In a recent discussion regarding an accident with a Fuel-Oxy Torch system, I had some discussions about the layers of protection and the Prevent-Protect-Mitigate safety model using the Hierarchy of Controls (Elimination, Substitution, Engineering Controls, Administrative Controls, and PPE). The event did NOT involve a flash-back, but I used the flash-back requirements to demonstrate the difference in these layers of protection.
To give it away… flash-back arrestors do NOT prevent the flash-back event; they PROTECT (and some may say they MITIGATE) the event from escalating to serious consequences.
Fuel-Oxy systems require a flash-back arrestor(s) and reverse flow devices.
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1910.253(e)(3)(ii)(C)(2) Backflow protection shall be provided by an approved device that will prevent oxygen from flowing into the fuel-gas system or fuel from flowing into the oxygen system (see SF, Figures Q-1 and Q-2). 1910.253(e)(3)(ii)(C)(3) Flash-back protection shall be provided by an approved device that will prevent flame from passing into the fuel-gas system.
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To PREVENT a flash-back, we rely on ADMINISTRATIVE CONTROLS (i.e., procedures and training).
However, when those fail us, we have PASSIVE ENGINEERING CONTROLS in the “backflow” and “flame arrestor” protection devices to ensure that the system is protected from the hazards of a flash back or fuels/Oxy mixing where they are NOT intended to be mixed.