[labnetwork] Question about toxic gas sensors inside fab

[Dan P. Woodie]

Sandra,

Here are some best practices for gas detection that I can share based on my 25+ years working with various systems and manufacturers. Your local, state, and Federal Building and Fire Codes will ultimately dictate many requirements for gas detection of hazardous gases and most best practices cover code requirements and beyond, but you still need to check in with your local experts and Authority Having Jurisdiction (AHJ).

Generally, you want to have all areas where the hazardous gases are used or stored covered by both ambient and exhausted enclosure gas detectors. Ambient points cover the air your users and employees are breathing, and the exhausted points are monitoring the air inside the exhausted enclosures (gas cabinets, tool enclosures, etc.) where the gas is piped / stored to notify you of leaks at those connections. Detectors for adjacent spaces / tools can be combined in some cases, to reduce the number required, such as adjacent tools that share an exhaust duct having a common gas monitor on it. Similarly, you need to examine the spacing of your ambient detectors, as they can cover a larger area based on airflows. When I was at Cornell and we had to replace all our gas detectors (late 2000's), we rented a DI water fogger to examine where the "prevailing winds" blew through our service aisles and determined that a single ambient detector could cover several tools on both the cleanroom and service chase sides if the location carefully selected.

Codes (and best practices) generally only requires ambient detection near potential leak points such as mechanical connections and points of use (all of which should only be in exhausted enclosures), not along the length of welded and leak checked piping. Best practices for toxic gases are orbitally welded stainless steel pipe that is helium leak checked<https://en.wikipedia.org/wiki/Helium_mass_spectrometer>, with double-walled piping to help provide an additional layer of protection. The integrity of the double-walled pipe is often monitoring by pulling the annular space to either vacuum or pressurizing with an inert gas and monitoring the pressure level of that space at the source. A loss of vacuum or pressure would alarm, indicating either mechanical damage to the exterior pipe, or corrosion of the interior pipe.

Generally, codes require you monitor for all gases rated as toxic, highly toxic, pyrophoric, or flammable as defined by your codes. It is generally a good idea to also treat gases that fall through these definitions as hazardous (gas cabinets and detectors) such as ammonia and carbon monoxide. These gases make you ill at levels similar to toxic gases but take long enough to kill you that they slip through the toxic designation.

I hope this helps answer your broad inquiry on this topic. I am happy to discuss further if you want to reach out directly.

Dan

Daniel Woodie
Director, Micro/Nano Fabrication Center, Princeton Materials Institute
Princeton University
155 Andlinger Center
86 Olden St
Princeton, NJ 08540

(609)258-5922 (office)
(607)227-2993 (cell)
daniel.woodie at princeton.edu<mailto:daniel.woodie at princeton.edu>
mnfc.princeton.edu<https://mnfc.princeton.edu/>
www.linkedin.com/in/danielpwoodie<http://www.linkedin.com/in/danielpwoodie/>



From: labnetwork <labnetwork-bounces at mtl.mit.edu> On Behalf Of Malhotra, Sandra Guy
Sent: Tuesday, January 28, 2025 4:11 PM
To: Fab Network <labnetwork at mtl.mit.edu>
Subject: [labnetwork] Question about toxic gas sensors inside fab

Howdy All,
We would like to understand the types of toxic gas sensors that are used inside academic fabs near tools or gas lines. These would be in addition to those inside toxic gas cylinder cabinets.

We would appreciate learning which tools/toxic gases are monitored inside your fabs and where the monitors are located. Any assistance would be greatly appreciated!

Thanks for your time,


Sandra G. Malhotra, Ph.D.  |  Senior Laboratory Manager



We would greatly appreciate an acknowledgement of your work in AggieFab:  "The nanofabrication was conducted in the Texas A&M University AggieFab Nanofabrication Facility (RRID:SCR_023639), which is supported by the Texas A&M Engineering Experiment Station and Texas A&M University."



AggieFab Nanofabrication Facility

https://aggiefab.tamu.edu/

Department of Electrical & Computer Engineering, College of Engineering | Texas A&M University

3253 TAMU | College Station, TX 77843

ph: 979.845.3199  |  sandra.malhotra at tamu.edu<mailto:sandra.malhotra at tamu.edu>



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TEXAS A&M UNIVERSITY | FEARLESS on Every Front



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