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

[Noah Clay]

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
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