After the successful SERDP projects WP-2148 Development of Low-Toxicity Obscurant Material and WP-2405 Proof of Concept Novel Low-toxicity Obscurant, one issue remained before a transition to industry can take place. The obscurant performance at ambient and cold conditions is not, like at hot conditions, at the high-performance level when compared to hexachloroethane (HC) based obscurants. The objective of this project was therefore to improve the obscurant performance of compositions 15EM0281 and 15EM0282 at ambient and cold temperature conditions.

A root cause analysis (RCA) was performed that assessed the possible causes of the low performance at cold and ambient conditions. This RCA led to a design of experiments to gain insights into the possible cause(s). The RCA yielded that particle size and ingress of moisture were possible effects that may explain the observed differences in performance. To elucidate these effects, small scale experiments (5 and 10 gram scale) were executed with sub-scale grenades as well as thermogravimetric/differential scanning calorimetry measurements.

Exposing the novel obscurant mixtures to a temperature of 71°C seemingly improves the performance, compared to those compositions not conditioned at such a temperature. However, this effect seems to be ‘reversible’ and cannot be fully explained based on the small scale experiments. Effects were previously noticed with the full scale tests which cannot be appropriately mimicked at the small scale employed. The particle size distribution of the aerosol formed with the small scale tests is appropriate for a smoke screen and comparable with other formulations. Hence, other – at this point – unknown factors affect the performance of the novel obscurants. Based on the obtained results with the small scale experiments it can be unambiguously concluded that the ingress of moisture and the particle size distribution of the ingredients do not explain the differences in performance.

With a successful project, the Department of Defense has a visible obscurant candidate that has a reduced toxicity and a similar performance compared to HC. Several other benefits exist for the new sea salt compositions. These mixtures do not require the use of a solvent during production of the mix. This gives an easy method of preparation, resulting in no hazardous solvents, less waste and a reduction in time required to prepare the mixture. These mixtures are also quite robust; they do not require a tight tolerance on the percentages of ingredients in order for the smoke production to be successful. Finally costs of production are estimated to be at least at the same level and likely lower as those of the current smoke grenades. (Project Completion - 2021)