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Previous by Date: Subject: Re: [DCHAS-L] Flashback prevention Date: Tuesday, November 19, 2019 at 6:57:46 PM Author: Richard Palluzi <000006c59248530b-dmarc-request**At_Symbol_Here**LISTS.PRINCETON.EDU> |
Next by Date: Subject: Re: [DCHAS-L] Flashback prevention Date: Tue, 19 Nov 2019 22:45:18 -0500 Author: Eugene Ngai |
I agree with Rich, What are you trying to safeguard against? It's a false sense of safety
In the case of hydrogen it is only when a backflow of air enters the cylinder, otherwise a flame cannot propagate back into the cylinder. How can this happen when you use it at close to atmospheric pressure? In addition even if air entered the cylinder at atmospheric pressure, if an ignition were to occur the resulting overpressure would be 10X the original pressure of the explosive gas mixture. At 15 psig this would result in an over pressure of 150 psig which is well below the 2,000+ working pressure of most cylinders
In the case of acetylene it has an additional hazard that it is unstable and can have a self sustaining decomposition reaction that will cause a cylinder failure, that is why the cylinders are filled with a solid to quench the reaction. If you're using it for an instrument the hazard is much different than a welding torch where oxygen is combined at the torch tip and a backflow due to pressure can occur, The requirements for acetylene cylinder design is that they be able to quench a decomposition reaction from occurring in the cylinder due to a reaction that backflashes into the cylinder. In the testing of acetylene cylinder design the regulations require a backfire test of a fully loaded acetylene cylinder where they actually shoot a flame into the cylinder fully loaded with acetylene. The design fails if it doesn't quench the flame
Eugene Ngai
Chemically Speaking LLC
From: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**PRINCETON.EDU> On Behalf Of Richard Palluzi
Sent: Tuesday, November 19, 2019 6:58 PM
To: DCHAS-L**At_Symbol_Here**PRINCETON.EDU
Subject: Re: [DCHAS-L] Flashback prevention
I can't disagree with your desire to exceed minimum safety requirements but I will question if you are really mitigating any credible risks or just making yourself feel safer. I am not convinced these really provide a much safer environment for most instruments
Sent from my Verizon Wireless 4G LTE Droid
On Nov 19, 2019 11:00 AM, James Saccardo <James.Saccardo**At_Symbol_Here**CSI.CUNY.EDU> wrote:
Steve and Rich,
Irrespective of what the law or code states, we must ask what is reasonable and prudent. It does seem reasonable to put them on the AA, especially since the cost is inexpensive. And if you're going to put them on one flammable gas, you might as well put them on all. The cost is minor and it is a good exercise in safety, and evaluate the piping system. At a time when safety buy-in is meager at best, and in need of a paradigm shift, safety professionals must stand of the side of reasonable and prudent, and then consider "are we in compliance". Nothing wrong with exceeding the requirements of the code. You will never measure the incidents that are prevented, but they will always measure the incidents that occur on your watch.
Consequently, what concentration of hydrogen are you using on your GC?
James
From: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**PRINCETON.EDU> On Behalf Of Richard Palluzi
Sent: Tuesday, November 19, 2019 5:45 AM
To: DCHAS-L**At_Symbol_Here**PRINCETON.EDU
Subject: Re: [DCHAS-L] Flashback prevention
These are only mandatory on welding cylinders. They are designed to protect against a flashback if the hoses fail
Sent from my Verizon Wireless 4G LTE Droid
On Nov 18, 2019 4:59 PM, Steven Smith <e32srs**At_Symbol_Here**MUN.CA> wrote:
Hi All,
One of the instrumentation labs I work in recently had a report suggesting that both the hydrogen and acetylene tanks be equipped with flashback adapters. These are for tanks used for a GC and a Flame AA. The manufacturer, however, suggests that these regulators aren't necessary. I was wondering if anyone on this listserv could comment on whether they use flashback adapters for tanks attached to GC's and FAA instruments.
Thanks,
Steve
Dept of Chemistry
Memorial University
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