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Previous by Date: Subject: Re: [DCHAS-L] Flashback prevention Date: Tuesday, November 19, 2019 at 10:29:50 PM Author: Eugene Ngai <eugene_ngai**At_Symbol_Here**COMCAST.NET> |
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A flash arrestor works by conducting enough heat away from the flame to quench the reaction. Gases with high flame speed have large flash arrestors, these are acetylene and hydrogen. The length of the arrestor has to account for the time it takes to transverse the distance to allow thermal conductance to conduct the heat
Eugene Ngai
Chemically Speaking LLC
www.chemicallyspeakingllc.com
-----Original Message----- My experience is that flame arrestors are frequently used with on-line analyzers that are connected to a process for continuous on-line monitoring. This need does depend on the analyzer technology and the analyzer manufacturers approvals. When required, the arrestors are fitted at the sample inlet to the analyzer. With a GC, there is not commonly a direct connection to the process from the analyzer, being isolated by the injection valve. In the event, the injection flows are very small (5-100ë1Ú4l per measurement cycle) and dead volume on the sample inlet side is extremely critical. The use of hydrogen with GC‰??s is usually as carrier gas but can also be as fuel gas, in either case we are talking about very high purity hydrogen. I have never seen flame arrestors in these lines between the H2 cylinders and the analyzer. Where analyzers vent to a hazardous area, it is not uncommon to have a flame arrestor in the vent header, however these do give ongoing maintenance and are frequently removed (post installation) There is a catch 22 with these devices, those that are tested and approved to a standard, invariably are tested with an explosive mixture of the flammable in air. As example, the flame transmission test for group C, D gases is usually done with a group B gas. In principle, It, should be possible to carry out tests for a group B gases with a group B gas supercharged with Acetylene but I have not come across such as commercially available. The other insurmountable problem is, that those standards that are available are for large devices to be fitted on much larger line sizes than those to be encountered in normal analyzer sample lines. As such these commercially available arrestors tend to be large, much too large for small analyzer flows. In consequence, when required, the analyzer manufacturer supplies dedicated devices for the purpose - I am not aware that these meet or are designed to a any kind of recognized international standard. Int +44 759 412 4934 From: ACS Division of Chemical Health and Safety Steve and Rich, Consequently, what concentration of hydrogen are you using on your GC? From: ACS Division of Chemical Health and Safety 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 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 Confidentiality Warning: --- ---
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From: ACS Division of Chemical Health and Safety
Sent: Tuesday, November 19, 2019 12:50 PM
To: DCHAS-L**At_Symbol_Here**PRINCETON.EDU
Subject: Re: [DCHAS-L] Flashback prevention
James Osprey, C. Phys, C. Eng.
Technical Advisor
ospreyj**At_Symbol_Here**novatech.ca
Sent: November-19-19 5:00 PM
To: DCHAS-L**At_Symbol_Here**PRINCETON.EDU
Subject: Re: [DCHAS-L] Flashback prevention
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.
James
Sent: Tuesday, November 19, 2019 5:45 AM
To: mailto:DCHAS-L**At_Symbol_Here**PRINCETON.EDU
Subject: Re: [DCHAS-L] Flashback prevention
Hi All,
Memorial University
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