All MetalShaping

Go Back   All MetalShaping > General Metal Shaping Discussion > Shop Safety
  Today's Posts Posts for Last 7 Days Posts for Last 14 Days  

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 12-14-2013, 10:24 AM
johnptc johnptc is offline
Member
 
Join Date: Dec 2013
Location: Los Angeles, CA
Posts: 61
Question 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
__________________
John Marcus

Last edited by johnptc; 12-14-2013 at 02:06 PM.
Reply With Quote
  #2  
Old 12-14-2013, 08:55 PM
crystallographic crystallographic is offline
MetalShaper of the Month October '14 , April '16, July 2020, Jan 2023
 
Join Date: Dec 2010
Location: Western Sierra Nevadas, Badger Hill, CA
Posts: 4,388
Default

Quote:
Originally Posted by johnptc View Post
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
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.
__________________
Kent

http://www.tinmantech.com

"All it takes is a little practical experience to blow the he!! out of a perfectly good theory." --- Lloyd Rosenquist, charter member AWS, 1919.
Reply With Quote
  #3  
Old 12-14-2013, 10:43 PM
johnptc johnptc is offline
Member
 
Join Date: Dec 2013
Location: Los Angeles, CA
Posts: 61
Exclamation 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.
__________________
John Marcus
Reply With Quote
  #4  
Old 12-15-2013, 01:31 AM
crystallographic crystallographic is offline
MetalShaper of the Month October '14 , April '16, July 2020, Jan 2023
 
Join Date: Dec 2010
Location: Western Sierra Nevadas, Badger Hill, CA
Posts: 4,388
Default chemistry

Quote:
Originally Posted by johnptc View Post
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.
__________________
Kent

http://www.tinmantech.com

"All it takes is a little practical experience to blow the he!! out of a perfectly good theory." --- Lloyd Rosenquist, charter member AWS, 1919.

Last edited by crystallographic; 12-15-2013 at 01:39 AM.
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT -5. The time now is 06:22 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.