This is a subject that comes up from time to time and has created some very passionate discussions, and what I’m about to write is probably going to start even more temper tantrums LOL!
First of all, what is a flashback? A flashback is where the fuel gas ignites inside the torch before it is expelled from the mixing chamber. 98% of all flashbacks are going to occur on pre-mix torches. You will know you’ve had a flashback when you hear a loud POP, sometimes a SNAP, occasionally a BANG. This is the mixture of fuel gas and oxygen preigniting inside the mixing chamber. The cause for concern is that this ignition can then travel back down the fuel gas line and cause an explosion at the regulator.
Here are my personal thoughts on flashback arrestors (FBA’s):
1) First and foremost, if you want to use them, or you are required to use them for whatever reason, by all means do so. Disregard everything else written below.
2) If you are using a pre-mix torch (even a pre-mix with a surface mix), FBA’s are required, hands down, no further discussion. The FBA’s need to be installed as near to the torch as possible on both the fuel gas and oxygen line. If you are using a concentrator, then just use one on the fuel gas side. This is double important if you are using natural gas — a flashback on a natural gas line would be catastrophic.
3) If you are using a surface mix torch: here is where things get contentious and more than a bit murky. I personally believe that FBA’s on surface mix torches are unnecessary, as the fuel and oxygen mix outside the body of the torch (hence the name “surface mix”). It takes a very unlikely set of circumstances in order to cause a pre-mix condition in a surface mix torch, and I believe that the chances of those circumstances happening are very unlikely in normal glassworking environments. This is not to say that you should not use them however. They do add a certain measure of safety to your operation, and if that additional level of safety is important to you, then by all means, use FBA’s on your torches.
FBA’s should be used in pairs, one on the fuel gas and one on the oxygen (unless you are using a medical concentrator or industrial oxygen generator, in which case you should only use the fuel gas FBA).
FBA’s are known to fail and cause gas flow problems. If you suddenly start having flow problems, remove the FBA from the lines and check your flows again. If you have proper gas flow, then the FBA needs to be replaced.