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Porter ranch methane leak 8

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moon161

moon161

Mechanical
Dec 15, 2007
1,184
The Aliso Canyon gas leak:
is a leak in a gas well connected to the sort of underground natural gas storage facility, which now is supposed to represent 1/4 of california's global warming footprint, and is sickening thousands in the nearby neighborhoods, not to mention the freaky infrared pictures of the methane plume

Apparently the self-regulated utility removed a shutoff valve decades ago
I think environmentally, this will make the VW scam look like peanuts.
 
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I can see the wellheads, just a few miles away, from my office window as I type this. My commute takes me closer to it, and I have never smelled the mercaptan once.

My colleagues who live very close aren't worried. One colleague who lives very close thinks it's all hysteria, and hasn't even thought about evacuating even though he has an under-one-year-old baby. He says he's just caught a whiff of the mercaptan a couple of times.

No one has been "forced to leave their homes" in the sense of mandatory evacuation. Yes, many people have thought that it would be prudent to evacuate, and loosely speaking, have felt "forced", but my understanding is that the majority of people in even the closest neighborhoods have stayed.

When I first moved to LA, I was literally across the streets from the La Brea Tar Pits ("the the tar tar pits", my kids liked to joke when they studied Spanish). You could watch the methane bubbling up non-stop there. While I lived there, there was an explosion in a nearby store from methane buildup. Now most (all?) of the buildings around there have prominent methane detectors.
 
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cswilson,
Thanks for bringing up "the the tar tar pits" (I had a teacher in 5th grade in Lakewood point it out to us, but I hadn't thought about it in years). I bet the businesses around the pit do have considerably more methane in their buildings than the houses around the "disaster".

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
 
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zdas,

There's an old joke in LA that "they ruined a perfectly good oil and gas field by building a city on top of it". There are many, many battles around the LA area about emissions from oil and gas drilling for neighbors that don't make national news.

After that methane explosion in the late 1980s, the local congressman, Henry Waxman, pushed through an amendment in Congress that banned the use of federal funds for subway construction in that area, on "safety" grounds. This derailed the planned "Subway to the Sea", and a lot of people thought that the real reason for the ban was that the subway would allow the "wrong kind of people" to get easily from downtown to the affluent communities nearer the ocean. Beverly Hills was particularly opposed.

Now the area is completely gridlocked at rush hours, so there is the political will to extend the subway through this area. I've talked to people in this field, and they tell me that any underground work anywhere in LA must always be vigilant for methane buildups, with constant monitoring and extensive ventilation. They don't see that the Tar Pits area is significantly worse than others. So now my old apartment building is slated to be torn down for a station by the Tar Pits.
 
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IRStuff,

Thanks for the link. Very interesting! But there's a huge difference between the levels to be able to detect a substance like mercaptan and the levels that could cause harm. The sources I've seen give a 1.6 ppb typical detection threshold, which is very likely far, far below the levels that could cause any harm. The only case of harm I've been able to find was a worker who was dealing with tanks of the "pure" stuff.

I agree with those who think that without the mercaptan, there would probably be no story, even though it's a tiny, tiny component of the leak. It is ironic that the whole point of adding the mercaptan is to annoy the hell out of people, but that's really for fire safety purposes.
 
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But, mercaptan is not a harmless material: While there may be some confirmation bias at work, the supposed symptoms of mercaptan exposure are consistent with those reported by the residents. Note also, this link mentions olfactory fatigue, and that children, with a higher lung area to body mass and shorter stature, can receive higher doses than adults. Mercaptan is heavier than air, so children who are closer to the ground would be more susceptible.

TTFN
I can do absolutely anything. I'm an expert!
homework forum: //faq731-376 forum1529
 
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I know when my dog pegs a skunk close-in the smell can make me want to hurl rather badly. So poison or not a smell could screw up a person's life/function.

Keith Cress
kcress -
 
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Most natural gas has no more than 0.5 grain (8 ppm) of mercaptan. Some analogies that may help you visualize the scale involved with ppm. One ppm is like:

• one inch in 16 miles,
• one second in 11.5 days,
• one minute in two years, or
• one car in bumper-to-bumper traffic from Cleveland to San Francisco.

The major fate of atmospheric methyl mercaptan is photooxidation. The estimated atmospheric lifetime is only 1.2 hours.

The daily California smog has more effect than the mercaptan.
 
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That would be true if the natural gas was intermittent or diluted. However, there were measurements of natural gas on the order of 0.4%, which is pretty significant.

TTFN
I can do absolutely anything. I'm an expert!
homework forum: //faq731-376 forum1529
 
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There are maps galore, but this one does show much higher level at least once:


Porter Ranch is in an area that can often get high winds, so open areas are likely to get swept clear of gas, otherwise, people would be dropping like flies. Nevertheless, enclosed or walled areas might not get swept, and might accumulate mercaptan in higher concentrations. Even the guy from AQMD on NPR this morning seemed somewhat unclear about the fact that methane is odorless, and should have be referring to the mercaptan. But mercaptan is simply mixed with the methane, so there's no mechanism for keeping them together. You could blow away all the methane yet still retain the mercaptan, since it's heavier than the methane.


"That is a stretch."
Why is that a stretch? That was directly from the CDC.

[URL unfurl="true" said:
http://www.atsdr.cdc.gov/MHMI/mmg139.pdf[/URL]]Children exposed to the same levels of methyl mercaptan as adults may receive a larger dose because they have a greater lung surface area:body weight ratios and higher minute volume:weight ratios. In addition, they may be exposed to higher levels than adults in the same location [COLOR=3465A4][highlight #EF2929]because of their short stature and the higher levels of methyl mercaptan found nearer to the ground[/highlight][/color].
Click to expand...

TTFN
I can do absolutely anything. I'm an expert!
homework forum: //faq731-376 forum1529
 
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You are comparing apples and oranges. The CDC sheet is referring to chemical exposure where the person is in contact with or near the source of a concentrated chemical spill. The Porter Ranch scenario consists of a few ppm of chemical (mercaptan) with the person being over a half mile away. That is the stretch.
 
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"The Porter Ranch scenario consists of a few ppm of chemical with the person being over a half mile away. "

How is that the case, given that both your link and mine show measurements of higher than background concentrations in the middle of neighborhoods, and these are only spot checks? Even your citation of 230 ppm, which was measured on Nov 11, was measured in the vicinity of the cul-de-sac on Turtle Springs Ct, where there were at least 9 houses within 100 ft of that measurement.

TTFN
I can do absolutely anything. I'm an expert!
homework forum: //faq731-376 forum1529
 
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The reply is to your reference of the Medical Management Guidelines for Methyl mercaptan. I added the chemical name to clear up your misunderstanding.
 
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IRstuff, methane is much less dense than air (16/32). There is only about 6ppm of mercaptan added to the methane. Once mixed, gasses of differing density never separate because molecular diffusion keeps them mixed. So your statements about the possibility of mercaptan accumulating in low spots is really off-base. The 230 ppm measurement you mention is methane concentration, not mercaptan.
 
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Compositepro,
I don't think your units are right. The injected number is in the ppb range, not ppm. My experience agrees with yours. With widely differing gas densities it is a real chore to get them to break back up, and you get no measurable gravity separation of gases.

bimr,
Thanks for the time series data on concentrations, I've seen some of it, but not that much.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
 
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For my own education: The last two posts talk about gases of differing densities being hard to separate. Are you saying that all gases are hard to separate, that gases of different densities are especially hard to separate or just that a density difference does less to make it easy than you might at first think?

Sorry for the digression.

A.
 
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Methane gas has a specific gravity around 0.6. Mercaptan specific gravity is around 1.4. About as big a difference as you are likely to find in real life. We put a bit of mercaptan in natural gas and rely on it staying well mixed for years in storage fields. And it does.

I've seen samples taken at the top, middle, and bottom of very tall towers that were shut in and the mix of gases was the same in each location as the other locations.

Gases do not gravity separate. We get the idea that they will because if the combined mix of gases (say, you've mixed hydrogen and helium with propane until the blended specific gravity is greater than 1.0) then the mix will settle and you can get hydrogen and helium in a sample taken at ground level. Over time the mixture will blend with air until our three added gases can no longer be found, but as long as there is a substantial portion of the propane the mix will stay close to the ground.


David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
 
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