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-   -   acetylene and hydrogen gas safety ?? (http://www.allmetalshaping.com/showthread.php?t=10343)

johnptc 12-14-2013 09:24 AM

acetylene and hydrogen gas safety ??
 
I have been warned that it is very dangerous to use hydrogen gas in any equipment that was previously used with acetylene.

Does any one know the details of why this might lead to an explosion :confused:

crystallographic 12-14-2013 07:55 PM

Quote:

Originally Posted by johnptc (Post 86156)
I have been warned that it is very dangerous to use hydrogen gas in any equipment that was previously used with acetylene.

Does any one know the details of why this might lead to an explosion :confused:

Welcome JM,
I've heard the warning for years, not to put H2 through a hose or torch that has seen use with Acet because it can go BLAM. I cannot give you the chemistry on that, but the airlines are very careful about transporting O/A welding torches and hoses because of the acetylene residues. Perhaps acetone from the acet will mingle with hydrogen in the form of peroxide?

I also cannot give the chemistry of how chlorinated hydrocarbons turn into phosgene gas in the presence of high frequency (TIG) welding, but I don't use brake cleaner around the TIG.

johnptc 12-14-2013 09:43 PM

wiki on phosgene ( UV and chlorinated compounds)
 
Upon ultraviolet (UV) radiation in the presence of oxygen, chloroform slowly converts into phosgene by a radical reaction. To suppress this photodegradation, chloroform is often stored in brown-tinted glass containers. Chlorinated compounds used to remove oil from metals, such as automotive brake cleaners, are converted to phosgene by the UV rays of arc welding processes.[8]
Phosgene may also be produced during testing for leaks of older-style refrigerant gases. Chloromethanes (R12, R22 and others) were formerly leak-tested in situ by employing a small gas torch (propane, butane or propylene gas) with a sniffer tube and a copper reaction plate in the flame nozzle of the torch. If any refrigerant gas was leaking from a pipe or joint, the gas would be sucked into the flame via the sniffer tube and would cause a colour change of the gas flame to a bright greenish blue. In the process, phosgene gas would be created due to the thermal reaction. No valid statistics are available, but anecdotal reports suggest that numerous refrigeration technicians suffered the effects of phosgene poisoning due to their ignorance of the toxicity of phosgene, produced during such leak testing.[citation needed] Electronic sensing of refrigerant gases phased out the use of flame testing for leaks in the 1980s. Similarly, phosgene poisoning is a consideration for people fighting fires that are occurring in the vicinity of freon refrigeration equipment, smoking in the vicinity of a freon leak, or fighting fires using halon or halotron.

crystallographic 12-15-2013 12:31 AM

chemistry
 
Quote:

Originally Posted by johnptc (Post 86204)
Upon ultraviolet (UV) radiation in the presence of oxygen, chloroform slowly converts into phosgene by a radical reaction. To suppress this photodegradation, chloroform is often stored in brown-tinted glass containers. Chlorinated compounds used to remove oil from metals, such as automotive brake cleaners, are converted to phosgene by the UV rays of arc welding processes.[8]
Phosgene may also be produced during testing for leaks of older-style refrigerant gases. Chloromethanes (R12, R22 and others) were formerly leak-tested in situ by employing a small gas torch (propane, butane or propylene gas) with a sniffer tube and a copper reaction plate in the flame nozzle of the torch. If any refrigerant gas was leaking from a pipe or joint, the gas would be sucked into the flame via the sniffer tube and would cause a colour change of the gas flame to a bright greenish blue. In the process, phosgene gas would be created due to the thermal reaction. No valid statistics are available, but anecdotal reports suggest that numerous refrigeration technicians suffered the effects of phosgene poisoning due to their ignorance of the toxicity of phosgene, produced during such leak testing.[citation needed] Electronic sensing of refrigerant gases phased out the use of flame testing for leaks in the 1980s. Similarly, phosgene poisoning is a consideration for people fighting fires that are occurring in the vicinity of freon refrigeration equipment, smoking in the vicinity of a freon leak, or fighting fires using halon or halotron.

Ah, finally a cogent explanation. Thank you, JM. Excellent as usual. Good to have you back.

Um Halon is a common auto xt'guish'r, with use-associated proximity to electricicles.... cough.

Acetone peroxide is a primary, with brisk exothermics.


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