Draught testing challenge

Pitlamp

Pitlamp

Well-known member
There are two caves a couple of kilometres apart. One draughts inwards in hot weather and the other (at lower level) draughts out. It would be useful to know if there is an air flow connection between the two caves.

Can anyone think of a way of labelling the inflowing air in such a way that it could be detected at the outwards draughting cave (in the manner of water tracing)?
 
tomferry

tomferry

Well-known member
Interesting post , I look forward to hearing some other people?s answers .
my Only idea would be to go in as far as possible and spray some extremely strong smelling stuff but this could obviously lead to breathing difficulties inside for the people in their ? Unless it was not harmful in anyway mmmm this is going to take some thinking  :-\

Atmospheric pressure will certainly play a vital role in this test on a crystal clear day if you sprayed the chemical for example I imagine it would be sucked deep inside the cave system , on a extremely cloudy day it would more kick it back out in your face  .

You will need to no the hole day is not going to change ie any clouds at all as a change in the pressure will turn the ventilation around and push the for example spray back out the same way ! Maybe a barometer might also help in this .
 
PeteHall

PeteHall

Moderator
First thoughts are that if there is a large volume of air in between (which would be expected with a strong draught) anything you put in will be diluted within the cave and you're very unlikely to see anything at the outflow, whether or not they are connected.

Imagine using a hosepipe with red dye at one end of a swimming pool and an outfall at the other end. while switching on the hose would cause water to come out of the outfall almost immediately, you would need to put in a huge amount of dye over a long period before starting to see anything come out the other side.
 
AR

AR

Well-known member
Joss sticks - a bundle of something with a good strong scent should hopefully be detectable at the lower end if there is a connection? Smoke pellets would be another alternative for something visual.
 
mrodoc

mrodoc

Well-known member
There are some extremely strong substances about if you do some research.  Also very small particles eg pollen might go through and could be captured
 
Rob

Rob

Well-known member
We've used joss sticks very successfully, but i highly doubt they'll work over that distance. May be worth a go with lots and lots of them, but make sure the sniffer or their clothes don't come in contact with them beforehand at all.

At the possible detriment to the cave, you could place a datalogging carbon monoxide detector at the lower cave and have a really bad bonfire in the other. This logger is less than ?100 and may work?
https://uk.farnell.com/lascar/el-usb-co/data-logger-usb-carbon-monoxide/dp/1006159
Would want to log for a long time before and after to prove it's an unusual variance. No idea if the ppm would be in the detectable range though...
 
A_Northerner

A_Northerner

Active member
Rob said:
At the possible detriment to the cave, you could place a datalogging carbon monoxide detector at the lower cave and have a really bad bonfire in the other.
Click to expand...

"The good news is there's a connection, the bad news is we now need breathing apparatus to get through it"
 
aardgoose

aardgoose

Member
Apparently SF6 is banned for use as a tracer gas in the EU.  The electrical industry is pretty strict on leakage from all the HV switchgear it is used in as an insulator.

You could get the stuff they use in natural gas, and that way you get a free monitoring service as everyone nearby reports a leak.
 
Bob Mehew

Bob Mehew

Well-known member
Odorizers are used to add a smell to natural gas so as to alert one to a leak, see https://en.wikipedia.org/wiki/Odorizer .  The problem will be the dilution with, as has been pointed out coping with the high concentration and potential toxicity at the release point and sensing it at the other end.  There could also be a major potential problem in the substance being taken out of air whilst traversing through the system such as due to solubility in water.  Ari's comment about SF6 is good as it is a fairly passive chemical compound but one would need a fairly sensitive mass spectrometer to analyse samples.  It might just make a final year project for an undergraduate chemist who has access to a lab with a spectrometer in it.  Some analysis systems concentrate up the molecule of interest but I have no knowledge of examples other than carbon for C14 / C13 / C12 analysis.

I guess the real challenge is a 'do not detect' result does not equate solely to 'no connection'. So one would probably have to start with a known system to demonstrate the idea works.  (And take care with atmospheric pressure changes.)

PS in place of SF6 how about Helium or Argon?
 
Leclused

Leclused

Active member
All you need to know about airflows can be found in some very interesting books from B Lismonde.

At the bottom of the following page you can find the links to these books in PDF (in French)

http://mdemierre.speleologie.ch/?p=1077

Some measuring tools can be found on www.testo.com

Measuring nanoparts : https://www.testo.com/en-UK/products/products_nanoparticle
 
2xw

2xw

Active member
Is the volume coming out the same as the volume coming in, controlled for passage size
 
pwhole

pwhole

Well-known member
I was trying to resist suggesting smoking-related solutions! Funnily enough I just offloaded a box of old cigars to a mate as I haven't smoked one in a decade, but he's not a caver sadly :)
 
C

crickleymal

New member
aricooperdavis said:
SF6 is used for mine ventilation system testing (it can be detected at 1 part per billion) - but I think it requires taking air samples out for analysis rather than allowing in-situ detection.
Click to expand...
SF6 is used for arc suppression in high frequency waveguides in (for instance) radiotherapy machines. We used to purge the waveguides every time we had to change a magnetron and when I started back in 1991 we used to empty it outdoors. Nowadays it has to be securely contained and taken to a disposal facility.
It's also heavier than air and will settle in any hollows and is an asphyxiant.
 
Bob Mehew

Bob Mehew

Well-known member
crickleymal said:
It's also heavier than air and will settle in any hollows...
Click to expand...
sorry but that is incorrect.  Badino at https://caves.org/pub/journal/PDF/v71/cave-71-01-100.pdf provides a readable (not much maths) explanation of why not.  Alternatively if SF6 (molecular weight 146) did settle out, then we would all be dead because xenon (molecular weight 131) in the air would also settle out.  The key mitigating factors are drafts and thermal currents which mix the air sufficiently to stop such stratification. 

The simple explanation for CO2 apparently ponding is because it is being evolved in the zone and is not be diffused away fast enough.  The same would be true around the release point of any gas.  But release volume dependent, beyond a certain distance only dilution will occur.
 
Pitlamp

Pitlamp

Well-known member
Some great discussion here already; thanks everybody.

I'd assumed that some sort of remote detecting would be necessary, sensitive enough to pick up low concentrations well below olfactory detection levels.

The pollen suggestion is an interesting one; it makes me think of spores too.

It was suggested above that it'd be a good project for a chemistry student; I wonder if anyone would be interested. (The site is in the Dales, by the way.)
 
Mark

Mark

Well-known member
I remember when we worked at Sallet Hole you could often smell if someone was peeling an orange in the mine.

I also recall that eucalyptus oil was to be introduced into the ventilation system as a warning to vacate the mine in an emergency, depends how strong the draught is I suppose
 
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