My welding supply store warns AGAINST using a soapy water solution
to check for leaks on bottled gases, especially oxygen…UNLESS one
is absolutely certain that it is a NON PETROLEUM based soap being
used such as liquid Ivory.
I can’t relay their explanation in detail but the jist of it has to
do with the gases moving into the regulators with such
speed/pressure (especially the oxygen.) that the "friction"
generates enough heat to ignite petroleum residue. They note of
course that this is undesirable since open flame and bottled gases
don’t mix well.
This said I will be the first to admit that I have for years used
"any old liquid soap" and water mixture to test propane connections
and have had no problems. But believing that old dogs can learn new
tricks…sometimes, I have heeded the warning and now use only
non-petroleum based liquid soap. Can’t be too safe with these gas
(The welding shops also sell bottles of safe solutions for leak
Joe Battle Ground, WA where it’s unseasonably sunny and warm.