Statement of J. Edmund Hay U.S. Bureau of Mines Research Physicist Pittsburgh Research Center before the Committee on the Judiciary U.S. House of Representatives June 13, 1995 Mr. Chairman, members of the Committee, my name is Ed Hay. I am a Research Physicist with the Fires, Explosions, and Explosives Group of the Pittsburgh Research Center of the U.S. Bureau of Mines. I am also chairman of the National Fire Protection Association's Technical Committee on Explosives and a member of Committee F-12 (Security Systems) of the American Society for Testing and Materials. Since its inception in 1910, the Bureau has been charged with the responsibility of performing research to improve safety in the mineral industries, particularly with regard to accidental explosions. In pursuit of this mission, the Bureau has a long history of research, testing, and test development related to the explosive behavior of chemicals that are either explosive ingredients or that have similar properties. This especially includes ammonium nitrate, which is not only a major ingredient of virtually all nonmilitary explosives, but which has a long history of involvement in accidental explosions. I would like to offer for you today some observations relative to two areas of the proposed legislation of H.R. 1710, namely: o The proposal to render common chemicals used in manufacturing inert as explosive ingredients and o The subject of explosive taggants. Ammonium nitrate is the least expensive and most widely available used ingredient in commercial explosives. It is available in two basic forms: o One intended for use as a blasting agent ingredient, and o One intended for use as fertilizer. The principal difference is the porosity of the granules, or "prills." It is probable that any technical modification of the explosive-grade material to diminish its usefulness to terrorists would have equally deleterious effects on its legitimate use. The only practical solution to the control of explosive-grade ammonium nitrate, therefore, appears to be outright legislative control of its availability. Thus, I prefer to confine my remarks to agricultural-grade ammonium nitrate. In this regard, there are two important considerations. The proposed modification of the product should: o Render it useless to the potential terrorist, and o Cause no severe hardships for the legitimate user. It is well established that dilution of explosives diminishes their detonability. This fact has been, and continues to be, exploited. There is little question that it can be applied to ammonium nitrate and its mixtures. I use the word "diminish" rather than Eliminate," because the detonability of a substance depends both on the quantity of the substance under consideration and the intensity of the stimulus to which it is subjected, and it is thus not a uniquely determinate property. The object is to determine a diluent and a level of dilution that minimizes its usefulness as an explosive while retaining its benefit as a fertilizer. This must be done with great care, as evidenced by an attempt in Germany in the 1920's to add 45% ammonium sulfate to ammonium nitrate to make it inert. This reduced the nitrogen content by 18%, yet this combination still produced the greatest single historical disaster involving ammonium nitrate in which the German town of Oppau was level led. There have been several proposals to incorporate various ingredients to reduce detonability. Although I do not claim to know all of them, I have noticed that, in some instances, the data supposedly substantiating their effectiveness are based on tests with rather small charge sizes and initiating stimuli. Such attempts can be misleading if not validated by appropriate testing. The quantity of product and number of legitimate users of agricultural ammonium nitrate are very large. Many of the users may be presumed to be vulnerable to the economic and other impacts of degradation of an essential commodity. Bearing this in mind, the Bureau of Mines has been considering the potential dilution of ammonium nitrate by a chemical that is itself a high nitrogen fertilizer, namely urea. Urea contains 46% nitrogen, while ammonium nitrate contains 34%. Our data indicate that, at sufficient levels of dilution, the detonability of ammonium nitrate is greatly reduced. We look forward to other studies on the potential of urea and other diluents. One might ask why the simple replacement of ammonium nitrate by urea in this application is not completely satisfactory. The answer is that, in certain widely prevalent agronomic applications and conditions, urea loses a significant fraction of its nitrogen before it is absorbed into the soil and is thus somewhat less cost-effective. Further assessment of the agricultural aspects of this issue, coupled with a review of the detonation aspects, is warranted by appropriate experts. Another important point is that ammonium nitrate, or other potential explosive ingredient, should not be readily separated from the diluent. Urea is normally sold in a form in which it is physically practically indistinguishable from ammonium nitrate. It also has very similar solubility in water, so that neither the physical separation process nor methods based on differential solubility are practical for separating the two ingredients. A careful review of all possible separation schemes needs to be conducted before such an approach would be considered for final implementation. I should note here that we are considering a simple mechanical mixture of the individual prills of the two substances, not a mixture in which the prills themselves would be composed of a more intimate mixture. The proposal to use urea may seem paradoxical to those who are aware that, in concentrations below 20%, the addition of urea actually increases the detonability of ammonium nitrate, but at higher concentrations this effect is reversed. Once an explosive mixture reaches the condition at which the fuel content exceeds that which the available oxygen can oxidize, further additions of fuel diminish the detonability. In ammonium nitrate/urea, this occurs at 20% urea. Thus, a nondetonable mixture could not be made detonable simply by addition of fuel, as in the case of pure ammonium nitrate. Existing data on the effect of urea pertain only to small-diameter charges. These data need to be extended to much larger charge sizes and much larger initiating stimuli to establish a level of dilution at which detonation would require such a large quantity of material and/or such a large stimulus as to be beyond any practical limit. This applies to any attempted diluent, not just urea. It may be objected that ammonium nitrate could still, with patient effort, be extracted from the mixture and used. I would respond that this is true. It is equally true that with patient effort explosives can be made from chemicals that are so common that restricting their availability is beyond the bounds of reason. In other words, there is no absolute solution to the problem. We can only strike a balance between making life more difficult for the terrorist and making life too difficult for ourselves. It has been said that urea seems to be a strange choice because it was used in the World Trade Center Bombing. Although true, the urea in this case was combined with nitric acid, and if one postulates the availability of nitric acid, the opportunities for making explosives are so great that I would not attempt to catalog them. A key point here is that the level of effort required for the potential terrorist should increase with the magnitude of the intended explosion. At present, disaster comes ready-made, since ammonium nitrate is detonable in its own right without any added fuel. The fact that the explosive energy release of pure ammonium nitrate is less than one-half that of the normal mixture with fuel oil is of little comfort. All that is required to detonate a storage pile, truckload, train load, or shipload is the insertion of a sufficiently large explosive booster. This scenario at least would be impossible if the ammonium nitrate were diluted at the point of manufacture. As I indicated before, at this point the precise level of dilution required is unknown. There is considerable evidence that the detonability of a substance is strongly correlated with the energy that it would release if detonated, a value that is easily calculated. There is no known instance of a substance detonating that has an energy of less than about 200 calories per gram. An adequate margin of safety would probably be about 150 calories per gram. The level of dilution corresponding to this is about 58% urea. This, however, should be verified experimentally. The Bureau of Mines has previously been involved in programs of technical evaluation of the feasibility of explosive tagging, and our experience in this area is at your disposal. And, of course, we are willing to produce any assistance that we can to the Department of Justice, the Bureau of Alcohol, Tobacco and Firearms, and other Government agencies in studying taggants and the feasibility of rendering common chemicals inert. Thank you, Mr. Chairman, for the opportunity to testify before you and for your attention. The Bureau of Mines remains ready to assist you with those technical matters in which we have expertise. I am prepared to respond to any questions that you may have.