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Flow rate calculation of hydrogen gas in case of leak

  1. May 29, 2018 #1
    Hi. I'm a mechanical engineer, but working as Safety Engineer. I have a question how to calculate the flow rate of hydrogen gas before a flow controller in case of leak through a 4.5 mm line at 35 bar pressure. Thanks in advance.
     
  2. jcsd
  3. May 29, 2018 #2

    ChemAir

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    What will the result of this calculation be used for?
     
  4. May 29, 2018 #3

    berkeman

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    Thread closed temporarily for Moderation...
     
  5. May 29, 2018 #4

    berkeman

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    Welcome to the PF.

    Your post is a bit worrisome. Your Profile page shows that you have a BSME, but you are needing to ask on a web forum how to do a basic gas flow rate calculation? Did they not cover that in your undergrad ME classes?

    And in your country, are there not Professional Engineer exams and qualifications/certificates for the position of Safety Engineer? Since your work sounds like it could affect the life safety of your coworkers, it would seem that such a PE certification would be a routine requirement...

    And what he said...
     
  6. May 29, 2018 #5
    To verify if the walkin fumehood is capable to exhaust the hydrogen gas in case of leak. Thank you.
     
  7. May 30, 2018 #6

    256bits

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    In addition to @berkeman comments, and @ChemAir, it would seem that your question is perhaps not quite complete.
    It is a bit too terse what you are trying to accomplish.
    Have a sit down, and write down on paper what would be, or could be, the problems associated with a gas leak.
    Are there standard regulations to follow?
    Why have you been assigned this task. From whom? Plant supervisor? Lab supervisor? ??
    what do they want, and have asked you to do?
    Maybe you already know, and are assuming others know also.
    You might be more interested in the fumehood capability calculations, and resulting air mixtures surrounding the leak.
    Are you interested in asphyxiation, explosive gas mixtures, maybe something else?
    With a full blown hose rupture, what are procedures to evacuate the area, or maybe even the building? would that even be necessary?
    Who contacts emergency responders? Is that necessary?
    How much hydrogen on site?
    Like, how far down the line are you supposed to go with this.

    I know nothing about nothing about nothing here, but even so, these contemplative points do come to mind.
    How far have you progressed so far.
     
  8. May 30, 2018 #7

    ChemAir

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    Project tasks that include "life safety" and involve safety systems, controls, interlocks, alarms, etc., can be a pretty complicated field to navigate, and small problems (Can my hood remove all the hydrogen that could leak out?) can't be considered in a vacuum.

    Some things worth considering, some redundancy to @256bits thoughts :
    -What was the original design basis for the hood? Is the design adequate for use before adding a hydrogen leak to its capabilities? Is the hood design suitable for the presence of significant amounts of hydrogen (no ignition sources)? Is the hood configuration such that it is unlikely to trap hydrogen in places?
    -Does this hood have other uses at the same time?
    -Is it normally occupied by person(s), and what level of PPE do they wear?
    -Are there hydrogen leak detectors in the hood? Should there be? What type? Calibrated how frequently?
    -If the power to the lab shuts off, what happens to the hydrogen/hood system?
    -What is the source of the hydrogen? Is it large enough to fill the room (or the building) if the hood stops working? Could the leak cause the hydrogen source some type of problem?
    -Should there be an interlock/shutdown when a leak is detected? What all, specifically should be shut down? What order should they be shut down? When I do this, does this cause any other new problems that weren't there before? Are there other chemicals, reactions, testing in the same vicinity that could have incompatible materials present?
    -Will there be preventive maintenance to verify the hood performs as it should?
    -Will this require re-training of affected personnel?

    While some concerns seem a little excessive, others probably are not, and you should be considering the larger picture, weighing things appropriately.

    Here in the US, I would encourage someone who is out of their element on these issues to look into the following:
    1) Contact the supplier of the hydrogen. Manufacturers under the Responsible Care standard will provide some degree of guidance, training, etc. on the safe use of their chemicals. This guidance could include auditing an installation or an installation plan. A hydrogen supplier will be current on SDS and engineering controls technology. This is likely to be your best resource if they are a large supplier. If your current supplier can't provide this, it may be worth considering an alternate, if possible.
    2) Contact someone at your company or institution who is responsible for questions about insured risk. There is usually an insurance representative/agent/inspector that could provide guidance. They will have a stake in bringing in a new risk, as it could affect insurance requirements.

    If these are unsuccessful, it may be time to call an engineering company that can bring some expertise.
     
  9. May 30, 2018 #8

    berkeman

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    Yeah, intrinsically safe walk-in fume hoods do look to be available, but you probably need to be sure it is designed for that (switches, lights, blower, etc.). One example:

    http://www.fume-hoods.net/walk-in-f...MIwquoy9qt2wIVl9lkCh2Yvg4BEAAYAyAAEgLIEvD_BwE

    walkin-fume-hood.jpg
     
  10. May 30, 2018 #9
    Thanks for the comment. Would love to hear from you what formula to use wherein only line pressure and diameter is given.
     
  11. May 30, 2018 #10

    berkeman

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    Do you understand the explosion risks and safety issues mentioned above by others?
     
  12. May 30, 2018 #11
    Sorry for not putting all the information which I admit is my mistake of not reading thoroughly the forum rules.
    My inquiry is the result of Hazard Operability Study (HAZOP) conducted on bench scale reactor inside the walk-in fume hood.
    HAZOP team raised a recommendation to verify if the fume hood is capable to vent the hydrogen in case of accidental leakage else, hydrogen detector will be installed outside the hood that will be connected to the Central Fire and Gas Detection System.
    By the way, the walk-in fume hood is designed as per NFPA standard. Inspection frequency is done as per OSHA with current face velocity at 200 fpm.
    It so happen that I came accross this informative site.
    Can you now please advice what formula to use?
     
  13. May 30, 2018 #12
    In the profile question, there are no alternative answer in the dropdown list for "Education in Progress" and "Completed Educational Background".
     
  14. May 30, 2018 #13

    anorlunda

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    I believe that you can use this calculator for that problem. https://www.pipeflowcalculations.com/gasleak/
     
  15. May 30, 2018 #14

    berkeman

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    There are many NFPA standards. Is your hood approved as intrinsically safe and explosion proof?
     
  16. May 31, 2018 #15

    256bits

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    The good thing about hydrogen is that being so light it will disperse more readily than other vapourized fuels.
    That also makes it a bad thing as it can follow into nooks and cranies where other fuels will not, such as open pipes.
    The bad thing about hydrogen is that an explosive mixture with air ranges from about 4% to 74 %., or rather flammability in air.

    Being colorless and odourless hydrogen in the air is not detected by human senses.
    A small electrical discharge can ignite the air-fuel mixture

    See chart here, for comparison with a few other fuels:
    https://www.energy.gov/eere/fuelcells/safety-codes-and-standards-basics
    for dispersion coefficient in air, etc.

    I do wonder how a leak rate can be correlated with the hazard within and around the hood.
    Thing is to make sure there never( never say never ) is a leak, all connectors are standard for hydrogen, methods are followed.
    Tanks are stored properly and connections are not forced.
    If a leak, shutdown immediately.

    I would say that safety protocol is a bunch lot more than leak rate, but should include everything from start to finish and followup for a safe work environment.
    HAZOP should have knowledge, and educate all on the team.
    Do they have a recommendation on reactor startup such as maximum leak rate before reactor startup = 0.
     
  17. May 31, 2018 #16
    Hood Specification: NFPA 45 / ASHRAE 110 / ASTM E84 to comply with NEC / NFPA 70, Class I locations where flammable gasses or vapors may be present in the air in quantities sufficient to produce explosive or ignitable mixtures.
     
  18. May 31, 2018 #17
    Leak scenar
    I understand your concern. HAZOP study was done by a team of subject matter expert from research, technology, EHS including the designer of bench scale reactor.
     
  19. May 31, 2018 #18
    Problem solve through the use of gas dispersion modeling software. Sorry for creating this thread that goes nowhere.
    Lesson learned: Lot of talks will not solve the problem.
    Got more work to do.
    Thanks
     
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