DCS and the Sci-Fi TV Show "Silo"

[Dan G]

Please indulge me in this bit of fun. This question is "Basic Scuba" because it mostly revolves around DCS and the effects of life in the massive 5,700 foot 144 level underground silo featured in the show "Silo." My two main wonderings revolve around DCS, movement up and down the silo, and breathing underwater from an air source that is being pumped down to the diver from the middle of the silo.

In "Deco for Divers" Powell explains how early DCS theory came from the experiences of bridge workers who would get DCS ascending the bridge cassons. In "Silo" there are porters who run up and down the silo delivering messages and goods. It occurs to me that the porters are similar to the bridge workers in the cassons other than the fact that the bridge workers were breathing air pumped down into the casson from the surface. Inhabitants of the silo are not breathing air from the surface since the outside air is deadly.

Question #1: Would the porters be subject to the same DCS risks as the workers in Powell's book or is the fact that the air is not being pumped in from the surface a mitigating factor?

The other aspect that has my curiosity piqued are two scenes where one character, Juliette, goes underwater. In both scenes, she breathes air being pumped down to her from the surface. On one dive she rigs a second stage of sorts that allows her to breathe continuously from the surface pump feeding her air. One character warns Juliette before the second dive that she needs to ascend slowly because of "the bends."

Question #2: What DCS risk does Juliette face on this 300' dive given the fact that the air she is breathing is not compressed at the same depth as she is on the dive? That being said the air is not being pumped from 1 ATA. It is being pumped from well below the surface with air that recirculates in the silo. There might be other issues , but I am ignoring those right now and focusing on DCS, because the show does try to address the issue most well known to non-divers which is DCS.

These questions are mostly done in the spirit of fun and enjoyment of a show that ventures into the world of diving, but there are a couple of interesting decompression theory and physiology questions tucked away in here. Any sci fi nerds around here want to chime in?

 

[inquis]

#1: Depends on whether the source of the water is exposed to / fed from the surface. If so, then the air in the silo must be pressurized to an equivalent depth of water equal to the distance to the surface. This is needed to keep the water from filling up the silo. In this case, porters to the outside surface would be at serious risk. (I haven't seen the show.) If not fed from outside, then there's little issue -- it'd be similar to driving up the top of a mountain in ordinary life.

#2: I can't tell if her dive is descending to 300 ft of water or just starts 300 ft below the outside surface. Either way, there's no difference from doing this at the real surface: the amount of water above her is what matters. (I'm assuming after the dive she's staying near the water surface, rather than going to the outside surface. If not, see #1.) The source of air doesn't matter, but for her to breath, it must be pressurized to something above ambient (including that at her depth). If she's diving with 300 ft of water above her, deco stops will be mandatory -- for spending 4 minutes on the bottom, she'd need more than an hour of deco without specialized deco gases. That's also ignoring the fact that breathing air with 21% oxygen at 300 ft would be fairly toxic. (If you've taken nitrox, her PO2 would be nearly 2.1 atm, well beyond today's limit of 1.4 for working dives.)

 

[Russjstewart]

Not having seen the show I can’t really picture what you are describing, but I will take a punt here,

Bridge workers got bent because the caissons they were working in were pressurised to keep the water out and after a full days work they were returned straight to the surface without decompressing , if the outside air is poisonous in the show then it is reasonable to expect the silo to be pressurised to keep the poisonous air out. Unlesss there are airlocks between different levels of the silo then the pressure inside would be rhe same regardless of what level you are on.

As there are no pressure changes within the air spaces of the silo there is no DCS risk, unless you go outside.

As for the 300’ dive it is a 300 ft dive regardless of the air source.

 

[-JD-]

If we assume that Silo air pressure is "roughly" 1ATM at the top, it should be about 1.2ATM at the bottom

Travelling up and down in the airspaces is like flying in a small, unpressurised airplane. I.e. not a problem unless you are shot from the bottom to the top. Running up is more than enough time to offgass from that trivial pressure differential.

I haven't watched the 2nd season and it has been several years since I read the book so I don't remember if the silo is significantly "over pressurized" to comtrol the water level.

If it is just natural ground water level with a nominal 1ATM airpressure , then the 300' dive, is pretty much just a 300' dive which IS a significant (de)compression risk at about 10ATM and could be accomplished with a common shop air compressor (one of mine is a 175 PSI oilless) with the risk of contaminated air.

 

[EdC]

I have watched the show (not as good as the book). The “Silo” in question has been built under the ground to a depth of approximately a mile 144 levels/40 feet per level.

I think as far as the porter question goes, the silo inhabitants in general, and the porter’s in particular, would probably have some acquired physiology to deal with the constant altitude change, similar to Sherpa’s in the Himalaya’s. That situation is somewhat believable.

The dive scenario even for someone not an expert on DCS and deco diving is a straight up death sentence. The basic premise is she is doing a hookah dive to 300 feet for something around 6-7 minutes and then has to do a CESA from that depth when her air supply is cut-off. Never mind a controlled ascent without deco stops, she was doing a panicked fast dash to the surface. If she didn’t have an embolism she definitely would have been very bent.

 

[Wibble]

The dive scenario even for someone not an expert on DCS and deco diving is a straight up death sentence. The basic premise is she is doing a hookah dive to 300 feet for something around 6-7 minutes and then has to do a CESA from that depth when her air supply is cut-off.

How long would it take to get from 90m/300ft if travelling at 10m/30ft per minute?

Ten minutes without stopping. Can anyone here hold their breath for 10 minutes?

Thankfully, superhero sci-fi actors can as the script says so ;-)

---

Just for a larf, here's the planning assuming AIR and ignoring being utterly off their tits with nitrogen narcosis that would floor an elephant!

Dec to 90m (5) Air 18m/min descent.
Level 90m 7:00 (12) Air 2.09 ppO2 **1
Asc to 36m (18) Air -9m/min ascent.
Stop at 36m 1:00 (19 elapsed minutes)
Stop at 33m 2:00 (21)
Stop at 30m 2:00 (23)
Stop at 27m 2:00 (25)
Stop at 24m 2:00 (27)
Stop at 21m 2:00 (29)
Stop at 18m 2:00 (31)
Stop at 15m 3:00 (34)
Stop at 12m 7:00 (41)
Stop at 9m 9:00 (50)
Stop at 6m 75:00 (125)
Surface at 126 minutes

OTU's this dive: 44
CNS Total: 894% **2
Gas density: 12g/l **3
Consuming 4630 litres of Air


So just under 2 hours to get to the surface from the bottom without getting bent.

However, the bend is almost the least of their worries as they would be in very serious danger of an oxygen toxicity fit [**1, **2] whilst the narcosis would be like drinking a whole bottle of whiskey [**1]; with a high work of breathing [**3]. Death is a very serious probability for this dive profile -- the sort of thing the early diving pioneers did whilst finding limits, or foolish novices who perished.

Alternatively, using the right selection of gaseS (that'll be lots of helium with hypoxic oxygen and switching to rich oxygen mixeS for decompression) would be the safe way to do that dive. Many divers on Scubaboard regularly dive deep profiles like this with little risk of injury as they plan and execute their dives on the shoulders of the giants who discovered the limits of diving safety.

 

[h2o_hamilton]

The books are so much better.

 

[Wibble]

The books are so much better.

I watched the first couple of episodes last night. Seems a familiar story from the apocalypse genre. It was recommended to me as being brilliant/amazing/really good. I'd probably describe it as trite, predictable and dull. Alas I doubt I'd bother with other episodes.

I would expect that the book version would be a lot better as there's none of the eye candy and ffffects to bore the audience. The great thing about books and audiobooks is the inner voice and descriptions leaving your own mind to build upon. A fantastic example would be 2001 A Space Odyssey where the film felt like you were in someone else's acid trip. The book was so much better and really explained what was going on.

My current favourite series has few if no ffffects, just a good story and great acting: Lessons in Chemistry.

 

[davehicks]

How long would it take to get from 90m/300ft if travelling at 10m/30ft per minute?

Ten minutes without stopping. Can anyone here hold their breath for 10 minutes?

Thankfully, superhero sci-fi actors can as the script says so ;-)

---

Just for a larf, here's the planning assuming AIR and ignoring being utterly off their tits with nitrogen narcosis that would floor an elephant!

Dec to 90m (5) Air 18m/min descent.
Level 90m 7:00 (12) Air 2.09 ppO2 **1
Asc to 36m (18) Air -9m/min ascent.
Stop at 36m 1:00 (19 elapsed minutes)
Stop at 33m 2:00 (21)
Stop at 30m 2:00 (23)
Stop at 27m 2:00 (25)
Stop at 24m 2:00 (27)
Stop at 21m 2:00 (29)
Stop at 18m 2:00 (31)
Stop at 15m 3:00 (34)
Stop at 12m 7:00 (41)
Stop at 9m 9:00 (50)
Stop at 6m 75:00 (125)
Surface at 126 minutes

OTU's this dive: 44
CNS Total: 894% **2
Gas density: 12g/l **3
Consuming 4630 litres of Air


So just under 2 hours to get to the surface from the bottom without getting bent.

However, the bend is almost the least of their worries as they would be in very serious danger of an oxygen toxicity fit [**1, **2] whilst the narcosis would be like drinking a whole bottle of whiskey [**1]; with a high work of breathing [**3]. Death is a very serious probability for this dive profile -- the sort of thing the early diving pioneers did whilst finding limits, or foolish novices who perished.

Alternatively, using the right selection of gaseS (that'll be lots of helium with hypoxic oxygen and switching to rich oxygen mixeS for decompression) would be the safe way to do that dive. Many divers on Scubaboard regularly dive deep profiles like this with little risk of injury as they plan and execute their dives on the shoulders of the giants who discovered the limits of diving safety.

The 300 foot number came from her request for 300 feet of electrical cable. Given that she was dropped 50+ feet down to the water, distance from the plug to shaft both at the bottom and top, the actual depth is going to be much less. I would guess more like 150' at most. This is not an impossible dive to do on air but is still pushing a lot of limits.

What would the deco profile above look like at 150 feet of depth?

 

[Diver-Drex]

On air and 4:30 at a 150 max depth - a direct ascent is possible. This is at GF100/100 and an ascent rate of 60fpm. Survivable but highly risky.