Mercapten is reported to have an odour at a concentration of down to 1 ppb (part per billon or 1 in 1,000,000,000) see https://en.wikipedia.org/wiki/Methanethiol. If I have it correct that is equivalent to 1 gram in 1,000,000 metre cubed or roughly the volume of 23 Gapping Gill Main Chambers (Descent 229 p26). So it has potential. But given it is also toxic above 10 ppm (parts per million), safely releasing it presents a challenge. (Oh and it is also explosive up in the % range.) One potential problem is that it is soluble in water, so could be 'washed' out.
The challenge with lycopodium spore is that each spore is heavier than air and can, when making contact with a surface (especially one which is damp or wet) stick to that surface. So the spore will be 'filtered' out as the current of air wafts it way through the passage. Maybe OK for a few tens of metres but hundreds of metres doubtful. If one has access to a mass spectrometer, then one could use an inert gas. Argon won't work since it naturally present at just under 1% in air.
How about using some poly sheet and a large fan at one end or the other to try to engineer a draught reversal? Only a small change in pressure may be needed and no fumes to worry about other than from your generator for the fan.
Another concern about the lycopodium spore approach is how do you capture the remaining spore at the other end? Using dyed spore might also foul up the system from being able to use dyed spore for water tracing.
Lycopodium spores evolved to get everywhere. they will get everywhere!
Thanks folks, some really useful information above.I feel like I'm slightly getting out of my depth here; just wondering if anyone who knows what they're doing might be interested in taking this little project on, next spring / summer? Apart from the interesting riddle we're trying to solve, if a method could be devised which is successful, this would then be available for others to use in similar circumstances in the future.If anyone's interested, maybe PM me? (It's only a few miles from Ingleton, by the way.)
Any suggestions for a simple but long system which one could place detectors in without the need for gear? Imposing a signal needs some thought.
I don't think I ever gave details in this topic of the reason I originally asked the question. Austwick Beck Head has been extended this year, mainly by diving. Sump 1 is short and in dry weather there is a thin airspace. There has been an inward draught here right through the warmer months of 2021. But there should have been an outward draught in hot weather, if ABH is the lowest entrance of the system it drains. (Sump 2 beyond is never unroofed and the draught goes into a choked bedding above water between the sumps, which is yet to be investigated properly. Sump 1 is not safely passable without diving gear by the way, as the route through involves complete submersion, whether or not airspace exists, via a couple of awkward restrictions.)There must be another entrance which is low enough to generate a convectional draught. Contenders include Blind Beck Cave (22 m lower) and Beck Head Stream Cave (32 m lower). BBC has a feint outward draught in warm weather; BHSC has a strong outward draught. Could either of these two air currents originate from ABH?Being able to trace such draughts, in the manner of tracing water, would be a very useful technique to develop for cavers generally. Maybe a BCRA field day, bringing folk together who are interested, might be of value?
Right. I think https://pythontic.com/visualization/signals/fouriertransform_fft shows the basic process (ignore the coding). Let's assume we have 4 sensors, A outside entrance 1, B inside entrance 1, C outside entrance 2 and D inside entrance 2. So the challenge is taking data from the 4 sensors, applying the Fourier transform to each data set (and presumably sub sets over specific time periods) and see if one gets similar frequency components. Hopefully one might see the same frequency components from sensor B & D but not from A & C. There is a possibility that the sub sets might show up a time slip between sensors B & D and also A & C. I guess the first thing is to try it out on a simple top & bottom entrance and hope wind conditions will provide the variable signal. Any suggestions for a simple but long system which one could place detectors in without the need for gear? Imposing a signal needs some thought.
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