I was just pondering as an ex marine engineer, about the latest Cruise liner to be stricken down at sea with a loss of propulsion and main electrical power.
I’ll describe the propulsion system of my last ship, which although not being a cruise liner, due to it having GUNS and things, had the same basic principle of propulsion and power generation.
Our main source of power was 4 x 4.7 Mw, 6.6kv (6,600 volts), diesel generators. Now 6.6kv voltage is something you have to be really scared about. A small error can submit you to a lethal mini lightning bolt, that will fry you in instant.
These diesel generators have a fuel injection system that supplies fuel to the cylinders at approximately 300 bar (dependant on engine manufacturer). A loose connection, or a split in the pipework can result in a high pressure mist that could impinge on a hot exhaust. Here again I’m speculating as normally the high pressure systems are normally shrouded.
Anyway lets suppose that’s the cause of the fire in the engine room. The first thing that the control room staff would have had warning of this would normally a leakage alarm, rapidly followed by Flame flicker and smoke alarms. Some confusion can occur if the staff check the CCTV cameras, and delay action. I was on one ship where there was a fire in a machinery space, where the engineers entered the control room, looked at the CCTV monitor, saw no picture, and concluded that the camera was defective. In fact it was because the smoke was so dense the camera couldn’t operate. (That was only 90 seconds from the smoke detector operating).
Anyhoo, I digress.
How do you fight a fire when the equipment has such high voltage? The last thing you’re going to do is attack a 6.6kV generator with a saltwater fire hose. you’d be a dead, smouldering corpse, within seconds. ( remember the lightning bolt).
The answer is to inject the machinery space with an oxygen denying gas such as CO2 or Halon. This will hopefully starve the fire of oxygen and result in a non fire position. However it takes a short while to shut down the other generators in a safe manner as many commercial generator take their air supply direct from the machinery space. The last thing you want to happen is the diesel sucking the smothering gas in and then consequently chucking it up the funnel to the outside.
I hope you’re not getting bored.
Whilst the generators are being shut down a team needs to be shutting down all flaps and openings to the machinery space in order that the smothering gas is not going to be dispersed. Time is of the essence.
Once the gas has been released it should extinguish the flames, but will not cool the space significantly. It then becomes a waiting game for the space to cool down to a safe level to allow re-entry without re-ignition of any hotspots caused by air from the re-entry.
One unfortunate side effect is that you’ve lost all your electrical power and the lights have gone off and your fire pumps have stopped. Oh dear.
However, help is at hand. All ships have an emergency generator that will start automatically and supply limited power. This includes supplying limited lighting (usually 50%), power to an external fire pump, steering gear, navigation lights, and radio equipment.
Monitoring of the boundaries should continue until three consecutive drops in temperature of the machinery space, before any attempt to enter. This can take 24 hours, to be sure it is safe to re-enter.
This gives you time to make sure your firefighters are rested and in a good state. This includes getting a plan for re-entry in a safe manner, and sorting out your logistics. I.E, All breathing apparatus fully charged, enough hoses, considering that entry ladders may have melted or distorted, lack of lighting, etc.
Re-entry. There must be enough length of fire hose to enable the team to reach the furthest reaches of the compartment in case of a flare up. If not you might have made matters worse.
The happy ending: You have recovered the machinery space.
THE END
Maybe I’ll write a post of the trials and tribulations of attending the firefighting and damage control course at HMS Phoenix.
Sleep well and don’t have nightmares as you cruise the seven seas. (I’m still alive after 43 years. A great many of those years as Officer in Charge of the Fire and repair party, on a number of ships).
