As this was brought up on another forum, and seems to be little dicussed After talking to any number of people in the welding gas supply biz and out. Or even the welding biz.
What I have found out is this.
At the local outlet the people populating the store in front and back offices. Also a couple of customers, nobody had ever heard of this danger. They all looked at me like I just stepped off a saucer parked outside.To prove me wrong they called the guy that runs their acetylene plant, more on that later.
As to manifolds for oxygen and acetylene gases. Why bother as to the extra equipment you need to meet the codes for install and room for separate storage of full and MT cylinders(different rooms) along with the segregation of the types of gases.
You need a special back flash preventer Liquid type. Regulators, valves and a host of other things.
The section of the NFPA codes are 51A
NFPA 51 design and installation of oxy/act systemshttp://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=51
They aren't cheap for the sections.
Schedule 80 black iron pipe is the rule if 3/4" or less welded joint preferred.
Rex air or Rex arc is the name of a company that installs them
Copper Acetylide is chemical compound of Acetylene gas and pure copper.
Copper acetylide can form inside pipes made of copper or an alloy with high copper content, which may result in violent explosion.  This was found to be the cause of explosions in acetylene plants, and led to abandonment of copper as a construction material in such plants. Copper acetylide can be prepared by passing acetylene gas through copper(I) chloride solution in presence of ammonia:
Since it is a case of the higher the copper content in an alloy of the piping. And in general K or L type pipe/tubing or fitting is made from scrap metals rather than virgin copper. It was thought that it could be used But the current thinking is since you don't know what the alloy percentages is in it now.DO NOT USE COPPER FOR ACETYLENE GAS
I talked to the guy who runs the local welding companies acetylene plant. What he said was "just put a gun in your mouth, your loved ones will have more to bury". He has been the Smith welding supply acetylene plant operator for 25 years.
So unless you are doing so very high volume cutting and need it. It isn't worth the expense to have it done right.
As a tid bit of additional info. Silver, and mercury when combined with acetylene also form Silver acetylide, Mercury acetylide. Which are not as sensitive to heat and shock as the Copper acetylide. Which is so unstable that it generally can go kaboom as it forms under the right conditions.
I have 10 or so books on welding, only one mentions it in passing in two sentences. And then moves on to other factors for manifolds.