The concept of an oxygen/fuel fed engine is that there are extremely high temperatures created in the combustion chamber to produce the necessary energy that ultimately provides the thrust necessary for flight. On the rare occasion, fuel and ignition occur outside of the combustion chamber. In simple words, an engine fire results.
In even simpler terms, once an engine fire occurs, the basic survival of the aircraft depends entirely on extinguishing the fire. The engine fire procedures call for the pilots to shut off the fuel, the hydraulics and the electrics supply to/from the affected engine.
Once the above actions have been carried out, the pilots then activate the main fire extinguisher bottle to the affected engine. If after 30 seconds, the engine fire has not being extinguished, then the pilots will activate the back-up extinguisher bottle.
If the fire continues, the aircraft and its occupants are doomed unless the pilots can land the aircraft in a matter of a few minutes before the fire will cause structural failure and the aircraft will plummet to earth in a fiery smoky trail.
The best extinguisher known to man for aviation application at this stage in history, is Halon. Every other extinguisher agent comes a very poor second best. If aircraft manufacturers and airlines are forced to use the inferior agents by the EU or any other governing body, many fatalities will result as a direct result.
As aviators and passengers, we should all lobby for an open hunting season on "greenies", "tree-huggers" and inane politicians to try to tip the balance to bring some commonsense back into the equation of the importance human life and its continued co-existence on and the long term maintenance of this planet.