[labnetwork] Combined or separate exhaust?

[Dan P. Woodie]

Travis,

In general, your local codes will drive most of these answers more than general opinion, but I have seen both. At my previous institution (Cornell), the 2003 era building had gas cabinets and process tools on the same exhaust, but divided into several different types: corrosive exhaust in fiber reenforced plastic duct (i.e. fiberglass, FRP), solvent exhaust in SS, silane exhaust in a dedicated SS duct, and vacuum pump exhaust for the general process tools (post scrubbers). Each of those systems had a 100% redundant fan, with automatic switchover for wear leveling and the ability to do maintenance on one without impacting operations.

At my current location (Princeton), everything is in one system with SS duct, but with the same 100% redundant fan with switchover for maintenance and wear leveling. We do have a separate pair of fans for our gas bunker, where most (but not all) of our gas cabinets are located. Newer codes and some jurisdictions may require catastrophic exhaust abatement on the gas cabinet exhaust, so that is something to consider with your ducting plans. Given the amount of maintenance that fans require per year, having the redundancy to avoid tools and processing shutdowns constantly is worth the investment. Additionally, carrying the load with a single fan often helps to hit the jet velocity that designers are generally seeking, to ensure the exhaust clears the standard thermal plume / recirculation that most buildings have. Multiple fans running at lower volumes may have a harder time getting to the recommend ft/sec.

Dan

Daniel Woodie
Director, Micro/Nano Fabrication Center, Princeton Materials Institute

From: labnetwork <labnetwork-bounces at mtl.mit.edu> On Behalf Of Massey, Travis
Sent: Monday, February 24, 2025 9:24 PM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] Combined or separate exhaust?

Hi all,

LLNL is planning a significant cleanroom expansion, and the question arose whether we need separate exhaust for hoods and tools/gases, or if they can be combined into a single shared exhaust.  Or do you have a single exhaust with 2+ exhaust fans pulling simultaneously, so there's always some exhaust air moving if one fan is down?  The conventional wisdom around here has its share of holes, so I'm out to learn from the broader nanofab cleanroom community.  How are your cleanrooms' exhaust systems are configured, especially if you've had to go down this cleanroom design rabbit hole?

I'm also broadly open any other lessons learned regarding provisioning exhaust or other utilities - whatever you feel like sharing.  Too much information during the design phase is far better than too little.

Thanks,
Travis Massey
Center for Micro and Nano Technology (CMNT)
Lawrence Livermore National Laboratory (LLNL)
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