(Note: the material must not be tamped or otherwise compressed. Insensitive granular materials are easily "deadpressed," and this must be avoided. The light tapping on the side of the pipe will result in what is known as "poured" density in explosives industry testing.)
Place the booster in the top of the pipe, with the initiation system inserted. Attach the continuous-detonation velocity probe to the booster. The initiation system may be of the electric or shock tube variety.
For underwater testing, enclose the entire unit in a waterproof plastic wrapping. Attach a strong cable ("airplane" cable should be suitable) to the hole in the outer corner of the witness plate, and secure the other end of the cable to an anchorage on the shore of the test pond.
Fire the charge, and record the detonation trace and the appearance of the witness plate, if recovered.
To ensure accuracy and consistency of results, the test should be repeated three times.
Detonable fertilizer mixtures will be indicated by a continuous-detonation velocity probe trace that shows a sustained, steady-state or an increasing velocity from the booster area to the end of the pipe, and/or a retrieved witness plate that has a hole punched through it, or has deep cupping.
Nondetonable mixtures will be indicated by a continuous-detonation velocity probe trace that shows a decreasing velocity, or velocity falling to zero, and/or a retrieved witness plate with no deformation or only slight denting. Borderline results should be interpreted as detonations, since this may indicate that a slightly larger charge would sustain detonation.
The above test, although it may be difficult to administer and may even be impossible to run at all test sites, should determine definitively whether or not a particular fertilizer mixture poses a potential threat in the hands of a person attempting to construct a destructive device. This test should have to be run only one time (in triplicate, as noted above) on each "family" of fertilizer materials.
Although some may consider that a larger mass of material might sustain a detonation even though the material was nondetonable in the test with a 12-inch-diameter pipe, the committee believes that potential explosive mixtures of this low level of sensitivity pose little threat to the public.