[labnetwork] H2 Generators

[Abbie Gregg]

Yes, the flow restricting orifice is key, as well as an excess flow sensor in the hydrogen lines, regardless of the source.

Abbie Gregg
President
Abbie Gregg, Inc.
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email agregg at abbiegregg.com<mailto:agregg at abbiegregg.com>
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From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Rizik
Sent: Wednesday, July 18, 2012 6:11 PM
To: 'Grimard, Dennis'; labnetwork at mtl.mit.edu
Subject: Re: [labnetwork] H2 Generators

The average cost runs about $6,500 per gas sensor including hardware, programming, sensor, wiring, conduit, functional testing, commissioning, etc. Pull Stations and horn/strobes each runs about $1,500 installed.

You really got a point there. And yes, you will need to place gas sensors to overlap in the area of work so that they will not miss a gas leak. Although this is quite difficult to achieve, you try to install welded tubing from the generator to the point of use then provide as sensor at each point. Again, cost will be an issue. In a previous email, I mentioned that the gas monitoring system shall be interlocked with the generator to ensure that it shuts down upon gas detection, manual activation and fire alarm signal initiation.

One more item to consider, is installing an orifice in the tubing leaving the generator to ensure that we do not allow more than 150% of the process gas demand to be supplied to the tools. On past projects, we installed excess flow mechanical valves that would trip if H2 flow rate exceeds a preset limit. This will allow us to limit H2 leakage to a level that would not exceed 25% of the LEL concentration in the lab space. All these parameters MUST be taken in consideration by the engineer of record. Occasionally, these parameters are overlooked and are only discovered during the plan review cycle by the AHJ.

Regards

Rizik Michael, PE
Principal
Integrated Engineering Services
Office: +408 261 3500, Ext. 201
Cell:      +408 718 0927


From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Grimard, Dennis
Sent: Wednesday, July 18, 2012 1:37 PM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] H2 Generators

All:

I have been watching the discussion regarding H2 generators.  Although I agree with most of what has been said I worry about being able to shut off the generator in case of a leak.  The generator does not know that it is delivering into a leak and unless the leak is detected then the generator will continue pumping to that leak.  Adding detectors is not the solution.  H2 detectors are difficult to place such that they will pick up a leak.  Do you add detectors at every possible leak point?  Add in the high velocities of the cleanroom and I hesitate to change from bottles to generators.

When considering the costs, you also have to consider the cost of the added detectors ... which are not cheap ...

Dennis Grimard, Ph.D.
Managing Director
Lurie Nanofabrication Facility
1246D EECS Blding
1301 Beal Avenue
Ann Arbor, MI 48109-2122
(734) 368-7172 Cell
http://www.lnf.umich.edu

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