My memory is a victim of age but this is what I was looking for:
https://www.google.co.nz/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwilg4XEuu71AhX7yjgGHXzrBGEQFnoECAcQAQ&url=https%3A%2F%2Fassets.publishing.service.gov.uk%2Fmedia%2F547c704be5274a4290000089%2FMaerskDohaReport.pdf&usg=AOvVaw3OZNXmU1c-mKrbDmFwi-Gt
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They’re not assumptions. They’re the result of both personal direct experience and critical thought about stack fires.
Go put a vacuum gauge on an exhaust system that just suffered a stack fire and tell me what you find. One shouldn’t immediately treat a shipboard fire like a physics problem. You can, but you need to ensure you actually have all the variables before you attempt to solve the problem, just like with a stability issue. Otherwise you just risk making it way worse.
There’s obviously sufficient oxygen to maintain combustion in a stack fire. But that oxygen flow is controlled and lessened by combustion gases. The running engine contributes heat, but the exhaust flow also directs heat out of the stack. Shutting the engine down risks a rapid increase of oxygen to the fire which can make the problem become unmanageable, while simultaneously eliminating the cooling effect of the exhaust carrying heat with it out of the stack.
Starving the fire of oxygen is actually making an assumption that you still have enough integrity in the system to actually do that. If you’ve ever attempted to trace down vacuum leaks in a system that wasn’t just on fire, you have an idea of how difficult that can be. Now add the expansion of a fire of unknown location and extent, insulation, etc, and you have a problem you can’t possibly solve. Even with CO2 injection available you don’t want to shut the engine down until you have the ship ready to fight a fire.
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I’m very skeptical on the fire hot enough to turn water into fuel scenario…seems like if that were true, the world’s energy problem would be solved.
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Where does the additional oxygen come from when the engine stops spinning and stops being an air pump that pumps air from engine inlet to exhaust stack?
There is the small problem of getting to over 1000 degrees Celsius to kick the reaction off.
One of Horizon’s (then SeaLand) D7’s had a stack fire that turned into a hydrogen fire quite a few years ago. The entire economizer burned and became a pile of slag. Don’t to blow tubes when you have a stack fire.
How can one prove that water turned to hydrogen? Do people not take basic high school chemistry and learn what a covalent bond is? Again, wouldn’t this combustible water solve all of our energy problems and we could ditch the wind turbines and electric cars?
You know what seems more likely??? The steel got so hot that it in fact became the fuel. combustion temperature of Iron? - Metal and Metallurgy engineering - Eng-Tips
The ignition temperature of steel occurs when its color is cherry red and its temperature is about 1300°F to 1400°F (704°C to 760°C).
14.1 The Heat of Combustion of Steel - Halverson CTS
In thermolysis, water molecules split into their atomic components hydrogen and oxygen. For example, at 2200 °C about three percent of all H2O are dissociated into various combinations of hydrogen and oxygen atoms, mostly H, H2, O, O2, and OH. Other reaction products like H2O2 or HO2 remain minor. At the very high temperature of 3000 °C more than half of the water molecules are decomposed, but at ambient temperatures only one molecule in 100 trillion dissociates by the effect of heat.[15] The high temperatures and material constraints have limited the applications of this approach.
Well shoot, this is an interesting topic. Mostly because it can bring together those who have read about it with those who have seen it. Personally I appreciate @MAK ’s input as I would have thought “shut engine down” would have been step one, without more thought. It still might be the right answer, but I value the extra discussion. And I think that discussion about shipboard fires should happen more often than a 5-year AFF Reval where maybe someone speaks up.
I’ve had shipboard fires, but stack fires? Not personally. I’ve had a console fire, HV converter fire, AC Compressor motor fire, Exhaust bank insulation fire, Generator coupling failure smoke-show, Generator crank-case explosion, and arguably the worst: Helicopter crash fire with burning jet fuel on top of accommodations and multiple casualties, injuries, fatality.
As for stack fires, I’ve only had the fall-out/recovery from an aux steam generator stack fire, on a motor vessel. I know what the response was, but I wasn’t there. I know what the missed fire indications were, but I wasn’t there. So for anyone who has responded to a stack fire, I’ll listen. I’m curious. What worked? Do you ever drill for it? Do you know where your stack covers are? Is anyone willing and prepared to climb the stack with a fire hose? Thats what my shipmates did. Water down the hole. I’m not sure that would lead to the best recovery time on a Main Engine stack, dumping sea water down to collect near a hot turbo compressor blade.
But I can’t for the life of me think of a CG Exam question that covers this, or an STCW course scenario that covers this. So for anyone who’s dealt with a stack fire, steam or motor, please do tell…
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Reading the report on the Maersk Doha when one fire hose was directed down the stack the temperature climbed because they were adding fuel in the form of water. That is why copious amounts of water are required all at once to drop the heat below 1000 degrees Celsius.
Of the ships that I was involved with the superheat steam temperature was 454 degrees Celsius so we were almost half way there.
My last steam ship a ULCC in 1974 had two Kawasaki roof fired boilers but of the detail I can’t remember.
How did they measure the temperature increase? Did it just suddenly feel hotter where they were standing?
A lot of that water turning to steam most likely became a medium for transferring heat from burning soot to any metal it contacted. Since it takes well above 2000 degrees C to break down even the smallest weight of water into an insignificant amount of gaseous O2 and H2 the idea that that gave the fire a boost is hardly likely.
The heat it takes to change water to steam comes from the fire and the hot metal, that heat cools the fire and the metal, it makes hot “steam” that carries way more heat away than just air or engine exhaust. Anyone in the vicinity will think that it suddenly got hotter but in fact the fire and the metal got a lot cooler.
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This is from Annexes D of the report @Hogsnort has linked to.
Here’s the chemical reactions:
Here’s the photo:
My understanding is the disassociation of water allows the oxygen from the H2O to react with the iron (Fe).
A bunch of melted tubes doesn’t prove much other than it got hot enough to melt steel.
Steel is combustible, we see that every day when someone is using an oxy fuel cutting torch. The metal is preheated by the flame until it reaches a relatively low temperature of 7 or 800C then a very large dose of O2 fuels the combustion and blows the slag away. The heat of combustion of the steel itself is the major contributor of heat from that point.
A soot fire is easily capable of exceeding the temperature required to melt steel and the flow of oxygen rich exhaust from a lightly loaded diesel fans the flames and pretty soon you have what is shown in the photo.
If you look at the amount of heat required to disassociate enough water to maintain much less increase the combustion of steel it should be apparent that the numbers don’t balance.
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Had a couple. Ignition was probably from the load being put on the engines. Shutting them down wasn’t an option. At one point a six foot blue flame shot from the top of the stack. We used small amounts of water on the exterior to control heat. When the flames died to orange colors and got smaller, a metal can was used to smother the fire.
Had a couple flue fires from a wood stove on shore. One we hit hard with water. The soot detached from the flue and fell down into the house. After that we just tended the heat and let it burn.
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There are standards for the steel to be used in exhaust stacks. ASTM specifies the quality of steel to be used depending upon fuel, velocity etc. Whether the standards are followed depends on the shipbuilder and class oversight. The last stack fire I witnessed was a medium speed diesel vessel that spent a lot of time shifting position at low load conditions. The vessel was leaving port when the fire started. The captain called down and asked if he should shut the engine down. I suggested he muster the fire crew to monitor stack boundary spaces and but put NO water on the stack. Otherwise run the engine as close to 100% as was prudent considering navigation requirements. The fire exhausted itself of fuel and thankfully the stack was of good material. Somewhere I have photos of the fireworks we left in our wake.It was exciting and educational.
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keerimany!!! … shipengr!, had some fires huh? i think i may avoid your ships, !!
MAC did what I did, for a stack fire I’d MAYBE slow the engine reducing heat output and keeping the co2 in there, Ships I sailed you’d NOT want to pour water in there (wth?) for you’d be out a engine or two. (evidently this refers to a diff exhaust))
I thought you meant a fire in the fidley which shouldn’t burn a lot more than someone’s drying clothes. I just let it burn, but yea, it’s something you’d rather happen on the mid-watch (ha ha) and probably does since he was reading a book anyway !!
I think there’s two concepts that need to be separated here:
One is the idea of water splitting into hydrogen and oxygen, burning back into water, and causing a net energy gain in the process. Once you stop to think about it, this is pretty nonsensical, regardless of how high of a temperature is present. If that could occur, every lightning strike on the ocean would set it on fire, to say nothing of the times we’ve nuked it!
The other is the idea of an exothermic reaction when water is applied to a very hot iron surface covered in carbon and other goodies. This one seems fairly straightforward to anyone who’s ever encountered rust. The only question would be whether the reaction between water, iron, and air is more exothermic than the reaction between iron and air alone.
I’d love to see a detailed analysis by someone with a few degrees in chemistry and/or a really well designed experiment to figure out what exactly is going on during these very hot fires. I think the takeaway for now is that water sometimes makes things worse, but the way we describe that interaction doesn’t necessarily reflect what’s really going on
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Well reasoned but the lightening strike on the sea the heat is almost instantly absorbed. We used to use ozone generators to sanitise ships holds before loading frozen meat so I recognise the smell and I’ve smelt ozone in a near lightning strike on the water so there was definitely some reaction. I have experienced some fires at sea but fortunately I have managed to give a stack fire a swerve.
No argument against a reaction, what I was saying is that the reaction can’t be self-sustaining unless there’s other types of molecules involved. As you pointed out, the initial energy is diminished by the reaction instead of growing. There’s no way to gain energy just from breaking the bonds and then re-forming identical ones
I’ve never worked on a slow speed plant that had a means to seal the stack. I’ve also never worked a propulsion plant that had a fire suppression system for the stack. I supposed you could dump the scav box fire CO2, but that’s usually just a couple of HP bottles and I don’t think it would be very effective and it would take some time to employ, particularly on modern 2 strokes with hydraulically actuated valves.
Also, my experience lately has been that water washing the economizer tubes of some waste heat boiler designs has fallen by the wayside. I think it’s more common on newer vessels to use soot remover chemicals for cleaning tubes.
I’ve also noticed the lack of water washing, some ships seem to water wash only very infrequently and never use chemicals either, without any ill results. Entering the economizer for inspection doesn’t really seem to show much buildup and the steam production doesn’t drop off either. I wish I understood the design of these systems better.