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13649Re: [GPSL] Hydrogen usage

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  • Mark Conner
    Oct 27, 2013
      http://www.mathesongas.com/pdfs/products/Lower-(LEL)-&-Upper-(UEL)-Explosive-Limits-.pdf

      This quotes the 4-75% range as an air mixture.  However, it's also under standardized test conditions and a spark ignition.

      73 de Mark N9XTN


      On Fri, Oct 25, 2013 at 9:18 PM, Zack Clobes <zclobes@...> wrote:


      Is the 4% LEL based on oxygen, or standard ambient air?  If it's looking for 4% oxygen, and there's approximately 20% oxygen in the air, then that would put the ratio back up to roughly 20% air to H2 ratio.

      I don't know myself - I'm basing my assumptions on some tests that I ran a couple of years ago where we induced an "explosion" inside of a small envelope.  I was amazed at how much I had to coerce the hydrogen to do anything with a constant heat source inside the envelope.


      Zack




      On Fri, Oct 25, 2013 at 6:43 PM, James Ewen <ve6srv@...> wrote:
       

      Not wanting to be one to burst your bubble (especially in an explosive manner), but the explosive range of Hydrogen is a little wider than 50/50 (+/- 20-30%).

      The LEL of Hydrogen is 4% and the UEL is 75%.

      LEL is the lower explosive limit, while the UEL is the upper explosive limit.

      The last balloon fill that I did with Hydrogen, I dumped the full bottle to empty in about 2 minutes.

      Keeping any outside atmosphere out of the envelope reduces the risk of explosion by keeping the mixture out of the LEL/UEL range. As long as the hydrogen stays in the envelope, you don't have a problem.

      If however you fill indoors, and the envelope gets ruptured somehow, the hydrogen that was once safely segregated from the oxygen in the atmosphere now can easily become a flammable mixture in the explosive range. Any spark or sufficient heat source can become an ignition point. Indoor filling needs to have a method of rapidly allowing the gas to dissipate. Outdoors, if the envelope bursts, the hydrogen can quickly dissipate and drop below the LEL. There is still a chance of explosion, but it is limited.  

      There are risks, but safe handling can mitigate the risks. Both compressed Hydrogen and compressed Helium stored in high pressure tanks are extremely dangerous if not handled properly, yet most people think of Helium as being "safe". Rupturing a bottle of either product can result in a catastrophe. 

      Play safe!


      On Fri, Oct 25, 2013 at 9:02 AM, Zack Clobes <zclobes@...> wrote:


      My regulator is a single stage, and I don't remember the outlet pressure off hand, but you want as high as you can get, or else you could be there all day filling.  Our balloons fill in about 10 minutes, maybe less.

      As for the static build-up, I have a bit of an issue with that.  For us, we purge our fill line and our balloon of "air" before filling the H2.  So even if there was a spark in the fill line, there is still no oxygen to support combustion.  I've proven that in controlled tests, and it appears that it takes about a 50/50 ratio (+/- 20-30%) of oxidizer and H2.

      To further support this, I (and probably most others) vent our bottles before returning them to the supplier, and I never use a regulator at that point.  I would submit that this is far more dangerous than filling a balloon.

      • Remember that the 2000psi cylinder is your most dangerous component.
      • Fill outdoors.
      • Have an extinguisher handy (not for the H2, but for the latex that could catch fire and fall back to the ground).
      • Be aware.

      Zack Clobes, W0ZC
      Project: Traveler
      www.projecttraveler.org



      On Fri, Oct 25, 2013 at 9:42 AM, Hanson, Douglas R CIV SPAWARSYSCEN-PACIFIC, 63800 <douglas.r.hanson@...> wrote:
      All,
      I would like some help determining the safest use of hydrogen. Hydrogen providers often caution me about static charge buildup if the flow rate into the balloon is too fast. What is considered a safe fill rate? How long should I take in filling a 1600g Hwoyee (assuming I'm only using about 210cu.ft. of gas)? There are many CGA 350 regulators available, but does the outlet pressure of the regulator matter? Single stage or two stage? I look forward to the great feedback. Thank you.

      Ryan, KJ6YXG
      San Diego Near Space Project






      --
      James
      VE6SRV





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