Flyer within the plume of an open burn

DoD ammunition plants and demilitarization facilities have long relied on open burning (OB) of propellants, open detonation (OD) of explosives, and static firing (SF) of rockets to destroy excess, obsolete, or unserviceable munitions, and energetics materials. These practices are employed as a means to dispose of hazardous materials, manufacturing wastes, and off-specification ordnance where recycling, neutralization, and enclosed destruction pose too great a risk to the material and equipment handlers and are generally not allowed by Department of Transportation regulations.

Increasing limitations on OB/OD are based on human health risk assessments and include evaluation of risks from airborne exposure to emissions generated from OB/OD which may include hydrocarbons, metals, hydrochloric acid (HCl), perchlorate, volatile organic compounds (VOCs), semi-VOCs, and PM₁₀ and PM_2.5 particulates.

Flight path of sampling drone

Emission Factors are developed from limited open atmospheric testing as well as from small-scale OB/OD chambers known as a BangBox®. Questions persist on the applicability of chamber test results when extrapolated to determine open air, full-scale OB/OD exposures. The reliability of earlier measurements was impacted by rapid plume dispersion, short event durations, heterogeneous emission concentrations, long plume life, soil entrainment, and explosive safety restrictions. An improved method for determining the potential for exposure was needed.

SERDP has supported multiple studies to develop field measurement technologies for measuring OB/OD emissions, each a one-year project (WP-1672, WP-2153, and WP-2233). Research teams conducted sampling campaigns at Tooele Army Depot to test the feasibility of direct-plume measurements using a tethered balloon-lofted sampler (“Flyer”), optical remote sensing for particulate matter, and a NASA UAS Hexacopter Unmanned Aerial System.

Plumes were characterized to determine overall emissions and calculate Emission Factors. This work represents the first emission sampling of soil-covered metal-cased ordnance detonations in the open atmosphere and determined the first PM_2.5 emission data for OD operations. Repeated detonations under identical conditions resulted in a wide variability between detonation events and within detonation plumes. However, the drone was capable of achieving much better results than with the tethered balloon for both chemical constituent and particulate matter sampling.

While more field demonstrations will be necessary, it is expected that DoD will now be able to take advantage of this technology to improve calculated Emission Factors and ultimately determine methods for reducing overall human and ecological exposure.