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Subject: Re: [DCHAS-L] "Hydrogen pop" demo and PPE
Date: Sunday, January 3, 2021 at 12:19:55 PM
Author: Daniel Crowl <crowl**At_Symbol_Here**MTU.EDU> 		Next by Date:
Subject: Re: [DCHAS-L] "Hydrogen pop" demo and PPE
Date: Sun, 3 Jan 2021 12:46:10 -0700
Author: Daniel Crowl

From: Jarral Ryter <jryter**At_Symbol_Here**WESTERN.EDU>
Subject: Re: [DCHAS-L] "Hydrogen pop" demo and PPE
Date: Sun, 3 Jan 2021 18:05:01 +0000
Reply-To: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU>
Message-ID: 6c556bb812204a42aa02f79511617782**At_Symbol_Here**mail.wsc.western.edu
In-Reply-To


Ok. Get on with it..... this has been done for decades (century?) in school science classes. Any one ever hear of an accident? Like we see with burning methanol with metal salts? Is saying a hundred more times what the ppe needed going anywhere at this point? Or that you shouldn't do it? People are going to do it. 

I did it way way back. It was an obvious test for hydrogen. CO2 gasses made, put out flames when putting a burning splint in. Kids are doing it now in freshman science at our public school. I asked. 

Sorry to vent.... 

As far as the original question. A picture of the flame with very fast timing or time exposure could look cool. The flame probably would be hard to see though... of course do it behind an explosion shield. I guess that was the original thought to take a better picture?

Jarral Ryter 





Sent from my Verizon, Samsung Galaxy smartphone



-------- Original message --------
From: Daniel Crowl <crowl**At_Symbol_Here**MTU.EDU>
Date: 1/3/21 10:38 AM (GMT-07:00)
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Subject: Re: [DCHAS-L] "Hydrogen pop" demo and PPE

NOTICE: This email originated from outside of the University. Do not click links or open attachments unless you recognize the sender and know the content is safe. Thank you, Western IT Services.
Hi All,

I would like to comment on the hydrogen POP demo and warn everyone about the possibility of a hydrogen detonation.

I was on the ASTM E27 committee for many years - this committee handles all the ASTM flammability standards -  and there was always a continuing discussion about hydrogen making a transition from a deflagration to a detonation.

The demo video that I watched was of a hydrogen deflagration - with the combustion occurring at a speed less than the speed of sound.  It is possible for hydrogen to make a transition to a detonation - with the combustion burning at or greater than the speed of sound - upon which the glass tube would immediately explosively shatter, even with the open end. 

Hydrogen is prone to this phenomenon since it burns much faster than other gases.  This is demonstrated by a bigger "pop" with hydrogen than, lets say, methane.

Most of the evidence of a hydrogen detonation is from anecdotal case histories.  No one knows how to even construct an experiment to study this.

What is known about this phenomenon is:

1.  It is more likely to occur in tubes or pipes with one closed end.  The closed end causes pressure piling and the transition to a detonation.  The glass tube in the demonstration is closed at one end.  A louder "pop" is obtained in the demo with the closed end due to this pressure piling. 
2.  It is more likely to occur with enriched oxygen since this increases the burning speed of the hydrogen.
3.  The longer the tube or pipe the more likely the transition will occur.
4.  It is not clear how the tube diameter affects this.

I would say that the probability of a transition to detonation is unlikely for this demo, as shown in the video.  

However, I can see someone increasing the tube length and using oxygen to increase the "pop."

Why is this demo even being done?  What does it demonstrate?  I realize it has a high "fun factor." 

Dan Crowl
Emeritus Professor,  Michigan Tech University.

On Sat, Jan 2, 2021 at 7:04 PM Landgrebe, Virginia HS Teacher - Science <landgrebev**At_Symbol_Here**newmilfordps.org> wrote:
Fire, glass and chemicals? Is there really a question about what should be worn?


On Tue, Dec 29, 2020 at 12:19 PM Kemsley, Jyllian <J_Kemsley**At_Symbol_Here**acs.org> wrote:

Hi all--I'd appreciate any thoughts on someone wearing just eye protection for this demo. On the one hand, it's a small amount and the test tubes don't have constricted necks. On the other hand, it looks like a glass tube held in bare hands near the face.

 

https://twitter.com/I_am_Endeavour/status/1340788101283803140

 

It's been suggested as something to post in C&EN's "Chemistry in Pictures" collection for New Year's Eve, and I need to decide by tomorrow (Wednesday 12/30) whether to go ahead.

 

Thanks for your input!

Jyllian

 

Jyllian Kemsley, PhD [she/her/hers]

Executive Editor, policy and content partnerships

Chemical & Engineering News

M:  (+1) 925-519-6681 | Skype: jyllian.kemsley

Twitter: **At_Symbol_Here**jkemsley

Want to be in the know? Sign up for C&EN’s weekly newsletter: cenm.ag/censubscribe

 

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