director, Quattrone Nanofabrication Facility
University of Pennsylvania

On Mar 3, 2017, at 14:28, Sandrine Martin <sandrine at umich.edu<mailto:sandrine at umich.edu>> wrote:

Hello,

There are a few individual labs here at the University of Michigan that have excimer lasers and use F2 premix gases with 0.1 or 0.2% F2. So far, these gases have been installed in gas cabinets. We are now involved in a new installation and are getting some push back about the need for a gas cabinet.

The argument is made using the Compressed Gas Assoc Pamphlet P-20 Standard for Classification of Toxic Gas Mixtures (2009) that apparently states that, if the LC50 value is over 5,000ppm, the gas mixture is not considered toxic.
Pure F2 is listed with a LC50 (rat, 1h) at 185ppm.
At 0.2% F2, the calculated LC50 is then 92,500ppm, well above the 5,000ppm threshold and the premix is no longer considered a toxic gas. (it also has an NFPA rating of  "1" in health on the MSDS)

Since the mixture is not toxic and the F2 concentration is <1%, EH&S concludes that a gas cabinet is not required.

However, considering that the F2 PEL is 0.1ppm and IDLH 25ppm, it still seems that a gas cabinet would be the safest option and the best solution.

Has anybody gone through similar discussions?
If you have a lab with a fluorine premix gas, is it in a gas cabinet? If not, what type of space is it in, and what kind of ventilation and gas detection are in place?

Thanks
Sandrine


--

Sandrine Martin, Ph.D.

University of Michigan

LNF Managing Director

1246D EECS, 1301 Beal Ave

Ann Arbor, MI 48109

Cell 734-277-2365

Fax 734-647-1781

www.LNF.umich.edu<http://www.lnf.umich.edu/>

@LurieNanofab

_______________________________________________
labnetwork mailing list
labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
https://www-mtl.mit.edu/mailman/listinfo.cgi/labnetwork
_______________________________________________
labnetwork mailing list
labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
https://www-mtl.mit.edu/mailman/listinfo.cgi/labnetwork
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mtl.mit.edu/pipermail/labnetwork/attachments/20170304/bce96b81/attachment.html>