A Safer Form of Fertilizer?

April 28, 2013

A tragic accident, perhaps compounded by carelessness, led to a fire and explosion in a fertilizer plant in West TX on April 17.   (Just to clarify a point which was slightly confusing in the initial reports, ‘West’ is the actual name of the town.)  The news was somewhat overshadowed by the bombings at the Boston Marathon on April 15, but the disaster killed 14 people, injured many more,  and devastated the small town.  The plant apparently had stores of anhydrous ammonia (NH3), a gas, and ammonium nitrate (NH4NO3), a solid.  Both are very commonly used as components of fertilizers.  Ammonia is a strong irritant, and a health hazard, but doesn’t burn in air except in very high concentrations (roughly 15-25%).  Ammonium nitrate is also an irritant; however, it is also a powerful oxidizing agent, and can form explosive mixtures with many organic compounds.

In fact, ammonium nitrate has been used, mixed with fuel oil, to make bulk industrial explosives for routine use, because of its low cost.  It has also been a popular ingredient for improvised explosive devices (IEDs) and vehicle bombs, such as the one set off at the Murrah Federal Building in Oklahoma City in 1995.  Because of its potential for misuse, there are regulations concerning its storage and use, but these are apparently not always followed.  (It appears that the plant in West did not report its February inventory of 270 tons to the Department of Homeland Security, as the law requires.)

An article at the Gizmag site reports that Kevin Fleming, an engineer from Sandia National Laboratory, has developed a technique for compounding ammonium nitrate so that it can’t be used to make fuel-based explosives.

Knowing that in ammonium nitrate the ammonium ion is weakly attracted to the nitrate ion, and that the right chemical reaction can pull them apart, Fleming decided to look for a compound they would rather cling to that could be added to the ammonium nitrate. He tried several materials, including iron sulfate, a readily available compound discarded by the ton from steel foundries.

If someone attempts to mix fuel into the ammonium nitrate / iron sulfate mixture, they will end up with ammonium sulfate and iron nitrate, neither of which will form an explosive mixture.

The addition of iron sulfate does not degrade the usefulness of the fertilizer; in fact, it probably makes it slightly better for environments with alkaline soils.  Adding iron to the soil may also incrementally improve the iron content of vegetable crops.

Since iron sulfate is cheap — it’s a waste product from steel production — this technique might be an economical way to reduce the risk of explosions, accidental or otherwise.

Update Monday, 29 April, 22:16 EDT

Here is the original Sandia Labs information release.  Their server appears to have been down last  night.

Subterranean Rumblings

April 7, 2013

Especially in the winter months, first time visitors to New York City are often bemused by the sight of plumes of steam rising from manholes in the street (sometimes surmounted by jolly red-and-white “smokestacks”).  Where do they come from?  Are they byproducts of some subterranean “dark satanic mills”, or perhaps a covert entrance to Saruman’s workshops at Isengard?   Actually, they come from the Con Edison steam distribution system,which distributes steam from seven generating plants through underground pipes to most of Manhattan south of about 90th Street.  [Coverage map PDF]  The steam is used to provide heat, hot water, and other services; it serves around 100,000 commercial and residential establishments with more than 13.5 million tons of steam every year.  Since about 50% of the steam is produced as a by-product of electricity generation, the system as a whole is more efficient than individual building heating and hot water plants.  The system, the first parts of which went into service in 1882, works fairly well, though there have been some spectacular failures in the aging infrastructure, notably the 2007 explosion at 41st Street and Lexington Avenue, which left a crater in the street 35 feet wide and 15 feet deep.

Here in Washington DC, we have our own peculiar sub-surface activity: our manholes do not spout steam, but do occasionally explode.  Natural gas has been suspected as a cause of these explosions, but hard evidence for this has been scarce.  Now, the ScienceNOW news service of the AAAS reports that researchers have found high methane concentrations in the city, and very high concentrations in manholes.

Researchers who mapped methane concentrations on the streets of the nation’s capital found natural gas leaks everywhere, at concentrations of up to 50 times the normal background levels, they reported here last week at a meeting of the American Physical Society. The leaking gas wastes resources, enhances ozone production, and exacerbates global warming—not to mention powering the city’s infamous exploding manholes.

Methane [CH4] can come from a variety of sources, including landfills, swamps, cattle flatulence, and oil/gas production.  It is also the principal constituent of natural gas.  It is potentially an important source of global warming, since it is more than 20 times more potent as a greenhouse gas than carbon dioxide [CO2], the usual suspect.  The research team, headed by Robert Jackson of Duke University, suspected that natural gas leaks might be contributing to increased methane concentrations in the atmosphere; the results confirmed their suspicions:

… they drove along every street in the District of Columbia and regularly sampled the air, mapping the concentration of methane over a period of 2 months. They found thousands of places with air concentrations significantly above the 2 parts per million background level typically found in cities, with some areas as high as 100 ppm.

Methane itself is non-toxic and odorless (the gas company adds a chemical, typically a thiol like tert-butyl mercaptan, to make the gas stink); however, methane can promote the formation of ozone, which is a respiratory irritant.

The research team got more striking results when they sampled methane concentration in manholes.  In some locations, they detected methane concentrations of 100,000 ppm (or 10%).  My well-worn Handbook of Chemistry and Physics gives (approximate) explosive limits for methane / air mixtures at 5% and 15%, so the detected values are well within the danger zone.  The team suspects corroding iron gas distribution mains as the source of the leaks.  There are an average of 38 “manhole incidents” per year in Washington, so something is clearly amiss. (The same researchers have some similar data from Boston.)

It is of course sort of interesting to discover what may be causing incidents like exploding steam pipes or manholes, but these incidents reflect a larger issue.  There is a great deal of very old infrastructure in the US. much of which has not received very much in the way of maintenance.  (As another, unrelated, example, in August 2007, a highway bridge carrying Interstate 35-W across the Mississippi River in Minneapolis collapsed.)  For years, the American Society of Civil Engineers, has issued an annual report card on the parlous state of the nation’s infrastructure; it does not make for encouraging reading.

Interview with James Randi

March 28, 2013

I’ve written here before about James Randi, the retired professional magician and skeptic of the occult, and his  James Randi Educational Foundation, which investigate claims of paranormal, supernatural, and occult  ideas.

The self-described “News for Nerds” site, Slashdot, has an interview with Randi, in which he answers questions submitted by readers,   As one might expect, the discussion focuses on the work, by Randi and the Foundation, to combat irrational and magical thinking.  It’s a brief but entertaining read.  The page also contains comments from Slashdot readers, which are worth glancing through: there are some insightful ones, though there is, as usual, a lot of drek as well.

Planck Observatory Looks Back in Time

March 21, 2013

Back in 2009, I posted a couple of notes here about the European Space Agency’s [ESA] Planck Observatory, The observatory operates in the microwave part of the electromagnetic spectrum, and is intended to make the most precise measurements yet of the Cosmic Microwave Background, a faint remaining echo of the aftermath of the Big Bang.  At the time I wrote, the spacecraft had just gotten ready to work, having reached its normal operating temperature of 0.1° K (-273.05° Celsius), just above absolute zero (0°K).

According to an article at the BBC News site, the Planck has now completed a 15-month sky survey, and the ESA has released a map of the results.

A spectacular new map of the “oldest light” in the sky has just been released by the European Space Agency.

Scientists say its mottled pattern is an exquisite confirmation of our Big-Bang model for the origin and evolution of the Universe.

Although the data broadly confirm the “Big Bang” model for the formation of the Universe, they do suggest some refinements from previous knowledge.  The Universe appears to be slightly older, at 13.82 billion years, that previously thought, by about 50 million years.  This indicates a slightly slower rate of expansion than previously calculated.  The breakdown of the Universe’s composition also works out a bit differently,   Based on the Planck results, there is a bit more matter (both ordinary and dark matter) than previous.y thought, and a little less dark energy.   The comparative figures are:

Component Previous Post Planck
Normal Matter 4.5 % 4.9 %
Dark Matter 22.7 26.8
Dark Energy 72.8 68.3

The Planck data have also confirmed some small anomalies that were previously noted in the data from NASA’s Williamson Microwave Anisotropy Probe (WMAP).  According to the theory, the differences in the level of background radiation (represented by the color “mottling” of the map) correspond to differences in the density of matter in the early Universe.

Cosmic Microwave Background

Cosmic Microwave Background (from Planck)
Image: ESA/Planck Collaboration

In the CMB map, above, the lower half of the image seems to be slightly warmer (orange / red) than the upper half; there also seems to be a cool spot (blue) just below and to the right of the center.  The reason for these anomalies is not known; they may hint at some new refinements to the underlying physics, or perhaps result from another, unknown microwave source.  Taken as a whole, though, the data seem to support the current models of the development and expansion of the early Universe.

Ars Technica also has an article on these results.

Happy Pi Day, 2013

March 14, 2013

Today, March 14, is one of the days that is sometimes celebrated as “Pi Day”, in honor of the best-known irrational and transcendental number, the ratio of the circumference of a circle to its diameter, usually written as the Greek letter π (pi).  The date, 3/14, is chosen because the approximate value of π is 3.14159265…   Legend has it that the value was named π because pi is the first letter of the Greek word “περίμετρος”, meaning perimeter.

The New Scientist reports that this year, to observe Pi Day, Professor Marcus du Sautoy of the University of Oxford is sponsoring Pi Day Live, a project to “crowd source” the calculation of π (pi).  The value has, of course, alreay been calculated to trillions of decimal places; because it is an irrational number, it cannot be represented exactly by any finite decimal number.  (Pi is transcendental, also, of course.)  Pi Day Live is suggesting some relatively easy methods of getting an approximate value for π, including Buffon’s Needle.  I mentioned Buffon’s Needle in a Pi Day post back in 2010.  The New Scientist headline calls it an “ancient” method, which I think is a bit over the top for something described in the 18th century.

That earlier Pi Day post also tells a related story, of the Indiana state legislature’s attempt to set the value of pi by law, one of the all-time great accomplishments of legislative lunacy.

Finally, take a thought today for 134th anniversary of the birth of Albert Einstein.

Update Thursday, 14 March, 15:35 EDT

I’ve just noticed that there is a rendering error (at least in Firefox) on the “Find Pi” page I linked above.  The equation for the estimated value of pi is a bit garbled (where it reads 2L\over xp; the correct equation (using the “Find Pi” variable names) is:

\pi = \dfrac {2 L}{x p}

I’ve dropped the site a note with the correction.

DEET Resistant Mosquitoes

February 25, 2013

Most readers, I’m sure, are aware that mosquitoes are a transmission vector for a number of rather nasty diseases, including malaria, yellow fever, equine encephalitis, and dengue fever.  The standard advice, in regions where mosquitoes are common, is to keep one’s skin covered, to the extent possible, and to use insect repellent liberally.  One of the most common active ingredients in repellents is a chemical usually referred to as DEET (more formally as N,N-Diethyl-meta-toluamide or [IUPAC] N,N-Diethyl-3-methylbenzamide), an oily compound originally developed by the US military after the experience of jungle warfare in World War II.   Various ideas have been suggested to explain why DEET works; today, the consensus seems to be that insects just don’t like the smell.

However, a report at the BBC News site suggests that DEET’s effectiveness can be reduced because mosquitoes can adapt to it.  One type of adaptation is genetic.  There are always some individual insects that are less susceptible to DEET than average, and heavy use of the repellent creates evolutionary selection pressure favoring that lack of sensitivity.  (This is parallel to the evolutionary process leading to the development of antibiotic-resistant bacteria, or of herbicide-resistant weeds.)   This is a process that takes some time to occur, though mosquito generations are of short duration.

Some recent research indicates that there is another, shorter-term form of resistance that occurs.  Researchers at the London School of Hygiene and Tropical Medicine studied the effect of DEET on Aedes aegypti mosquitoes, which carry dengue and yellow fevers.  The mosquitoes were initially given the opportunity to feed from a human arm which had been covered with DEET; the repellent did, in fact, repel them.  However, when the same mosquitoes were presented with the same opportunity a few hours later, the repellent was significantly less effective.

To try to understand what was happening, the researchers measured electrical activity in the insects’ antennae (the location of the olfactory receptors).  Somehow, the first exposure to DEET de-sensitized the mosquitoes, so that their olfactory response was diminished.  According to Dr. James Logan,

We were able to record the response of the receptors on the antenna to DEET, and what we found was the mosquitoes were no longer as sensitive to the chemical, so they weren’t picking it up as well.

There is something about being exposed to the chemical that first time that changes their olfactory system – changes their sense of smell – and their ability to smell DEET, which makes it less effective.

The research paper [PDF available] has been published at the Public Library of Science, in the journal PLoS One.

More work will be needed to determine how long this short-term effect lasts, and whether it occurs in other species of mosquito.   Using repellents containing DEET is still a lot better than using nothing, but understanding these effects may help us develop even more effective protection.

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