Pollution from Hemel hempstead
December 14, 2005 3:01 AM   Subscribe

Is the pollution released by the Hemel Hempstead oil fire greater or less than the pollution that would have been released if that fuel had been refined and used to power cars etc?
posted by Pericles to Science & Nature (26 answers total)
I would presume presume greater, given the lack of emission control devices, the less efficient burn, and the combustion of all the non-fuel material (buildings etc).
posted by pompomtom at 3:43 AM on December 14, 2005

Yeah, especially since all the oil stored there was fuel and was intended for burning. The only thing that might tip the scales is if a significant portion of the oil stored wasn't burnt and won't be reclaimed but instead gets gotten rid of in some manner that doesn't fall under your definition of "pollution".
posted by fvw at 3:57 AM on December 14, 2005

That said, I'd be pretty sure there's less pollution at ground level in this case. Having all that petroleum burned up by cars around London would cause bigger health problems than hundreds of tons of soot being deposited over the entire south east of the country, no?
posted by wackybrit at 4:48 AM on December 14, 2005

The soot is certainly more toxic than the gas that would be emitted by efficient combustion, which would be mostly CO2. Black cloud = bad in this case. One MP asked about the polycyclic aromatic hydrocarbons. Basically, if it isn't burning to CO2 but it's burning to something particulate, it's going to be nastier than CO2.

You might also be tempted to consider as pollution all the foam they used to fight the fire.

I think the unburned fuel from the fire will probably have to be incinerated since the tanks would be full of ash. The tanks that didn't burn might either be okay, or need to be re-refined.
posted by sagwalla at 5:01 AM on December 14, 2005

Almost certainly greater. Single uncontrolled although relatively short-lived environmental incidents can pollute more than an entire year of normal activity.
posted by sciurus at 6:46 AM on December 14, 2005

The same. Conservation of matter. The pollution may just be in a different form, but the amount is the same.
posted by Pollomacho at 7:26 AM on December 14, 2005

You might also be tempted to consider as pollution all the foam they used to fight the fire.

In this case let's take into account the pollution caused by the wearing of tires, burning of motor oil, the manufacture of sheet metal for the automobiles, the forming of that metal into parts, the feed lot that housed the cows that were processed into rich corinthian leather for the seats, etc...
posted by Pollomacho at 8:11 AM on December 14, 2005

Well, all that oil will be replaced, and the replacement oil will also get burned. So it's not like the fire is instead of burning in cars or furnaces; it's in addition to those uses.
posted by Kirth Gerson at 8:21 AM on December 14, 2005

Greater unquestionably.

Engineers put a lot of effort into making sure that engines, whether static generators or vehicular burn cleanly. Open air fires typically run anoxic, with too little oxygen for complete combustion, unless in near gale-force winds. This results in many fairly nasty combustion products.

The major visible output from poor combustion is soot, often called particulate matter emissions. Soot is produced in a wide variety of sizes, with the smallest being by far the most dangerous. Particulate matter less than 10 micrometers in size, commonly called PM10, is considered to be a very high respiratory hazard. When a soot clump gets into the lung, the body seals off the alveoli that contains the particle permanently reducing lung capacity. Particulate matter exposure can also induce asthma. Patriculates also carry all of the compounds I'll discuss below. Soot inhalation, as well as being bad all on its own, is also a major exposure mechanism for combustion chemicals.

Also produced in oil fires are any number of incomplete combustion products. The most significant of these from an environmental and human health standpoint are the aromatic compounds. These include polycyclic aromatic hydrocarbons (PAHs), biphenyls, and dioxins. It's important to note that since there was no plastics involved, the chlorinated analogue of these products will not be produced, so the dangers from the biphenyl and the dioxin components are considerably reduced.

PAHs are dangers in the non-chlorinated forms however. PAHs, for those who remember their high-school chemistry, are multi-ring aromatic compounds, 2 to 5 rings of benzene glued together. There are larger ones, but those are the ones that are most important in terms of toxicity. Now, if you read most of the regulations out there (and I'm not familiar with the UK ones, but this is certainly true of my side of the Atlantic), almost all defined exposure levels are for the bare ring non-derivatized forms of the PAHs. Petroleum is unusual in that the majority of the PAHs are in alkylated forms, with 1, 2 and 3 alkyl-derivatives being the most common. This means that the PAH multiple ring "backbone" has 1, 2 or 3 extra lumps of methyl, ethyl and propyl groups glued on the outside edge of the molecules. When burned, there's a strong tendency to form more highly alkylated forms: the 0- (bare), 1- and 2-akyl forms largely disappear in the flame emissions with 3- and 4-alkyl derivatives predominating.

Why is this important? Two reasons: First, most commercial labs will only test for the 0-alkylated (bare) PAHs because that's what the regulations are written for. Secondly, while data is very sparse, it appears that the alkylated forms are considerably more toxic than the non-aklylated forms. The most common acute toxic effect of the 0-alkylation PAH exposure is narcosis, but that takes a considerable amount of material. By contrast, the highly-alkylated forms are implicated in CYP1A induction and teratogenic effects (in animal models at least). The CYP1A pathway is probably the most potentially damaging one. There's lots of things that can go wrong because of P450 activation, cancers, liver failure being the ones that immediately pop to mind.

Sorry for the long and perhaps overly technical answer, but this is pretty much the current knowledge of what petroleum burn fate and effects are. If you have any specific questions, ask and I'll try to answer.
posted by bonehead at 8:58 AM on December 14, 2005

Conservation of matter. The pollution may just be in a different form, but the amount is the same.

Here's a thought experiment: would you prefer to (a) hold a one pound chunk of (solid) lead in your hand, or (b) have that lead in the form of tiny particles that can be ingested (as was the case when leaded gasoline was legal in the U.S.)?

Form does matter. Comparing a volume of carbon monoxide and carbon dioxide, there may be equal amounts of carbon, but the first will kill you even in low concentrations while the second is only dangerous if it essentially crowds out all the available oxygen.
posted by WestCoaster at 10:31 AM on December 14, 2005

You're understating the lethality of CO2, but yeah, CO is worse.
posted by Kirth Gerson at 11:24 AM on December 14, 2005

do these arguments include transport costs and other energy coniderations?
posted by wumpus at 11:24 AM on December 14, 2005

The CO2 vs. CO debate is moot. The CO from combustion is only an issue in confined spaces, as I understand it. Outside, as this fire was, CO isn't a major toxicological concern. The soot and the VOCs are because these are what people and the organisms we share our environment with are exposed to. The CO disperses to harmless levels very quickly.

And it hasn't yet been considered, but I'll mention here for completeness: the residue left over from pool burning (which can be up to 50% by weight) is generally less toxic than the starting oil. The toxic components of oil, primarily the aromatics, the monoaromatic BTEX and the multi-ring PAHs, are volatile and tend to get drawn into the flame.

Finally, I would not expect fire-fighting foam to produce much toxic residue. They're designed to be as innocuous as possible and to inhibit burning.
posted by bonehead at 11:47 AM on December 14, 2005

Wikipedia: Carbon Dioxide
OSHA limits carbon dioxide concentration in the workplace to 0.5% for prolonged periods, or to 3% for brief exposures (up to ten minutes). OSHA considers concentrations exceeding 4% as "immediately dangerous to life and health." People who breathe 5% carbon dioxide for more than half an hour show signs of acute hypercapnia, while breathing 7%–10% carbon dioxide can produce unconsciousness in only a few minutes. Carbon dioxide, either as a gas or as dry ice, should be handled only in well-ventilated areas.
posted by ryanrs at 5:48 PM on December 14, 2005

You guys are making moutains out of molehills here.

There is very good field data on petroleum fires and considerable practical experience on the ground. Niether carbon dioxide nor carbon monoxide is a problem for responders, workers or people downwind in open-pool fires like the Hampsted event. These fires are very dangeous for other reasons---look up BLEVE in Wikipedia---but they do not produce enough ground level CO2 to be an asphixiant, nor enough CO to cause hypoxia.

The highest CO2 levels we've seen on a pan- or on-water burn is 600 ppm (thats 0.06%) on monitors right at the base of the fire. It's almost impossible to detect CO above background.
posted by bonehead at 7:47 PM on December 14, 2005

Yes, the CO/CO2 discussion is not really relevant to the fire in question, but I felt it necessary to respond to
the second [CO2] is only dangerous if it essentially crowds out all the available oxygen.
You can get killed by fairly low concentrations of CO2, as ryanrs's quote says. Even those concentrations are unlikely except in a confined space.
posted by Kirth Gerson at 8:10 PM on December 14, 2005

Nobody's spoken to nitrogen compounds yet?

Nitrogen burns at higher temperatures -- that's why external combustion engines pollute less than internal combustion engines, they're burning the fuel at one atmosphere pressure, rather than in compression -- so at a lower temperature.

No idea what the tradeoff is, but they count -- they're what make the photochemical part of smog, the stuff you don't see in the air after a long weekend or after a storm blows through, but you start to see getting thicker at the end of the first clear sunny day and building up while there's a high pressure/stable air mass in place.
posted by hank at 6:25 PM on December 15, 2005

You can get killed by fairly low concentrations of CO2

Really? I'm going to have to see some references on that. Wikipediea is in error, if that's what it says. Every guide I've got lists gaseous carbon dioxide's primary lethal effect as an asphyxiant. It kills by oxygen displacement. There are blood and CNS effects, but acute lethality with CO2 is almost always attributable to asphixiation. See here under the notes section for a typical warning on exposure.
posted by bonehead at 7:57 AM on December 16, 2005

Hank: you can make your own assessment. Go here, put in the vehicle profiles and get your results. Note that these are not models, but based on real engine testing, which is why the list is a bit ideosyncratic---the emissions group tests whatever it can get its mitts on.
posted by bonehead at 8:00 AM on December 16, 2005

Ah. I see the problem. I would consider anything above the TLV/TWA to be a high level, that is above 5000 ppm, which is what most monitors are set to alarm at. The STEL is about 3%, which is the limit you can take for 15 minute periods. The IDLH, the escape-now level, is 4%.

Keep in mind that oxygen only needs to be displaced a couple of percent to be dangerously low. Normal atmosphere is 21.5%, below 19.5% is considered low oxygen. At a 2% or 3% displacement, you're getting into hypoxic conditions. The fact that narcosis is being induced at that point probably doesn't help either.

If I'm reading the literature right 5% (50,000 ppm) is the cross-over point at which blood no longer deacidifies. That's a very high level---you only get that at the bottom of silos and the like. As I said earlier, we've never seen more than twice ambient levels (600 ppm) at the base of fires.
posted by bonehead at 11:21 AM on December 16, 2005

Keep in mind that oxygen only needs to be displaced a couple of percent to be dangerously low.

I think you are mistaken in that. Maybe it's because I don't quite know what you mean by "displacement". Reducing the O2 content of air by 2 or 3% is not going to be a problem for most people.

The point in all those links I posted is that CO2 is toxic in and of itself, completely independent of O2 availability. To re-quote the doctor in my first link: And when the CO2 hits about 7% to 10% of your ambient air, you DO die. Even if the rest is O2. It isn't from lack of oxygen, it's from presence of CO2.
posted by Kirth Gerson at 12:22 PM on December 16, 2005

Reducing the O2 content of air by 2 or 3% is not going to be a problem for most people.

In practice, you're correct. Hypoxia symptoms start at about 18%, a reduction of 3% or so. At that point your reactions degrade and decisions become harder. Headaches are common too. The 19.5% is the minimum oxygen limit as defined by OSHA, the NFPA, the CLC, etc... which is when we switch to supplied-air respirators.

And I take your point that CO2 is acutely toxic at 7%, though I'd even lower that to somewhere between 4 to 5%, based on the blood deacidification data in some of your later references. I reiterate that that's an almost absurdly high level of carbon dioxide though. As I mention above, I'd consider anything above 0.05% too high.
posted by bonehead at 12:51 PM on December 16, 2005

Blargh. Sorry, anything above 0.5% is too high.
posted by bonehead at 12:52 PM on December 16, 2005

And I agree that it's rare that you'd encounter CO2 levels that high, although I have done so.
posted by Kirth Gerson at 1:45 PM on December 16, 2005

Cars are the real enemy. They are rarely a few feet away, wherever you may be. There's no escape!
posted by Leam Srehtorb at 5:42 AM on December 29, 2005

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