When the AN-M8 handheld smoke grenade is functioned, it produces a hexachloroethane (HCE) based smoke. This smoke can cause a number of medical problems that range from cough and difficulty breathing to chemical pneumonitis, pulmonary edema, adult respiratory distress syndrome, severe liver problems and death. These health issues pose a threat to the health of the war fighters that are exposed to this smoke during training and combat. The objective of the project was to demonstrate a pyrotechnic formulation at a laboratory scale that can match or exceed the opacity, duration of obscuration and area of coverage of the smoke produced by an AN-M8 handheld grenade.
A variety of pyrotechnic compositions were investigated for their viability as replacements for HCE based obscurants. The investigations included combustion modeling, ingredient and composition thermal compatibility and sensitivity to significant impact, friction and electrostatic discharge events. Candidates were screened through the combustion of small samples (less than ten grams) via open burning and combustion in a 100 cubic foot chamber to determine smoke density and analyze for toxicity of combustion gases and particulates.
Compositions containing divalent zinc and copper oxidizers combined with ammonium chloride were deemed to be thermally incompatible. Compositions containing sodium nitrate, silicon powder and polydimethylsilicone binder improved in performance as the ratio of silicon powder to silicone polymer decreased and the total fuel content increased. Compositions containing boron potassium nitrate igniter blended with halide salts (cesium, potassium and ammonium) were studied in greatest detail. Solids produced from the combustion of the specific compositions selected for study were not totally dispersed in aerosol form; significant solid slag formation was observed. Thus, smoke density efficiency was only one quarter of that of the HCE containing baseline. The addition of lower levels of the halide salt coolant to the boron potassium nitrate igniter may improve overall obscurant efficiency. The overall toxicity of combustion gases and particulates is lower for boron potassium igniter blended with cesium or potassium chloride relative to the HCE baseline obscurant.
Informative, reproducible methods were developed for characterization of the smoke density of particulate aerosols, and the determination of particulate concentrations, particulate particle size distributions as well as the chemical composition of the particles and toxic gases produced from baseline and candidate obscurants. Hazards for processing and testing the obscurants were well defined and controlled. Although the specific formulations tested did not perform as well as the HCE baseline, formulation variants were identified which should have improved performance.