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

[Dan P. Woodie]

Sandrine,

We have multiple installations across the College of Engineering, ranging from 10% to 0.1% F2 concentration, and have gone with and without gas cabinets based on the situation. I concur with most of the assessments presented so far. That PEL limits and exposure risks are paramount in a decision, and they trump other regulatory allowances. But even with that, I had to admit that at some point, the concentration gets low enough that you can be safe without a gas cabinet.

In this case, it was for a 0.2% concentration. The cylinder was going to be kept closed most of the time, with limited staff performing the laser cavity refills every 3 – 4 months. We ended up going with the smallest Flow Restrictive Orifice (FRO) for the gas cylinder and doing calculations on the peak room concentration based on the air exchange rate in the space. Attached is a graph with my calculations for this. Based on this, the peak concentration ended up being under 5 ppm, which is still above the PEL, but not too far above the STEL (15 minutes) of 2 ppm. The FRO also helped keep the peak level from hitting too quickly, in this case, it would take about 5 minutes to reach that level.

Even with those safeguards, we choose to install a single gas detector with a simple visual and audible alarm to inform people to leave the lab if there was a release. We felt that the combination of the RFO, the room ventilation levels, and the alarm were enough to provide proper warning. Other situations where a gas cabinet was easier to install or the concentration was higher we went the full route. In this case, based on cost, this was a reasonable level of precaution that the researchers could afford (<$3k) while an installed gas cabinet would have run 10X or more of that.

Happy to discuss further if you want to give me a call or a follow-up email.

Dan

Daniel Woodie
Safety Manager, College of Engineering

From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Sandrine Martin
Sent: Friday, March 03, 2017 2:29 PM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] Gas cabinet for F2 premix for excimer lasers?

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
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