Originally Posted by
Wirbelsturm
You are correct but it is important to differentiate what these controls do.
The cutoff switches close ONLY the fuel valves whereas the fire handles cut off the spar valves and fuel valves, trip the engine generators, closes the bleed valves, isolate the hydraulics, depressurizes the associated engine driven pump and removes power to the thrust reverser isolation valve.
Not true - Boeing design practice is that the fuel cutoff switch commands
both the engine fuel valve and the spar valve - just like the fire handle - just via different wire routing paths.
All current production Boeing aircraft shut both the engine and spar valves when the fuel switch is placed to Cutoff.
The primary reason that the pilot is instructed to set the fuel switch to Cutoff
before pulling the fire handle is redundancy - when the Fire handle is pulled, it removes power from the fuel switch circuit. If there has been damage to the fire handle wire routing but not the fuel switch wires and you pull the fire handle first, you've lost the ability shutoff the fuel. Fuel switch first maximizes the ability to shutoff the fuel after a major failure.