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Previous by Date: Subject: Re: [DCHAS-L] PNNL Hydrogen Fire Event Video Date: Tuesday, January 29, 2019 at 11:36:11 AM Author: Ken Kretchman <kwkretch**At_Symbol_Here**ncsu.edu> |
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I agree that this is a great video--one I'll be sharing for the lessons we can apply--but there is one error that bothers me, in part because it highlights a (common?) misunderstanding. At about 2:30, a statement is made that there is 50 psi in the house line and that "the pressure was greatly reduced to 200 sccm" at the mass flow controllers.
That metric is a flow rate, NOT a pressure. One could have that flow rate at any pressure one wanted. I am saddened to see that this error made it through all of the editing and all the SMEs who presumably saw it before release.
Could that (misunderstanding what the equipment actually controls) have been a factor in allowing/continuing conditions that lead to the equipment failure? Possibly, but I don't have enough context.
Could that misunderstanding lead to someone else's incident? It certainly could.
I argue that that operators, SMEs, and investigators should know the importance of such distinctions. Saying system component X controls process variable Y when it actually controls process variable Z is a quick way to run into problems if you want to actually control Y. Y might be controlled indirectly, but the relationship between Y (e.g. pressure) and Z (e.g. mass flow) may depend on a number of known and unknown factors (upstream pressure, downstream pressure, flow restrictions, etc.), but if something (un)expectedly changes (e.g. tubing leaks and now there are no or fewer restrictions downstream) all bets are off on whether one can actually control what one wants. Far better to realize what is actually being controlled, and then proceed with the analysis of what could go wrong armed with information that reflects physical reality.
Is that actually the issue here? Maybe not, but the only way a community can help ensure that others recognize such errors is to point them out.
If nothing else, my favorite quote applies here: "Precision in language reflects clarity of thought." -Prof. Scott Denmark
Timothy J. Kucharski, Ph.D.
High-Hazard Lab, Senior Technical Lead
Chemical Hygiene Officer
Aramco Services Company
Advanced Materials Team
Aramco Research Center - Boston
Tel.: 713 432 5472 || 857 270 8308
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From: ACS Division of Chemical Health and Safety [mailto:DCHAS-L**At_Symbol_Here**PRINCETON.EDU] On Behalf Of Stuart, Ralph
Sent: Tuesday, January 29, 2019 9:26 AM
To: DCHAS-L**At_Symbol_Here**PRINCETON.EDU
Subject: Re: [DCHAS-L] PNNL Hydrogen Fire Event Video
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> One of the points they mentioned a bit casually is that plastic tubing has no fire resistance and little mechanical strength.
Another point that I thought was understated as part of the incident report was the problem presented by storage of chemicals (gas cylinders in this case) not involved in the process within the fume hood. While fume hoods are designed to serve many different uses, they aren't designed to host more than 1 at a time. Storing gas cylinders in a fume hood is not a good use of valuable hood space. I've observed that it's a common practice that I don't quite understand. The colliery fume hood lesson learned in this story is that fume hoods aren't designed to provide any protection from fire other than segregation of the process from other chemicals.
I really appreciate the effort that went into making this video and sharing it with the community. I'm always fascinated by how many different kinds of lessons learned can be developed from the same incident, depending on the level of detail and transferability of the Lesson desired.
- Ralph
Ralph Stuart, CIH, CCHO
Environmental Safety Manager
Keene State College
603 358-2859
ralph.stuart**At_Symbol_Here**keene.edu
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