Rank: Forum user 
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Hi,
We have used our multigas meter to take a reading of an underground sump. The alarm activiated for LEL % and the worse reading indicated 50% LEL.
I'm trying to work out what this reading is giving me. Is it saying the levels are 50% from the LEL level. Can anyone advise me please on how to interpret this?
Really appreciate this.
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Rank: Super forum user 
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http://www.canarysense.c..._lel_-_cg2-j-2_5-103.phpOk - my research is weak wikipedia :) - do not rely on my reply... However from a quick Google it would appear that this implies a conc of 2.5% in air which is 50% of the LEL of 5% Simples? or am I missing something :)
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Rank: Super forum user
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I expect teh_boy is correct.
However, it is rather important that you interpret this reading correctly so I would consult the instruction book for the meter and/or check with the manufacturer!
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Rank: Super forum user 
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The BOC MSDS for methane states that the flammability range is 5-15 vol% in air which confirms Weakipedia numbers. From that I would take the LEL to be 5% so, as stated above, you are at 2.5%. Confirm via the manual or tech support though
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Rank: Super forum user 
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Not all concentrations of flammable gas or vapour in air will burn or explode. The LOWER EXPLOSIVE LIMIT (LEL) is the lowest concentration of ‘fuel’ in air which will burn and for most flammable gases and vapours it is less than 5% by volume.
Safety procedures are generally concerned with detecting flammable gas before it reaches its lower explosive limit.
Flammable gas detection systems are designed to create alarms before gases/vapours reach an explosive concentration. Typically the first alarm level is set at 20% LEL
In my experience the LEL detector on these multigas meters is not that reliable.
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Rank: Super forum user 
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redken I agree with most of what you say. But part of your post may be misinterpreted ie "LEL is the lowest concentration of fuel in air that will burn is less than 5%"
Did you mean "explode".
Methane will burn below 5% in air if passed through a flame or igniting source, and between 5% - 15% will explode if ignited. Above 15% it burns if ignited.
Steve
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Rank: Super forum user
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If Confined Space Entry you should be looking at less than 10% LEL. It is typical to expect ignition at 50% LEL, hence most QRA would model extent to 50% LEL/LFL.
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Rank: Forum user
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When the concentration of methane reaches approximately 50,000 parts per million (ppm) in air, it forms a potentially explosive mixture. This concentration of 50,000 ppm is referred to as the lower
explosive limit (LE L). So your reading of 50% of LEL is 25,000 ppm
regards Dave
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Rank: Forum user
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4:1 Safety Factor on the LEL is typical, e.g. when you reach 25% of the relevant LEL alarms activate etc. Remember that such preseting of levels must be considered against the default sensor. Petroleum is normally based upon a sensor for Pentane - to use a 'petroleum Meter' for another gas or vapour such as Methane or Propane or Butane etc etc will mislead with potentially disastorous results. You need to incorporate your relevant correction factor.
A little knowledge can be a dangerous thing! RA's under DSEAR and confirm competence!
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Rank: Super forum user
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Safetyman
If you have 50% LEL in a sump then you have serious problem and will need some competent assistance in dealing with it.
As stated, LEL is 5% concentration in air or 50,000ppm. So at 50% LEL you have a concentration of 2.5%
Personally I would have the low level alarm on the detector set 1 or 1.25%
With the situation that you have ie 2.5% consider the following
- @ 2% or more withdraw staff and prevent entry
- @ 1.25% or more isolate power and prevent other ignition sources
- @ Identify the source of the CH4 and cause
- Establish mechanical ventilation. Force ventilate not extraction
Get some competent advice
Steve
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Rank: Forum user
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Ex Miner/or current miner by any chance Steve?
your last passsge takes me back to my days at St Helens College when i was studying Mining Techniques & Practice.
Al W
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Rank: Super forum user
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Well spotted.
Just something I picked up in a previous life.
Steve
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Rank: New forum user
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hi gents,
My last job was with drilling contrctor for Coal Bed Methane drilling. Personal Gas detectors we used had their low alarm set at 10% of Lower Explosive Limit (i.e. 5 % of Natural gas ,mainly methane ,in air) which means low alarm was set at 0.5% methane in air. A high alarm was set at 20 % of LEL (1 % methane in air).
Following high alarm emergency response is initiated on rig.
Abhijit.
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Rank: Super forum user 
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From memory of my British Gas days, 20% of the LEL was (is?) the level at which occupied premises are evacuated.
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Rank: Super forum user
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Personally I revert to my old chemical industry days and regard any indication above the zero point as indicative of action being required. Unless you are sure of the reasons for the excursion then you have no way of telling whether the LEL is about to be surpassed with potentially catastrophic consequences.
Bob
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Rank: Super forum user
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bob
I absolutely agree with you generally with that approach.
But in some environments eg mining, it maybe normal for there to be low concentrations.
But where the readings on the detector are abnormally high, show concern until you understand why, and be confident that things are under control before carrying on. Even when the abnormally raised reading is well below any alarm levels.
Steve
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