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Permalink Reply by weddew on April 21, 2010 at 15:40

Typically, a drilling rig has combustible gas detectors mounted in areas where the drilling mud is returned to the surface. The first place the gas will show up is in the returns (mud) from the drilling operation.

Combustible gas detectors are sensitive to natural gas and hydrocarbon liquid (oil & condensate) vapors. Since natural gas is primarily methane in composition the detectors are calibrated to measure methane in percent of lower explosive limit (% LEL). The Lower Explosive Limit is the minimum mix of methane and air that will support combustion, for methane that is 5% gas and 95% air (100% LEL = 5% NG in air). Typically, a warning alarm is set at anywher from 20 to 40 percent LEL and a shut down alarm no higher than 60% LEL.

The dual gas detectors you buy for home use measure methane (CH4) and Carbon Monoxide (CO). The methane alarm tells you when you have a gas leak and teh CO alarm tells you when you have a heater, stove, or hot water heater producing carbon monoxide which is deadly poison and has no odor. A correctly operation gas fired appliance will produce CO2 instead of CO.

Natural gas that has little or no hydrocarbon liquids associated with it is likely to have little or no odor. It usually does not get odorized until it is ready for commercial distribution.

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Permalink Reply by blueflame on April 21, 2010 at 16:36

Mr Tootin....Your saying that a concentration of methane (LEL) at levels of 1%-8%, in water being consumed by infants, is harmless? Seems like it would taste like moon-shine. That same concentration, mixed with air, would blow a person's house up. You better go back to Google and look again.

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Permalink Reply by weddew on April 21, 2010 at 17:16

Actually 1% to 8% LEL is well below the explosive limit. The gas concentration must reach 100% LEL for the mix to become combustible. 100% LEL is equal to 5% gas volume in air. 8% LEL is actually 0.4% gas volume. It is confusing when discussing percent LEL vs. percent by volume.

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Permalink Reply by ledlights on April 21, 2010 at 20:04

A quick aside from the natural gas issue and a few additions to what weddew already said - there are a lot of things worth knowing about CO

CO = carbon monoxide -> colorless, odorless product of combustion (gas, propane, oil, wood, coal, gasoline, etc., cigarettes) that is deadly because is binds to oxygen receptors in blood and causes oxygen starvation. CO detectors for homes are readily available - typically they just detect CO although dual gas detectors are more common now. Very good idea to install them if you have any combustion devices in your home or indoor space. Natural draft appliances are sometimes prone to backdraft if you have some big exhaust fans running in your home (clothes dryer, big range hood) The standards for allowable CO levels in exhaust gases for some combustion devices are not terribly stringent. Gas ovens for instance - my theory for some Thanksgiving drowsiness (besides being stuffed with food) is too much standing around the oven while the turkey is cooking. Blue flames from your gas range burners - good, Yellow flames - not so good. You should have a good air seal on the house door into your garage and if your furnace is in your garage and it has leaky return ducting it can suck in CO from you car into your home if you run your furnace and idle your car at the same time. The standard CO alarm level is 35 ppm, but folks with angina have experienced discomfort when exposed to levels as low as 10 ppm. Long term lower level exposure can cause serious health problems, while high level exposure can cause quick death as you folks know.

CO2 - carbon dioxide -> colorless, odorless non-toxic gas (unless at very, very high levels - very unlikely but can occur in caves) - product of human respiration among other things. Higher than normal concentrations indoors can be an indication of lack of adequate ventilation and can also indicate greater likelihood of unhealthy concentrations of other undesirable pollutants if there are sources of such stuff inside. Crowded rooms tend to cause sleepy folks and lots of yawning when CO2 concentrations exceed 1000 ppm.

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Permalink Reply by ledlights on April 22, 2010 at 8:42

I may have to take back my standard CO alarm level of 35 ppm statement. The 2 new CO detectors I installed in a house today go off at 70 ppm. And the instructions say get out of the house and call service/emergency crews immediately it those alarms go off.

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Permalink Reply by Mac Davis on April 22, 2010 at 11:39

Note that all these alarms, smoke, CO, or explosive gas do have a limited lifetime and need to be replaced. I've started buying smoke detectors with 10 year non-replaceable lithium batteries. You don't need to screw with the batteries every year and they sort of force you to replace the whole unit after ten years when you need to.

I had a CO detector go off with a false alarm in the middle of the night once. Scary situation to try to figure out while befuddled with sleep.

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Permalink Reply by ledlights on April 22, 2010 at 11:59

We put stickers on the ones we install saying when they expire. One brand we use automatically produces an error code at the 5 yr. expiration point. I believe typical lifespan of CO detectors is 5 to 10 yrs. depending on the kind of sensor being used.

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Permalink Reply by The_Baron on April 23, 2010 at 4:00

Main point if the CO detector goes off, open the nearest window! Get fre3sh air in quickly, then get out.

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Permalink Reply by ledlights on April 23, 2010 at 19:39

Absolutely. One other thing worth mentioning = many CO detectors measure levels lower than the alarm level. With some you can check the highest level recorded since the last reset - which may indicate a combustion device that needs tuning or repair and may also be indicative of a non-lethal level of exposure that if sustained could be dangerous. You should determine whether such levels are infrequent flukes or regular occurrences.

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Permalink Reply by Mac Davis on April 21, 2010 at 22:08

The manufacturer's info on my home CO/Gas detector indicates it should alarm at 25% of LEL. While that sounds good, it seems to me that you could easily have an explosive concentration around the bathtub, sink, or toilet without having 25% at a detector located nearby. Running the sink and flipping on a light switch in the bathroom might go boom before you set off the gas detector in the hallway.

It's probably a good idea to have the detector, but don't put too much faith on it.

In theory, methane is non-toxic. Maybe that really means it will blow you up before it poisons you or suffocates you. It would obviously be fatal if it displaces enough oxygen. I wonder if there are any toxic effects of methane dissolved in water.

Is it likely that there would be any other toxic gasses in a local drilling incident? Is there any significant H2S in the local rock strata? (Remember, not just HA depth, leaks can come from shallower formations.) Is there much CO2 in any of the local formations? Are any of the other underground gasses likely to be toxic other than suffocation or explosion hazards?

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Permalink Reply by sesport on April 24, 2010 at 2:42

IMO, this is going to put a big dent in consumer confidence as far as incorporating more ng appliances & mechanicals in the home as new home building ramps up again and as they make selections for remodeling or purchasing those new energy-efficient appliances that qualify for stimulus rebates. bummer ....

On the other hand, just about anything mechanical can be some kind of hazard no matter the energy source. Just have to be cognizant of the hazards (DO THE RESEARCH, READ THE OWNERS' MAUALS, FOLKS!) and take reasonable responsibility & precautions.

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