Me and my mate where down in Minera Lead Mines the other day and my 4 gas kept going off because of high O2. The funny thing is that it was very localised in a few places. Any body got any ideas what would be causing the high O2?

Any idea what the air pressure was that day?

Couple of threads you might find relevant on air pressure and effect on air quality in mines:

http://www.aditnow.co.uk/community/viewtopic.aspx?t=4183  and http://www.aditnow.co.uk/community/viewtopic.aspx?t=4390 

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High O2?
Out of calibration or a diffy O2 sensor are the most likely reasons.

High O2?
Out of calibration or a diffy O2 sensor are the most likely reasons.

Yep, high O2. There is a major problem with your statement in the it was calibrated on a few months ago and that I was getting the same reading in the same places in the mine. It wasn't just going off randomly.

Any idea what the air pressure was that day?

Couple of threads you might find relevant on air pressure and effect on air quality in mines:

http://www.aditnow.co.uk/community/viewtopic.aspx?t=4183  and http://www.aditnow.co.uk/community/viewtopic.aspx?t=4390 

Cheers.

The air pressure was around 1005 mb.

What was it reading on the surface?

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What was it reading on the surface?

20.9% Like it should. I'll have a look at the data log later.

What was it reading on the surface?

20.9% Like it should. I'll have a look at the data log later.

What was the max O2 reading underground?

What was it reading on the surface?

20.9% Like it should. I'll have a look at the data log later.

What was the max O2 reading underground?

23.1% with the next highest being 22.5%. :confused:

Generally high O2 readings occur when the air pressure has either gone up, or you calibrated in poor air and have gone into good.

Now, I've given up with gas monitors, as I think they are an expensive load of fuss.

There is another possibility and since I have no idea what the "magic gubbins" in a Gas Detector is, I'm not 100% sure what the particular culprit could be. If you had a gas lamp/lighter, you wouldn't be bothered by this arcane trivia...... The idea is that since the O2 sensor works by an electrochemical reaction, that something airborne is causing the reaction to proceed quicker. It could be something solvating the reaction product away, or some sort of weird "half cell" reaction where some gunge is being oxidised/reduced/etc at the sensor. I have no idea what probably-fine-droplet-borne shizzle could do this, but it's most certainly possible, given the complex chemical pathways still proceeding in long dead mines.

Using yourself, a davy lamp and a lighter is a lot cheaper and in my mind, makes a lot more sense.

We've been into mines and the detector has gone so haywire, it's almost been a waste of time having the bloody thing.

A strange anomaly. I must have used various gas detectors many times in all sorts of conditions, the only thing they did not like was sucking up water when using the sample tube or testing with acetylene or propane straight from the bottle!

It is very strange. I was hoping for some sort of informed and insightful answer but the more I explore mines and other underground stuff the more I realise that it's an alien environment for us simple apes!

Not sure if this is relevant, seems to be about non-portable sensors.

"The operating principle of this detector is based on the fact that oxygen atoms are strongly attracted to a magnetic field, ie they are paramagnetic. Measuring the differential interaction between the magnetic field and the target gas and a reference gas generates a response proportional to the oxygen concentration.
This sensor measures oxygen in the range 0-100%. It has a fast response. If the instrument is calibrated in one direction (eg north-south) and is used in another direction (eg south-north or east-west) there will be some offset. Paramagnetic sensors are not often used in portable instruments because of this orientation dependency and tend to be less rugged than electrochemical sensors."

I would have thought measuring increments of O2 via electromagnetism was some exceedingly sensitive gubbins in a very controlled environment.....or some very very very expensive stuff!

I'll stick to my Davy lamp.

Thanks for the info, it made me remember the difference between paramagnetic and magnetic, which I assume is a distinction (without counting electrons at this time of night) in the separation of Tin and Tungsten.....magnetically....

It was the only bit of info when I Googled 'O2 detector error' and a few other phrases.

as a diver we calibrate our 2 detectors each time we use them, Orientation relative to north is irrelevant to magnetic north, it's an electrolytic process. the hig O2 is odd, I'd check calibration when you come out too. this information is else where on the forum too.

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We had a moment the other day, one of our party complained of being "tired" while at the far end of Stanhopeburn Widley water level ,never noticed it myself until I found I could not light a cigarette, the lighter was sparking but would not ignite .

This is a good reckoning of lighters/candles and stuff:-


http://wasg.iinet.net.au/Co2paper.html 


If you had been exerting yourself, it would have been dizziness/tunnel vision territory.