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In the book Ship Breaker by Paolo Bacigalupi, one of the characters falls into crude oil and state that one cannot swim in crude oil. The character can swim in water.

If true, why would you not be able to swim in crude oil?

  • Does the character state that they can't swim because of them being in crude oil? – Andrew Grimm Feb 13 '13 at 9:42
  • @AndrewGrimm: Thanks! I can now see how my question was unclear. Does the edit help? – Sardathrion Feb 13 '13 at 9:45
  • with the density of crude oil between 0.8-1.0 kg/l, a person with weight of 70 kg (desity around 1.0) would have to "swim out" up to 14 kg. – bummi Feb 13 '13 at 10:14
  • There should be a spoiler alert! I didn't read that book yet. – Duralumin Feb 13 '13 at 10:41
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    @Duralumin: Yeah, okay, you got me there. However, it happens in very early in the book, is not foreshadowed, and you do not know which character or whether they survive or not. ^_~ – Sardathrion Feb 13 '13 at 11:12
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Density and Buoyancy

Density of Fluids

Dead Sea†                    1240 kg/m3
Sea Water                    1025 kg/m3
Water                        1000 kg/m3
Crude oil, Mexican            973 kg/m3
Crude oil, 48° API            790 kg/m3

The Human body has an average density of 1062 kg/m3 ‡ This is why (most) humans float in the Dead Sea without any swimming effort and do not sink.

Lighter forms of crude oil would support the human body less, this can make staying afloat difficult or impossible.

Buoyancy depends on the weight of the volume of displaced fluid compared to the weight of the object displacing the fluid. To stay afloat you have to provide a swimming force that is equal to the force of gravity on the mass difference. The greater the deficit in density, the greater force you have to provide, at some point this force exceeds that which a human can provide for any significant time.

Oxygen

Lighter forms of crude oil should have a greater proportion of volatile hydrocarbons. The vapours of these hydrocarbons will displace air at the surface of the oil and make it difficult or impossible to obtain oxygen by breathing.

Reports

In general, oil on seawater (for example) quickly spreads into a thin film, so buoyance may not be an issue. But the difficulties in swimming and breathing can be potentially fatal

Man rescued from drowning in China oil spill

Engineer drowns in crude oil storage tank


Wikipedia:Dead Sea
Wikipedia:Orders of Magnitude

  • OK for the theory, but in practice? – Sklivvz Feb 13 '13 at 10:40
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    For practice, you should first find someone who is going to let you fill his swimming pool with crude oil. – Duralumin Feb 13 '13 at 10:44
  • "at some point this force exceeds that which a human can provide" I'd +1 this answer if you were to include figures on whether a typical human swimmer could provide that additional force (could an Olympic gold-medallist?). – Ian Feb 13 '13 at 10:51
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    @Suma: I agree, there are numerous complications like density and viscosity that affect efficiency as well as numerous biological factors such as the varying rates at which the body can convert different types of energy store within the body, supply oxygen to the muscles and carry away metabolic wastes. A simple numerical analysis may be pointless. – RedGrittyBrick Feb 13 '13 at 14:05
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    I'm not sure the complications are relevant. The bottom line is that bodies (just about) float in water because they are slightly less dense, but they will sink in most oils as they will be significantly more dense. – matt_black Feb 14 '13 at 16:32
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To followup a comment to RedGrittyBrick's question:

I'd +1 this answer if you were to include figures on whether a typical human swimmer could provide that additional force (could an Olympic gold-medallist?).

Per RedGrittyBrick's reference data the density of crude oil varies from 0.79 to 0.97. The second-highest density of all the oils listed is 0.915.

The density of fit young man is about 1.08 (very close to 1). A 70kg man swimming in oil whose density is 0.915 would therefore experience negative buoyancy of about (1 - 0.915) x 70 = 6 kg.

This weight increases to 12 kg if you choose the 2nd-lightest crude (density 0.825) instead of the 2nd-heaviest.

These numbers imply that it would be like swimming in water with a 6..12 kg weight attached, which may be feasible for some but is not easy: Lifeguard Certification FAQs says that the hardest part of the test to become a lifeguard is the lifting a 10 pound (approx 4.4 kg) brick.

The amount of swim force you could theoretically (assuming for example that you can breathe in the fumes) generate is IMO slightly greater in oil than water, because oil has a higher kinetic viscosity ... but not very much more: approximately 50 SSU for crude compared with 38 SSU for water.

A simple numerical analysis, to @Sklivvz's pont, would be off-topic.

Experimentation would be dangerous/unethical so the theory is all there is.

Assuming (based on common sense) that the metabolic differences work against and not in favour of swimming in crude oil as opposed to water, the 6..12 kg of negative buoyancy would not be compensated for by any increased metabolic capacity.

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    Re lifeguard brick test: I assume that the loss of one "swimming hand" to hold the brick would be more of an obstacle than the actual weight involved. If the brick were strapped to the chest it probably wouldn't be so bad. – Is Begot Jul 3 '14 at 19:45

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