An industrial fryer is not a scaled-up restaurant appliance and it should not be protected like one. A continuous production fryer holds hundreds of gallons of oil at operating temperature, moves product through it on a conveyor, and runs for entire shifts without interruption. The quantity of hot oil involved puts it in a different severity class from a restaurant kitchen, and the process controls that keep it safe are industrial controls rather than an appliance thermostat.
The margin is narrower than it appears. Frying runs around 350 to 375 degrees Fahrenheit and fresh oil flashes somewhere above 500, which sounds like comfortable headroom. Oil degrades with use, and oxidized and polymerized oil has a materially lower flash point than the fresh product. A fryer running long oil cycles to control cost is operating with a smaller margin than the oil specification suggests, and a high-limit control failure closes it quickly.
The critical thing to understand about agent selection here is why water is not merely ineffective but actively catastrophic. Water introduced into oil above 212 degrees flashes to steam instantly and expands roughly seventeen hundred times, which ejects burning oil out of the vessel in a violent boilover. That is why NFPA 17A specifies wet chemical agents that work by saponification, reacting with the oil to form a soap layer that seals the surface and cuts oxygen while also cooling. It is a chemistry-specific solution to a hazard where the obvious agent makes things dramatically worse.