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.
Fire, glass and chemicals? Is there really a question about what should be worn?
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
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