Waterjetting 37b - How safe is it?

We began looking into the use of water jets to deal with energetic materials (a group that includes, but is not limited to, explosives) at the beginning of the 1980's. One of the earliest questions dealt with the need to find the jet pressures at which the explosive materials would react to the impact of the water.

We produced a short video of that initial work, and with apologies for the degradation that occurs with time and the transfer of the material through different media, here is what I believe was the second report we made, after we had been told that just showing that jets could remove material without reaction was not sufficient.

Figure 1. Looking for the initiation of explosive.

Mrs. Vicki Snelson did the initial commentary with Dr. Paul Worsey developing the technology that we used to see how the explosive was reacting.

Part of the problem, we discovered, was the the jet could start the explosive burning (deflagration) without causing it to detonate, but that the succeeding flow of water would wash that burning material away from the surface. Looking at the surface afterwards did not, as a result, show any reaction signs, and we could not always fully see the contact area. As a result the design was changed, so that the explosive could be held in a small chamber flooded with inert gas. The driving system was changed, so that only water entered the chamber, and so we could determine, by examining the chemical composition of the gases in the chamber after the test, if any reaction had, in fact taken place. Paul explains the modifications.

Figure 2. The first modifications to the test equipment.

Waterjetting 37a - Removing Explosives

One of the major efforts carried out at the High Pressure Waterjet Lab at Missouri S&T during my tenure related to removing explosives and other energetic materials from different casings. The casings ranged in size from very small anti-personnel mines to the large rocket motors that carry objects into space. The first part of that program dealt with the factors relating to the removal of explosives from warheads. Initially we had to show that this was relatively safe, and we initially thought that we were done when we showed that the explosive did not react as we went up to and beyond the pressures needed to wash the explosives from the case.

"Oh, no!" we were told, "That is not enough, we need to know how safe it is!" Which meant we had to determine, for each explosive we were likely to find, the waterjet pressure at which it reacted. (i.e. went BANG!) This meant that we had to fire water jets at pressures that ultimately reached 10 million psi (at which point all the explosives tested got seriously annoyed) to cover the field of response.

Once that safety level had been established then we could determine the pressures required to wash out the munitions, and from that design a tool to carry out the washout. We called the first one, WOMBAT, and here is a short video showing it in being used to clean out a SPARROW warhead.

Figure 1. Description of a Washout

The program examined a number of different approaches for different munitions, and we worked with Wilkes University in PA to build a full scale washout facility for shells, that was installed at the Navy facility in Crane, IN - but I'll show that, and movies of the development of a capability to cut into sealed munitions, in later posts.

Waterjetting 36d - Going through more complex walls.

This is a short post illustrating an early stage in our development of a light-weight tool that could be carried into building rubble, after a collapse, and drill down through it to provide access for tools to search, without the danders of destabilizing the pile.

We illustrated the lack of vibration by placing a full glass of water on top of the first concrete block to be drilled. As Mr. Dorle, the graduate student who built the equipment explains, the tool cut through all material it is likely to encounter, while using a pump available at the local hardware store, and in a total envelope that fits into the back of a pickup.

Figure 1. Mr. Dorle describing his design for a waterjet cutting tool.

in later work the tool was made even simpler, since the rotary mechanism was the heaviest and most difficult to move with the lance it proved possible to remove it, and I'll post a video of one of those demonstrations shortly.