posted December 04, 1999 05:37 PM            

"Chemical & Engineering News, July 24, 1995

"Government, Industry Efforts Yield Array Of Tools To Combat Terrorism." by A. Maureen Rouhi,
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The Oklahoma City blast prompted a second look at a patent awarded 30 years ago to Samuel J. Porter, a hazardous chemicals consultant from Woodbridge, Va. (C&EN, May 29, page 6). The patent claims addition of 5 to 10% by weight di- or monoammonium phosphate will prevent ammonium nitrate fertilizer from exploding.

Four victims of the Oklahoma City bombing have filed a lawsuit against ICI Explosives. The Dallas-based company is a major producer of ammonium nitrate industrial explosives. But it also produces fertilizer-grade ammonium nitrate at its operations in Joplin, Mo., and ships it to agricultural cooperatives for distribution to farmers in Missouri, Kansas, Oklahoma, Arkansas, Iowa, and Texas. The lawsuit claims ICI Explosives should have incorporated additives such as those mentioned in Porter's patent to render the ammonium nitrate fertilizer it produces less explosive (C&EN, May 22, page 11).

E. I. (Joe) Brawner, ICI Explosives president, has told employees: "Our contact with investigating authorities has not resulted in any indication that ammonium nitrate fertilizer produced by ICI was involved in the criminal act in Oklahoma City." Nevertheless, last month, the company carried out experiments to test the claims in the Porter patent. The company prepared "desensitized" ammonium nitrate according to the patent instructions. Then it called on an independent consulting firm that investigates engineering or scientific failures to test the material. The consulting firm, Failure Analysis Associates, Menlo Park, Calif., tested 10-gal charges at a site near Phoenix.

The results, which were recorded on videotape, show neither diammonium phosphate, monoammonium phosphate, nor calcium carbonate eliminates the explosiveness of ammonium nitrate. ICI Explosives suggests the 1968 patent "covers explosions on such a small scale as to make[ it] irrelevant to the terrorist issue." The importance of the scale of testing is reinforced by Peter G. Urben, editor of "Bretherick's Handbook of Reactive Chemical Hazards." He tells C&EN: "Because terrorists now use 1,000-lb charges or larger - and the larger [the charges] are, the more likely they will explode, especially if confined - very large detonation tests will be required to suggest inhibition."

Besides, a simple countermeasure exists, points out Kay R. Brower, professor of chemistry at the New Mexico Institute of Mining & Technology, Socorro. The ammonium phosphate can be removed easily from an aqueous solution by reaction with calcium nitrate, to give even more ammonium nitrate:

(NH4)2HPO4 + Ca(NO3)2 -> 2 NH4NO3 + CaHPO4
The calcium salt precipitates, leaving dissolved ammonium nitrate, which can be recovered by evaporation.

But worse, the heat released from detonation of a mixture of ammonium nitrate and ammonium phosphate is up to 60% greater than that from ammonium nitrate alone, Urben says. He explains that ammonium phosphate acts as a fire retardant for cellulosics by forming a crust that prevents oxygen from reaching the fuel. But in an explosion or deflagration, oxygen already is intimately mixed with the fuel, and the ammonium in ammonium phosphate serves as additional fuel.

Ammonium sulfate, another proposed desensitizer, presents a similar scenario. In a recent article in Chemical Health & Safety [2(3), 22 (1995)], retired organic chemist Leslie Bretherick recalls how, in 1921, a 4,500-metric-ton stockpile of ammonium nitrate containing 45% ammonium sulfate exploded at a chemical factory in Oppau, Germany. The accident killed 600 people, injured 1,500 more, and left 7,000 homeless. The heat released by the reaction of a 2:1 mixture of the salts is also greater than that from ammonium nitrate alone.

Another potential additive is potassium nitrate, says retired chemist Carl Boyars, formerly a senior scientist at the Naval Surface Warfare Center, Silver Spring, Md. Boyars explains that the likelihood of ammonium nitrate's exploding when shocked by a booster explosive is higher each time the ambient temperature cycles through 32 °C. At this temperature, the compound undergoes a phase change. Because the porosities of the phases are substantially different, the porosity of the ammonium nitrate granules increases with each cycle, making the material more sensitive to detonation. If potassium nitrate is added to ammonium nitrate to form a solid solution, the phase change does not occur, and the material is less sensitive to detonation. Boyars says military explosive compositions incorporating ammonium nitrate cocrystallized with 10% potassium nitrate were less sensitive to detonation than similar compositions with plain ammonium nitrate. He is not aware of any follow-up work on this approach to desensitizing ammonium nitrate."

Interesting, huh? I especially like how the additives are all totally "harmless" and thus unmonitored. And cheap to boot. If you can add 40% more weight to your explosives and get almost 2x the power, go for it! Also, the thermal cycling to increase sensitivity would be easy to do, just have a warm oven going, put in a tray of AN, let it warm up for 15 minutes, take it out and let it cool off, then put it back in. Do that about 5 times and your set.

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"The knowledge that they fear is a weapon to be used against them." www.50megs.com/nbk2000

posted December 05, 1999 03:20 PM            

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-Knowledge is power, power leads to corruption, corruption is a crime, crime doesn't pay. So if you know to much you will go broke!!!

posted December 09, 1999 06:57 AM            

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"The knowledge that they fear is a weapon to be used against them." www.50megs.com/nbk2000

posted December 09, 1999 03:16 PM            

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-Knowledge is power, power leads to corruption, corruption is a crime, crime doesn't pay. So if you know to much you will go broke!!!

posted December 09, 1999 10:35 PM            

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-Knowledge is power, power leads to corruption, corruption is a crime, crime doesn't pay. So if you know to much you will go broke!!!