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Question - Gas detector for ironstone mine exploration


marcman

28DL Full Member
28DL Full Member
I'm looking to get a gas monitor for ironstone mine exploration.

My main question is, will a single gas monitor (o2) suffice?

I know the real danger with ironstone is low oxygen levels, but are there any other gas dangers in ironstone mines that would warrant a more expensive 4x monitor?

The monitor I'm looking at is a Scott Protégé ZM Single Gas Monitor. The main appeal is the price and the two year operating life, with no charging or calibration required. I realise that after 2 years it's useless, but in that time I would have spent way more on calibrations alone, on a 4x monitor, not to mention the more expensive outlay on the monitor itself.

Obviously I don't want to be a cheapskate with safety, hence I'm looking for opinions from those with better experience than myself.

Thanks in advance!
 

Oort

Fear is the little death
Regular User
I just bought a 4gas in the end, that way I know im covered. I was lucky and got one 2nd hand with charger and still in calibration for £100.

As Ojay says, CO2 can also be an issue in iron mines. Main reason why half the forest mines have restricted access to the lower levels.
 

cunningcorgi

28DL Regular User
Regular User
Really going to depend on what you want to get out of a gas monitor, i.e. chances are you might want to visit more than ironstone mines / other underground locations in the future.

Ironstone mines in general suffer from low oxygen levels as the iron in the rock oxidises to form iron oxide, leaving any non circulating air in the mine depleted in oxygen but as Oort and Ojay say, CO2 can also be an issue in them.

A single use O2 detector will tell you that O2 is becoming depleted but won't give an indication as to what is actually causing the depleting (a 4 Gas will indicate any rising CO2, Flams or H2S as well as lowering of O2).

If you are considering the outlay of a single use detector, I'd seriously consider going the whole hog and getting a 4 Gas in case anything does pop up, as your life is worth the extra few quid.
 

marcman

28DL Full Member
28DL Full Member
Thank you guys. If CO2 can also be an issue then yes, seems like I should go for a 4gas.

Does £45 sound like a fair price for calibration & test? Also how long does calibration generally last?
 

Ojay

Admin
Staff member
Admin
I’d also invest in an escape set. I have a drager which gives me 15 mins and is useful for sewer related stuff but I’ve also had to use it elsewhere. I also have full B.A but its bulky and not really practical unless you plan to venture into something that you’re desperate to see with very low levels of oxygen but that’s way excessive!

I’d deffo be purchasing or hiring an escape set though mate as some very low o2 levels occur in those places and can quickly be affected by atmospheric pressure too.
 

Ojay

Admin
Staff member
Admin
Thank you guys. If CO2 can also be an issue then yes, seems like I should go for a 4gas.

Does £45 sound like a fair price for calibration & test? Also how long does calibration generally last?
Yes that’s a reasonable price.

They need to be calibrated every 6 months, if you go over the sensor won’t be reliable especially the o2 will fluctuate and give inconsistent readings.

The biggest expenditure long term is that tied in with cost of sensor replacement, o2 is typically 2-3 years depending on what kit you purchase.

CH4/LeL 4/5 years max

H2S 3/4 years max

But that’s with some of the more expensive industry standard kit I have, cheaper meters will offer less in terms of sensor lifespan.

Like anything you get what you pay for and often the cheaper meters cost more in the long run as sensors are generally more expensive.
 

The Lone Ranger

Safety is paramount!
Staff member
Moderator
Carbon dioxide (CO2) is a colourless, odourless gas, normally present in the air we breath; "fresh air" has about 0.03% CO2 and about 21% oxygen (O2). (CO2 forms about 4% of the air we breath out - a low enough level for "mouth to mouth" resuscitation to work.) In caves and old mines the concentration is normally up to about 1% but can be higher due to rotting vegetation or wood, organic pollution carried in by water, poor ventilation or heavy "caver traffic" in small passages. Using a carbide lamp further depletes the oxygen level and adds to the CO2. CO2 is heavier than air and may form pockets of higher concentration in low areas, particularly where these are badly ventilated.

Anyone breathing a higher than normal concentration of CO2 will suffer gradually increasing ill effects, depending on the level of the gas, and may eventually become unconscious or even die if not evacuated. (The most famous casualty being Neil Moss, who became trapped at the bottom of a shaft in Peak Cavern.)
The Health and Safety Executive sets CO2. limits for the workplace: 0.5% for long term exposure; 2% for short term exposure; anything higher than this for any length of time is regarded as a risk to human health.
 

marcman

28DL Full Member
28DL Full Member
Yes that’s a reasonable price.

They need to be calibrated every 6 months, if you go over the sensor won’t be reliable especially the o2 will fluctuate and give inconsistent readings.

The biggest expenditure long term is that tied in with cost of sensor replacement, o2 is typically 2-3 years depending on what kit you purchase.

CH4/LeL 4/5 years max

H2S 3/4 years max

But that’s with some of the more expensive industry standard kit I have, cheaper meters will offer less in terms of sensor lifespan.

Like anything you get what you pay for and often the cheaper meters cost more in the long run as sensors are generally more expensive.
Been looking at pre-owned 'MSA Altair 4x' untis. No real way of telling how much life the 02 sensor might have left though. The calibration service includes testing so I guess that'll pick up on a dodgy sensor.
 

Oort

Fear is the little death
Regular User
Been looking at pre-owned 'MSA Altair 4x' untis. No real way of telling how much life the 02 sensor might have left though. The calibration service includes testing so I guess that'll pick up on a dodgy sensor.
If you go the 2nd hand route, make sure it comes with the charger and power supply. if it doesn't you'll be looking at another £50 odd on top.
 

Dan1701

28DL Full Member
28DL Full Member
The final thing I would add to all of this is that even with a warning device and an escape set, it is still wise to mark the route you came in with chalk or small glow-sticks (but pick them up as you go). The thing to remember with an ironstone mine is that the entire site was always operating on a tight budget, so there is likely to be only one way in and out. Cutting through rock costs time and money, so you only want one cut and maybe one ventilation and pumping shaft in the entire place.

That means that you have this network of tunnels isolated from the atmosphere with only one way for air to get in or out. If air pressure is high outside when you go in, or the wind is blowing onto the entrance (or is still), and whilst you're underground the pressure reduces for whatever reason then all that air down the mine won't be as highly compressed. That means that whereas before you had safe passages with enough oxygen in them, the depleted air from further down the mine (and the CO2 pockets) will expand and flow out, and what was safe before becomes unsafe quite quickly.

At this point a rapid exit is called for. Knowing that you came in THIS way past each of a series of glow-sticks might very well save your life.

I would also point out that of all the sensors, oxygen sensors are the trickiest to keep running and the ones which you should really not use if out of calibration. Low oxygen is also one of the most difficult atmospheric problem to detect of all the possibles, second only really to carbon monoxide (which you won't find in ironstone mines).
 

The Lone Ranger

Safety is paramount!
Staff member
Moderator
The final thing I would add to all of this is that even with a warning device and an escape set, it is still wise to mark the route you came in with chalk or small glow-sticks (but pick them up as you go). The thing to remember with an ironstone mine is that the entire site was always operating on a tight budget, so there is likely to be only one way in and out. Cutting through rock costs time and money, so you only want one cut and maybe one ventilation and pumping shaft in the entire place.
Personally I'd not put chalk marks on the walls, underground they don't tend to wash off and if everyone does it, it becomes a bit confusing as well as detracting from the mine.

Best way I've found is just take a pencil and paper and draw your own map as you go, you can then mark features on it even if it is just a discarded can, you then have it for the next visit and hopefully expand on sections you have missed. By all means use glow sticks, but take them back out with you afterwards.

Quick sketch done on my visit to the labyrinth of Facit Mine.

1357889_a289dca6eb9ab798bf0e93ff6412fbbb.jpg
 

crashed.out

28DL Full Member
28DL Full Member
At risk of reiterating what folk have already said in this thread, the first answer to your question is that an oxygen monitor alone does NOT give you sufficient protection in ironstone mines.

The chief dangers in most ironstone mines where chalk is also present are twofold: (a) low oxygen via any iron (II) compounds oxidising and scavenging elemental oxygen to do so to form acidic iron (III) compounds and (b) those soluble, acidic, iron (iii) compounds reacting with limestone to give off carbon dioxide. The UK's legislated short time exposure limit (15 minutes) to CO2 is 1.5% by volume. Assuming a nominal oxygen concentration of 21 % v/v, then you can reach the toxic level for CO2 and still maintain an oxygen level of 19.5% which is above the default alarm threshold on most monitors (19 % v/v).

CO2 sensing technology has improved greatly in the last 24 months. Old sensors used to top out below 1% v/v - I use the predecessor to this, which has an upper limit of 5% v/v: https://www.co2meter.com/collections/handheld/products/personal-co2-monitor Yes, it's not cheap, but what value do you put on not being poisoned??

For personal O2 monitors, Ribble Enviro do single gas meters from about £75 +VAT or so: https://www.ribble-enviro.co.uk/product/protoge-zm-single-gas-monitor/?gclid=EAIaIQobChMI_fCc16Ps4gIVCLDtCh0aNADQEAYYAyABEgKYAPD_BwE

You're unlikely to get any flammables such as methane unless you're very close to a coal seam too. H2S is a remote, but not impossible, hazard since rotting matter can emit it and there's been plenty of damp rubbish in the ironstone mines I know. If you want to go for a 4-gas sensor (N.B. to my knowledge there aren't any that combine CO2 measurement with a 4 gas - certainly the case 2 years ago), perhaps this: https://www.tomtop.com/p-e5806.html?currency=GBP&Warehouse=CN&aid=gplaukyly&mid=10000018477&utm_source=SEM&utm_medium=Google+Adwords&utm_campaign=TT_PLA_YLY&utm_content=2945&gclid=EAIaIQobChMIsZ6v5aTs4gIVzb3tCh2hHwYFEAYYBiABEgK7IPD_BwE

Don't forget the importance of regular calibration. These monitors can drift. And if you're trusting it with your life (which is essentially what you're doing), you want to be sure that it's accurate.

Also, in ironstone mines prone to CO2 don't forget the importance of measuring at different heights. It's possible for the CO2 to stratify - since it's twice as dense as air, it can exist in a layer on the ground. Diffusive and advective mixing is likely to be minimal due to the low and constant temperatures in these mines. That means, if you only measure CO2 concentration at head height and you kick up a low-lying CO2 blanket behind you, your exit is now highly compromised. Measure at ground level, measure at mid height and measure at breathing height. Bear in mind that the mine topology and geology will change as you go through it - so will the gas profiles. Get used to, and get in the habit of, constant dynamic risk assessment. Make sure that your contingency plan isn't invented on the hoof once shit has hit the fan...

This will be on top of the usual hazards in abandoned mines such as roof collapse, getting lost, vertical structures above you or below you and the possibility of rotting, false, floors. Do some research beforehand and know your enemy!

Hope this helps and keep safe.
 

cunningcorgi

28DL Regular User
Regular User
All very sensible stuff there @crashed.out but @Ojay and @pirate have touched on probably the single most important element to consider when entering a mine.

Athmospheric pressure.

There was a reason that all working coal mines had to have a barometer at banktop. And it wasn't for decoration. The air in mines changes hourly / daily and it is all down to what is happening outside the mine more than what is happening inside.

'When it rains, stay out of drains' as the saying goes. We'll have to get one for old mines. 'When the pressure is down, don't be a clown' for example !!
 
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