In munitions, pyrotechnic delay elements are used to time sequences of energetic events. For example, a hand grenade fuze must provide a reliable and safe interval between when the primer is struck (the grenade is released) and subsequent initiation of the main charge. As of 2022, the gasless delay compositions used in M201A1, M213, and M228 hand grenade fuzes still contain objectionable and problematic components such as potassium perchlorate (KClO4) and barium chromate (BaCrO4). Most military training was suspended at Camp Edwards (near Falmouth, Massachusetts) in the late 1990s because of groundwater contamination caused by the use of various munitions, including perchlorate-containing pyrotechnics. Additionally, it is current Department of Defense (DoD) policy to minimize the use of hexavalent chromium, a constituent of barium chromate. To reduce the risk of training interruptions and to avoid the expense of environmental remediation, pyrotechnic delay compositions free of perchlorate salts and chromate compounds are clearly needed. Therefore, the objective of this project was to confidently identify more sustainable pyrotechnic systems for use in M201A1, M213, and M228 fuzes.
This project involved concurrent activities at three different centers. To reduce the chance of selecting problematic replacements, an assessment of the potential toxicological and environmental effects of candidate materials was carried out at the U.S. Army’s Public Health Center, at Aberdeen Proving Ground in Maryland. Another part of this project involved the formulation of alternative pyrotechnic compositions and detailed studies of their combustion properties, and this work took place at the South Dakota School of Mines and Technology in Rapid City, South Dakota. The most promising alternatives were integrated and tested in actual M201A1 and M213/M228 fuze hardware at the U.S. Army’s Armaments Center (Picatinny Arsenal, New Jersey). Armaments Center personnel, having proposed the project, also coordinated the various activities described above.
In the subject design configurations (hand grenade fuzes), the most promising alternative pyrotechnics represent low hazards to both human health and the environment. Exposure is limited to manufacture and post-use degradation. Although the anticipated conditions of use (that is, no significant inhalation exposure) mean that additional toxicological studies are not needed at this time, such studies may become necessary, especially if inhalation exposure is found to be an issue.
Simple mixtures based on the Mn/MnO2 and W/MnO2 thermitic systems are promising alternative gasless delays. The combustion characteristics of the W/MnO2 system were thoroughly investigated. Combustion velocities ranged from 0.67-1.68 mm/s for 6.35 mm diameter open-air pellets, and from 1.62-4.61 mm/s when the compositions were combusted in 6.35 mm and 4.7 mm inner diameter aluminum and stainless steel housings. The maximum measured gas evolution was just 9.1 mL/g-composition. In other experiments, strontium molybdate was examined as a “drop-in” replacement for barium chromate in the traditional tungsten delay. Measured combustion velocities ranged from 1.36-29.87 mm/s in 4.7 mm inner diameter aluminum housings, and the maximum measured gas evolution was only 4.1 mL/g-composition.
Delay compositions containing manganese or tungsten, manganese dioxide, and powdered soda-lime glass (in some instances) were integrated with a newly developed titanium-based igniter system and were found to be effective in M201A1 and M213/M228 fuze hardware at cold, ambient, and hot temperatures.
Figure. An M18 smoke grenade rests on the ground during Integrated Training Exercise 2-19 at Range 220, Marine Corps Air Ground Combat Center, Twentynine Palms, California, on February 9, 2019. Smoke grenades, such as this M18, are fitted with M201A1 fuzes. (U.S. Marine Corps photo by Lance Cpl. Colton Brownlee. Public domain photograph; no known restrictions on publication or reproduction. The appearance of DoD visual information does not imply or constitute DoD endorsement.)
This project has advanced the state of the art in pyrotechnic delays and has already transitioned into a demonstration—ESTCP WP20-5045, called “Green” M213/M228 Fuze. ESTCP WP20-5045 will culminate in the demonstration of fully assembled M213 fuzes that contain “green” energetic subcomponents entirely free of lead, chromium, barium, and perchlorate. The results will be applicable to both M213 and M228 fuzes, which share a common delay element.