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Comment by sschueller | Hacker News Reader

This article goes a little into it but what I don't generally see in most media is explaining just how hard it is do dive at these depths. It isn't just some random guy that has had some scuba time.

The pressure alone for many is too much, then you need special mixture of air, for prolonged work you need re-breathers and a decompression chamber on board the vessel in case of an emergency.

I am also wondering how this work was performed without Norway or the US noticing it.

Edit: Sorry, I meant Sweden not Norway

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I've been to 80m depth. I have a rebreather and a couple scooters. I probably have nearly enough gear for that entire dive team. Even got some 500# lift bags.

Only thing I'm lacking are the forged passports and the explosives.

A sufficiently rich Ukrainian in the construction industry or something like that could probably have the right contacts for both of those[*].

It also probably takes less explosives than you think since the water is going to amplify the blast (pretty sure the US Navy dive manual has a good section on explosives in water and top tips like making sure that you at least get your torso out of the water if you can).

You wouldn't need a decompression chamber for those dives at that depth.

(The _Shadow Divers_ book also documents a colossal screw up on bad gas for the depth, and the hazards of going inside of wrecks at depth, which don't apply here)

> I am also wondering how this work was performed without Norway or the US noticing it.

Most things that most boats do aren't noticed by anyone. If it wasn't that way, then drug smuggling would be a whole lot harder.

[*] I'm betting Ukrainian because the pipeline wasn't benefiting them and was supplying piles of cash to their enemy, it seems kinda obvious to me.

I can't verify this, but when the story broke in Germany there were some diving experts that claimed that you can dive there in those depths without decompression chambers and that people regularly do that.

The entire discussion on what exactly you need to perform this operation has resulted in a whole bunch of contradictory opinions.

https://en.wikipedia.org/wiki/Shadow_Divers is probably worth a read if you have an interest. Basically it's about a group of hobbyist divers who explored a wreck at around that depth. They were definitely pushing the limits of amateur tech at the time, but I believe they also started using different gas mixes around then.

What I don't understand is why divers would even be needed at all. Torpedoes and depth charges are hardly new tech. If you asked me to do it, I'd just find a commodity underwater ROV for the job and strap a big bomb to it. Problem solved. It's one of the asymmetries of warfare that it's a lot easier to destroy stuff than to build it.

That’s probably a far more traceable operation using those approaches though.

the need for decompression (and the required decompression time) is very much dependent on the duration of the dive (i.e. how much gas is dissolved into your blood depends on how much time your blood was fed gases at higher pressure). If your dive is just a quick down,drop some stuff, and back up right away (especially with a gas mixture optimized for depth)… then yeah, you might be able to do it without decompression…

…whereas if you stay an hour or two down there, giving a long enough time for the gases to reach their high pressure solubility levels, you better not get back up without decompression.

Open Circuit dive to 80m with 15 mins of working bottom time (CCR would cut total runtime down to 85 mins and slash the helium bill). I ran it with Nominal conservatism since I figure we're talking about people crazy enough to play around with explosives. You can likely cut off of half the O2 stop and as long as you pass your saving throwing against type I DCS and don't have a PFO you'll likely be fine for 4 dives. I would assume these people would wind up pushing the tables exceedingly hard.

  V-Planner 3.105 by R. Hemingway,
  VPM code by Erik C. Baker.

  Decompression model:  VPM - B

  DIVE PLAN
  Surface interval = 5 day 0 hr 0 min.
  Elevation = 0m
  Conservatism = Nominal

  Dec to 80m  (4) Trimix 15/55 18m/min descent.
  Level 80m  15:33 (20) Trimix 15/55 1.34  ppO2,  24m ead,  30m end
  Asc to 54m  (23) Trimix 15/55 -8m/min ascent.
  Stop at 54m   0:45 (24) Trimix 15/55 0.95  ppO2,  14m ead,  19m end
  Stop at 51m   1:00 (25) Trimix 15/55 0.91  ppO2,  13m ead,  17m end
  Stop at 48m   1:00 (26) Trimix 15/55 0.86  ppO2,  12m ead,  16m end
  Stop at 45m   1:00 (27) Trimix 15/55 0.82  ppO2,  11m ead,  15m end
  Stop at 42m   1:00 (28) Trimix 15/55 0.78  ppO2,  10m ead,  13m end
  Stop at 39m   1:00 (29) Trimix 15/55 0.73  ppO2,  9m ead,  12m end
  Stop at 36m   2:00 (31) Trimix 15/55 0.69  ppO2,  7m ead,  11m end
  Stop at 33m   2:00 (33) Trimix 15/55 0.64  ppO2,  6m ead,  9m end
  Stop at 30m   3:00 (36) Trimix 15/55 0.60  ppO2,  5m ead,  8m end
  Stop at 27m   3:00 (39) Trimix 15/55 0.55  ppO2,  4m ead,  7m end
  Stop at 24m   4:00 (43) Trimix 15/55 0.51  ppO2,  3m ead,  5m end
  Stop at 21m   3:00 (46) Nitrox 50 1.54  ppO2,  10m ead
  Stop at 18m   3:00 (49) Nitrox 50 1.39  ppO2,  8m ead
  Stop at 15m   4:00 (53) Nitrox 50 1.24  ppO2,  6m ead
  Stop at 12m   5:00 (58) Nitrox 50 1.10  ppO2,  4m ead
  Stop at 9m   8:00 (66) Nitrox 50 0.95  ppO2,  2m ead
  Stop at 6m  10:00 (76) Oxygen 1.60  ppO2,  0m ead
  Stop at 3m  16:00 (92) Oxygen 1.30  ppO2,  0m ead
  Surface   (92) Oxygen -6m/min ascent.

  Off gassing starts at  62.2m

  OTU's this dive: 110
  CNS Total: 53.2%
  Gas density: 5.7g/l

  183.8 cu ft  Trimix 15/55
  32.0 cu ft  Nitrox 50
  21.9 cu ft  Oxygen
  237.8 cu ft  TOTAL


  DIVE PLAN COMPLETE

  *********   WARNING & DISCLAIMER  *********
  This V-Planner generated dive schedule could indirectly kill you.
  The author does not warrant that it accurately reflects the Varying
  Permeability Model algorithms, that it won't get you bent or dead, or that it
  will produce safe, reliable results.  This dive schedule is experimental
  and you use it at your own risk.  Diving in general is fraught with
  risk, and decompression diving adds significantly more risk.
  Deep diving utilizing multiple gasses, including Helium, is about
  as risky as it gets.

  This schedule is not intended for uneducated users. V-Planner and the
  decompression schedules it produces are tools for experienced mixed-gas
  decompression divers ONLY.  If you have not been properly trained in
  mixed-gas decompression diving by an internationally recognized technical
  certification agency and/or don't have a firm handle on decompression
  planning and mixed-gas diving, then DO NOT USE THIS DIVE SCHEDULE.

The article literally does describe how divers would do so with quotes from a subject matter expert:

>Achim Schlöffel, a German extreme diver who runs a diving school and helps companies protect vessels and underwater installations from sabotage, said explosives could have been planted by a group of well-trained technical divers accustomed to working at such depths—around 80 meters—assuming they had several days to do so.

>Six divers, he said, could have lowered the explosives in several dives using commercially available equipment such as underwater scooters or propulsion vehicles, airlifting bags and buoys, and a portable sonar. “I know dozens of professional divers who would be up to the task,” Mr. Schlöffel said.

The sea is big and has many innocuous boats, anything happening under water is effectively invisible.

And you're assuming they actually went all the way down; someone else mentioned an ROV, but if you know where the pipeline is you can probably sink explosives on a weight too. It doesn't have to be accurate, not when the pipe will collapse and be contaminated with little encouragement.

Why should Norway of all countries notice it if it was happening within Swedish and Danish waters?

And how to expect a Navy/Army/Air-force to notice and study in detail what every little boat is doing. And even more difficult to notice what a diver or two are doing.

You assume the bomb was placed, and not dropped with weight or with underwater "drone"[0](Hilarious). 80 meters is probably not too deep for Sonar/Lidar for spotting the pipe, Xprize Ocean discovery comes to mind. In addition top free diver athletes do dive for 80+ meters[1].

[0] https://www.youtube.com/watch?v=FwIWG5_rgC0 [1] https://www.youtube.com/watch?v=aV2kBfhqkGk

The world’s best free diver did a 214m dive with a weighted sled and buoyancy device. Scuba may make it more complicated in this case if all they were doing was attaching an item.

How deep do they need to go? How close do they need to be? Let's not make this more complicated than it needs to be.

Since we're well into speculation mode here, try this: footage of the aftermath[0] reveals an enormous 50-meter hole in the pipe, which was made of pretty thick metal. I suppose it would have to be, to carry gas under pressure from within as well as withstand being kept empty, as it was at the time of the explosion, under pressure from without.

How big does an explosive have to be to cause that much damage? Pretty big, I think. Big and heavy.

How close does an explosive that big have to be? Not very close, I think.

Of course, there's a trade-off! The close it is, the less big it has to be and the farther it is, the smaller it can be. But a 50-meter is much bigger than it needed to be to disable the pipeline. It is almost as if the people dropping the bomb couldn't be sure how close they would get with it, so built a big enough bomb to ensure rupturing it whether it landed directly on top of it or a number of meters away. Maybe they got lucky, and expected a smaller hole. Maybe they got unlucky and expected a bigger one.

I mean, the BBC footage involved zero people getting in the water. They just went to the area and dropped in a camera on a long cable and navigated to the hole.

It's possible that nobody even got in the water for the bombing. They could have used a "fish finder" to make sure they were pretty close to the pipe, and even drop a test object to see how the underwater currents might shift it, but it was a pretty big bomb, I think it probably mostly went straight down. Close enough for a big bomb to make a hole in a big pipe, anyway.

0. https://www.bbc.com/news/world-europe-63297085

I guess there might be a crater visible on the seabed if that was the case. Or maybe it was all scoured clean by the subsequent gas leak?

There was no big gas leak, the pipeline had already been shut down by the Russians a week or so prior.

The closed pipelines contained gas.

The pipeline is kept full and under pressure even when not delivering gas. It was one of the worst environmental disasters but it's being ignored because of controversy of who blew it up.

The pipe has a thick layer of concrete around it. I think you would need some sort directional charge.

A large creator can also occur when the pipe burst from the pressure inside even if punctured by just a small hole.

No need for a test object. Just drop the bomb in the water with a tether. Don't like where it landed? Pull it up and try again

Why would Norway in particular notice? The explosions occurred closest to Denmark and Sweden.

80-110m is not such a deep dive, I personally know at least 3 SCUBA divers that have taken classes and dived to 100m, it's something that amateur divers can do with enough resources.

I don't dive but 80 meters doesn't sound like much especially for what is purported to be clandestine and independent agents that are clearly motivated and accept the risk. Shit- people are willing to strap explosives to their bodies for the right cause. The pipelines were not all cleanly severed either. Did they even need to dive in order to drop charges near these pipes?

There was an NPR article that had some quotes about the difficulty in pulling off such an operation successfully. The assumption by investigators was these had to be people with specialized expertise. That would seem to limit the number of people who could pull this off.

But every country probably has some of those people and the equipment needed. So it doesn't really bring us closer to figuring out whodunit.

I think if you had a list of suspects, people in the area… if they could do the thing, you’re probably onto something.

They could have used an ROV.

Eighty meters is within range of commercial ROVs and even consumer ROVs.

https://www.deeptrekker.com

https://geneinno.us/

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