CS 27.861 Fire protection of structure, controls, and other parts
Each part of the structure, controls, rotor mechanism, and other parts essential to a controlled landing that would be affected by powerplant fires must be fireproof or protected so they can perform their essential functions for at least 5 minutes under any foreseeable powerplant fire conditions.
CS 27.1195 Fire detector systems
Each turbine engine-powered rotorcraft must have approved quick-acting fire detectors in numbers and locations insuring prompt detection of fire in the engine compartment which cannot be readily observed in flight by the pilot in the cockpit.
Of note - engine containment is the engine manufacturers purview.
Looking at the various media it seems the fire is from both sides? Imagine one engine had an un-contained wheel failure which would destroy the firewalls. One has stopped and you have
2 x FIRE warnings? How many buttons do you push? What does LAND IMMEDIATELY mean when you have just left the airport?
The FIRE button in the 135 will shut off the main fuel valve only. If ENG FIRE EXT is fitted the system will release when the following logic is present - an active FIRE warning, N1 < 55% and the main fuel valve is closed - from memory. You have one shot for
either engine with the standard fit.
Next time you have an engine fire keep the 5 minutes in mind.
I have seen the result of a few turbines burst over the years - two happened on the ground - B206 RRA 250 #1 Wheel shed all the blades and they went down through the engine tub, through the baggage compartment floor and onto the ground. AS350B Arriel 1 shed the PT wheel and as the aircraft was in long grass.......................not much to see. AS355 NP turbine burst at about 500' - land immediately and the TRDS was hanging by a thread.
An old instructor on a check ride once told me - if you have a fire and secured everything make a gentle turn and look over your shoulder behind you.