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

Wed Mar 8 10:15:22 EST 2017

I agree with Dennis' logic. A gas cabinet or exhausted enclosure is the
preferred installation. However, installing the gas cylinder in, say
10'x10'x10' room  could work if we treat the room as an exhausted enclosure
with proper safeguards. This includes proper exhaust and make up air
distribution to minimize dead zones within the room. 

Perhaps the cylinder could be installed in 4'Wx3'Lx8'H closet which is
closer to a gas cabinet size. Keep in mind that such a closet will have to
be designed and built with similar features as a gas cabinet. This includes
automatic door closure; air intake louvers at the bottom of the door; proper
exhaust flow rate to ensure less than 1/2PEL in the event of a leak since
for personnel protection; gas monitoring sensor; and interlocking the access
door with the gas monitoring system. The cost of building such a closet will
far exceed the cost of a gas cabinet or exhausted enclosure.

Regards

Rizik Michael, PE

Principal

Integrated Engineering Services

Office: 1-408 261 3500, Ext. 201

Cell:     1-408 718 0927

From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu]
On Behalf Of Dennis Grimard
Sent: Saturday, March 4, 2017 8:12 AM
To: Noah Clay
Cc: labnetwork at mtl.mit.edu
Subject: Re: [labnetwork] Gas cabinet for F2 premix for excimer lasers?

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

On Mar 4, 2017, at 9:04 AM, Noah Clay <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> 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

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

@LurieNanofab

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