Karl Denninger wrote:

Halon won't shut a diesel down at all. It will simply burn the Halon and
contaminate the oil while producing the phosgene. The Halon (and its later
cousins) manufacturers are well-aware of this which is why they require
an electrical shutdown system to be installed for Halon bottles on boats
with Diesel engines.

Misleading. Halon will not burn, the engine will not burn halon.

Engine rooms fitted with CO2 flooding systems also require that all
ventilation be secured and the engines stopped before releasing the gas.
These are fire extinguishing systems, not emergency diesel engine
shutdown systems.

The reason for an engine shutdown system in engine rooms fitted with a
fixed halon extinguishing system is due to the fact that the quantity of
halon available is calculated to provide a 5 percent concentration of
halon when discharged. The system should include a timer that allows for
the engine to stop before the gas is released or prevent its release
while the engine is still running. Because the halon gas mixes with the
atmosphere rather than displacing it as CO2 does there is still enough
O2 remaining in the atmosphere of the flooded space to support life and
allow a diesel to run.

This 5 percent concentration is sufficient to prevent the chemical
reaction we call fire without killing people in the space. The engine
will still run long enough on a 5 percent concentration to completely
remove all halon and therefore prevent the system from extinguishing a
fire. The required shutdown system is to insure that the space remains
at the required concentration.

If you have enough halon, such as in the form of a large portable
extinguisher like a CO2 unit, it will shut down the engine just as CO2
will. If you have an equal size supply of halon as CO2 and apply it
directly to the engine air intake just as you would CO2 it will stop the
engine with equal certainty as CO2.

Rick