Everyday in factories around the world, people manufacture energetic materials at the commercial scale. Yet we do not witness a continuous stream of reports describing industrial tragedies at these facilities. Plants for the manufacture of energetic compositions are often purpose built with many layers of protection (LOP) built-in. Such facilities may be constructed in remote locations and with assets separated by large distances.
What is telling about explosive chemical manufacturing is the extent to which the operators possess a deep level of knowledge of their materials and processes. The explosives industry has at its fingertips a wide variety of tests that assay certain manifestations of sensitivity. There are many tests that assay for friction sensitivity and for shock sensitivity. Impact and electrostatic stimuli are also important dimensions not only for manufacture, but for use in the field.
For instance, a material with a high detonation velocity may have a large critical diameter, meaning that the packing density and bulk geometry must be sufficiently large for it to propagate a shock. Knowledge of impact sensitivity, shock sensitivity, or detonation velocity alone does not tell the whole story of the explosive.
There are several causes for this depth of knowledge. Easiest to see is the history of US explosives manufacture. There have been many spectacular industrial accidents going as far back as the revolutionary war. Much has been learned about manufacture and handling at a very high cost to lives and property. The explosives industry has had to learn to develop safe manufacturing practices to prevent the loss of life and business interruption.
Another motivating influence for explosives safety is perhaps less than obvious to outside observers. Over time, the US military has been revising and modifying its munitions designs and specifications. It is highly desirable that explosives and propellants provide maximum energy density for performance requirements, but at the same time be sufficiently insensitive to inadvertant stimulus so as to provide maximum safety for those handling the munitions.
The properties of military explosives- a major market driver- are highly specified by military procurement. The current library of explosive compositions have been highly refined through many years of evaluation and field testing. The effect has been that the compositions presently in the field are quite well understood in terms of their operational boundaries.
In addition to being driven by material specifications, manufacturing facilities and quality control systems are also driven by a selection process that is quite stringent. We see fewer explosive plant disasters today not only because the explosives are safer, but also because plants are managed better.
The lesson in this for fine chemical operators is that depth of knowledge of materials and reaction mixtures can be highly desirable and potentially very useful. In particular, an intimate understanding of the behavior and sensitivity of materials under process conditions as well as off-normal conditions can lead to safer plant operations.
Seems like a “No-Brainer”. But the fact is that the activity leading to such knowledge can be difficult, time consuming, and expensive to obtain. The push to get product out the door can be irresistable and the urge to cut corners can happen quietly and without fanfare. It is very easy for institutional knowledge to be lost in the struggle to maintain output and profitability.
Fine chemical manufacturers can be hobbled in their understanding in other ways. On the producers side or on the users side of fine chemicals, it is not unusual for chemists to specify methods of analysis that are familiar to them. NMR or GCMS or a variety of wet chemical methods set up on the benchtop are commonly used to set specifications and to validate certificates of analysis.
However, familiar methods of analysis tend to give profiles of familiar properties. Unfamiliar properties or contaminants may be invisible to any given method of analysis. A compound with a low threshold to decomposition or one that will exotherm vigorously and shed mass aggressively may reveal this attribute only through happenstance to an alert chemist.
What is especially interesting about explosives testing is the extent to which compositions are subjected to challenge tests. Rather than looking for a spectral signature, materials are subjected to a variety of stimuli in a manner that provides an unambiguous outcome. The card gap test for instance looks at the sensitivity of a composition to a standard stimulus that has been attenuated through a variable gap (set of spacers) of polymethylmethacrylate or air. Does it produce a hole in the witness plate or not?
There are people who go to work in nitroglycerin factories everyday knowing that they are working with a shock sensitive high explosive. Others may work in a lead styphnate factory filling primer cartridges by hand.
There are also people who go to work everyday in plants that have banned the use of diethyl ether or require peer review of even the simplest reaction they run in their fume hoods. The range of what is considered acceptable risk varies greatly.
Today, there is a mandate for IM- Insensitive Munitions. Here is the scenario- a TNT filled projectile is impacted by a large caliber projectile or shrapnel. There is a good chance the stimulus provided by the impacting body will initiate the TNT and cause the charge to explode, causing death or harm to those in the area. It is desirable to have high explosives that detonate or deflagrate only when properly initiated.
A major push is being made at government and industrial labs to produce explosive compositions that are insensitive to inadvertant stimulus, yet energetic enough to perform the task. One desired end of this activity is to phase out TNT in military explosives. The lack of US manufacturers of TNT is nearly as important a motivating factor as the sensitivity issues are. From the industrial hygiene side, some workers reportedly become sensitized to TNT, so the elimination of this toxicological dimension is desirable as well.
Green munitions are also part of a phase change in the munitions field. At first blush it seems silly to make explosive devices more environmentally friendly. However, explosive chemicals and their decomposition products can be widely dispersed in the environment as the result of warfare and training. The reduction of toxic residues can be considered a reduction in collateral damage.
Lamentations on Chemistry 