Decompression needed for Chilean miners...?

[DandyDon]

We know that the news media does not know much about anything generally, and doesn't have time to check facts, but this story claims a risk: Ascent could bring bends, 'chokes' to miners – The Chart - CNN.com Blogs Excerpting...

Dr. Bailus Walker, an environmental and occupational medicine expert at Howard University Medical Center, says one concern is the effect the barometric pressure will have on their bodies as they're brought up. "You'll see muscular aches and pains in the joints called 'the bends' as a result of the decompression. You could see some respiratory difficulties called 'the chokes.' You'll see increased blood pressure, and some lung damage–but the adequate supply of oxygen should keep lung problems at a minimum."

The poor guys have a lot more to deal with: spinning capsule and lots more, but how much pressure change are they really looking at?

The San Jose Mine seems to be near the town of Copiapo 40 miles east of the coastal town of Caldera, with an elevation of 381 meters/1250 Feet, altho I cannot find the actual altitude of the mine. The miners are 2200 feet below surface, so I guess around 1,000 feet below sea level.

 

[knowone]

What pressure would the cavern have reached from the air being pumped down to them?

 

[DandyDon]

I don't think there would be much of an increase from the pumping as air escapes thru the ventilation shafts. A negligible increase if any.

 

[vladimir]

I don't think there would be much of an increase from the pumping as air escapes thru the ventilation shafts. A negligible increase if any.

I don't think so, Don. From a decompression perspective, the pressure in the mine is beneath the threshold of concern, if your back-of-the-envelope calculations are in the ballpark. But pumping air down will have a relatively large impact. Here's what a few minutes of googling turned up:

http://nopr.niscair.res.in/bitstream/123456789/2506/1/IJRSP 37(1) 64-67.pdf

In the Western Deep mine, refrigerated air is pumped into the depths, where the miners work through an insulated shaft in order to bring the temperature down to 28ºC. As a result, the pressure of air increases to twice that at the surface.

That paper predicts a pressure of 1.3 x surface at a depth of 3.5 kilometers.

 

[victor]

Since they have drilled a 23 inch hole from the surface we can assume that any excess air being pumped down will have escaped up the 23 inch wide hole they are going to use for the extraction.
So they are going to have a 1 hour ascent over 2000 ft. An aeroplane preasurises much faster than this so no risk.
Also when they have the escape pod it does not for a complete seal so air can escape around it.

 

[pjhansman]

Western Deep and most other large underground mines are supplied with air in quantities up to millions of cubic ft per minute, and the fans are capable of overcoming resistance pressures of up to 20 inches water gauge.

The volume of air required here is very low (no diesel equipment running) so resulting resistance/pressure is negligible. The miners in Chile will experience no more differential then you would if you went 2500 ft up in a plane.

 

[DandyDon]

I don't think so, Don. From a decompression perspective, the pressure in the mine is beneath the threshold of concern, if your back-of-the-envelope calculations are in the ballpark. But pumping air down will have a relatively large impact. Here's what a few minutes of googling turned up:

http://nopr.niscair.res.in/bitstream/123456789/2506/1/IJRSP 37(1) 64-67.pdf

That paper predicts a pressure of 1.3 x surface at a depth of 3.5 kilometers.

I did more than a few minutes of googling, but not in that area. Interesting paper. But even at a 30% increase approaching 1.3 ATA,* that's like spending a couple of months at 10 FSW. I don't see a decompression risk? These miners are 0.67 kilometer.

* Since the mine is not at sea level, it's at somewhat less that 1 ATA.

Since they have drilled a 23 inch hole from the surface we can assume that any excess air being pumped down will have escaped up the 23 inch wide hole they are going to use for the extraction.
So they are going to have a 1 hour ascent over 2000 ft. An aeroplane preasurises much faster than this so no risk.
Also when they have the escape pod it does not for a complete seal so air can escape around it.

And they have other shafts, don't they?

Western Deep and most other large underground mines are supplied with air in quantities up to millions of cubic ft per minute, and the fans are capable of overcoming resistance pressures of up to 20 inches water gauge.

The volume of air required here is very low (no diesel equipment running) so resulting resistance/pressure is negligible. The miners in Chile will experience no more differential then you would if you went 2500 ft up in a plane.

Ok, cool - so why are the deeper mines pumped so much harder? Does it take that much to offset the temperature increases, or in some?

I was thinking the same for these miners. Is the quoted expert just wrong? I met a physician in Lubbock once who owned the only hyperbaric facility with several chambers for treating burns & CO victims. He said he once treated a college boy for bends incurred from ascending the 800 elevator at Carlsbad Caverns. :silly: I put him on my list of quacks to avoid. I shudder to wonder what other ideas he may have sold to the local financing & medical market of people who don't know much about pressure changes. P. T. Barnum was certainly right, if he actually said that.

 

[Mr Carcharodon]

Water is a lot denser than air. Descending into a mine 1000 feet below sea level would increase ambient pressure by ~4%, which is about the same as diving in 1 foot of water. A direct ascent to the surface after a 1 foot dive should be possible no matter how long you stay. Decompressing may have been taken out of context in this case. Even if the mine is pressurized you would have to get up to close to 1 atm over ambient before there was a concern.

 

[CW2008]

Seems to me it would be no different than jumping in a small plane and ascending to the same height.

 

[pjhansman]

Ok, cool - so why are the deeper mines pumped so much harder? Does it take that much to offset the temperature increases, or in some?

The really deep mines are often the biggest as well. Volume of air is usually based on diesel equipment usage (about 100cfm/bhp), and on cooling requirements. The resistance from friction increases almost exponentially with volume so it doesn't take long for pressures to get much higher, particularly with the limited openings to deliver air (usually no bigger then 16 ft diameter) over long distances. Multiple fans greater than 1000hp are quite common. Refrigeration/cooling demands in the South African and Aussie mines are staggering.