IRC the LP cock could be closed by the Fire handle or the LP switch on the F/E panel.
The BOAC initial drill was -
1. Thrust lever closed- to avoid shutting off the wrong motor.
2. Start lever cut off- hp valve at the engine
3. Fire Switch (handle) pull- trips the genny, shuts the hyd pump supply off, closes the lp cock(if IRC also the hp electrically) and arms the extinguisher cct.
4. Fire off the first extinguisher if the fire still evident or a fire warning.
5. 30 secs, fire off the second shot and if no joy speed up to get the fire to leave the scene. Great idea but we believed Boeing at the time!
F/E then announces phase one complete and reads the check list aloud to double check all is done.
Later on, cant remember when, he then switches off the LP cock switch on his panel (this should do nothing as it was already closed but it was belt and braces)and announces light on dim. The valve had a blue light. Bright for transit, dim for closed. Push to test dim produced a bright light thus checking the bulb was ok and the valve closed.
This is all 30 year old memory but as a trainer I seem to remember this still-sad git!
It could be that WE was not modified as my history only goes back to 1970.
Straightfeed