1995 Congressional Hearings
Intelligence and Security

                             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


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.