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IphtashuFitz t1_j6jxytj wrote

Reply to comment by bostonvikinguc in Massive ship in the harbor this morning by NAFAL44

Back before 9/11 they didn't bother shutting anything down, they'd just warn boaters over VHF that it was inbound, and they'd send a couple USCG patrol boats to escort it and shoo other boats out of its way. I crewed on some USCG Auxiliary escorts back in the 90's and it was crazy how many sailboats thought they had the right of way over that thing and other big cargo ships. I bet the skippers on these things love having the harbor shut down these days.

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bostonvikinguc t1_j6jy4qe wrote

That big tub is slow. It’s also terrifying to think how much damage could be done if it was to pop

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IphtashuFitz t1_j6k0e6x wrote

I saw an article years ago that indicated that the danger of such an incident is seriously overblown. I forget the specifics, but it said that LNG requires a LOT of oxygen to become explosive, and a leak, etc. in the open is likely to dissipate the gas long before it reaches an explosive mix. The more likely scenario would be a fire that burns the fuel off. While that would severely damage the ship itself, as long as the fire was contained to the ship it could just slowly burn itself out with no significant damage to the surroundings.

Think of it being similar to lighting a bucket of gasoline on fire versus what happens when it's the vapors from gasoline that ignite.

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RufusTCuthbert t1_j6kfdx6 wrote

The LNG tankers are more dangerous empty (fumes) than full (when it’s full of what is essentially gas jelly).

IIRC (and not sure if it’s still the case) they used to have to time the LNG ships so that the tide was just right; if it was too high it would not clear the Tobin, and if it was too low there was a possibility of the ships crashing the harbor tunnels.

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bostonvikinguc t1_j6k3j5z wrote

More concerned about a car going over the top off the bridge.

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Hribunos t1_j6meiqo wrote

Sure, the LNG probably wouldn't detonate (not enough O2 like you said- it would burn but it would burn relatively "slowly") but if the hull on one of those ships ever failed you would get a wave of cryogenic liquid washing ashore. It would do a lot of damage from freezing. And then catching on fire.

No boom, still a big problem.

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dyqik t1_j6p34o3 wrote

It wouldn't stay frozen or have much ability to freeze anything for long - the ocean is big [citation needed] and cryogenic liquids really don't have a lot of heat capacity compared to water.

Freezing stuff also usually doesn't damage much, unless there's water to expand inside it.

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Hribunos t1_j6pfqs9 wrote

Have you ever seen LN2 skittering across a floor? It's like that. There wouldn't actually be that much heat transfer from the ocean- the LNG would skate across the surface on a thin layer of vapor.

I used to work in the seaport, and we ran the numbers - it's not enough to destroy building or whatever but anyone standing on the pier is gonna be a popsicle.

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dyqik t1_j6pgjcm wrote

I build cryostats and operate superconducting detectors - I've been handling liquid cryogens for over twenty years.

I've stuck my hand in liquid nitrogen hundreds of times.

The main danger from liquid cryogens is the displacement of oxygen from the area when it flash boils.

While small amounts of liquid will skate around on a vapor barrier (leidenfrost effect on solid surfaces), in volume, the boiling at the interface between water and the liquid will produce some amount of turbulence and mixing that increases heat transfer.

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