Hose to torch or hose to regulator?
Dale gets it right this time with this answer:
Torch to hose protects hose and regulator. Hose to regulator only protects regulator.
But from out of left field comes this answer from Malcolm at ArtCo:
If something were to burn/cut/puncture the hose, having the flashback arrestor between the torch and the hose won’t protect you, the regulator, or your tanks!
My opinion is that you should have one at the regulator.
You *may* use two arrestors: one at the torch, and one at the regulator. But, I don’t think that it is necessary.
First of all, what IS a flashback? Simply stated, a flashback is the flame travelling backwards through the torch into the hose. Since the flame starts at the torch face, it makes sense that the flashback arrestor be put as close to the torch as possible.
A cut/burn/puncture of the hose will indeed cause an additional fire, but because of the pressure of fuel surging out of the hose, a flashback will not occur, since the flame is already outside the the hose.
Surface mix torches are highly unlikely to flashback, although there have been a couple of documented incidents where this has happened. Pre-mix torches are far more likely to flash back, and these types of torches should ALWAYS have a flashback arrestor installed at the torch.
The flashback arrestor is a safety device, and like all safety devices, is designed to perform a certain task to protect the user and equipment. It is my opinion that they really aren’t necessary for surface mix torches, but are REQUIRED for pre-mix torches. There may be issues with their usage that you should be aware — some flashback arrestors do affect line pressure, and some require a certain pressure in the line in order to operate properly. If you run your torch at low pressure, under 3 PSI for examply, your flashback arrestor may actually not allow gas to flow to your torch!
Additionally, if you are using natural gas at household pressures (1/4 to 1/3 PSI) flashback arrestors will not function at all and should not be used.