Characterization of M4 carbine rifle emissions with three ammunition types

Chemistry and lung toxicity of particulate matter emitted from firearms

Smoke emissions produced by firearms contain hazardous chemicals, but little is known if their properties change depending on firearm and ammunition type and whether such changes affect toxicity outcomes. Pulmonary toxicity was assessed in mice exposed by oropharyngeal aspiration to six different types of smoke-related particulate matter (PM) samples; (1) handgun PM, (2) rifle PM, (3) copper (Cu) particles (a surrogate for Cu in the rifle PM) with and without the Cu chelator penicillamine, (4) water-soluble components of the rifle PM, (5) soluble components with removal of metal ions, and (6) insoluble components of the rifle PM. Gun firing smoke PM was in the respirable size range but the chemical composition varied with high levels of Pb in the handgun and Cu in the rifle smoke. The handgun PM did not induce appreciable lung toxicity at 4 and 24 h post-exposure while the rifle PM significantly increased lung inflammation and reduced lung function. The same levels of pure Cu particles alone and the soluble components from the rifle fire PM increased neutrophil numbers but did not cause appreciable cellular damage or lung function changes when compared to the negative (saline) control. Penicillamine treated rifle PM or Cu, slightly reduced lung inflammation and injury but did not improve the lung function decrements. Chelation of the soluble metal ions from the rifle fire PM neutralized the lung toxicity while the insoluble components induced the lung toxicity to the same degree as the rifle PM. The results show that different firearm types can generate contrasting chemical spectra in their emissions and that the rifle PM effects were mostly driven by water-insoluble components containing high levels of Cu. These findings provide better knowledge of hazardous substances in gun firing smoke and their potential toxicological profile.

Exposure to lead-free frangible firing emissions containing copper and ultrafine particulates leads to increased oxidative stress in firing range instructors

Background

Since the introduction of copper based, lead-free frangible (LFF) ammunition to Air Force small arms firing ranges, instructors have reported symptoms including chest tightness, respiratory irritation, and metallic taste. These symptoms have been reported despite measurements determining that instructor exposure does not exceed established occupational exposure limits (OELs). The disconnect between reported symptoms and exposure limits may be due to a limited understanding of LFF firing byproducts and subsequent health effects. A comprehensive characterization of exposure to instructors was completed, including ventilation system evaluation, personal monitoring, symptom tracking, and biomarker analysis, at both a partially enclosed and fully enclosed range.

Results

Instructors reported symptoms more frequently after M4 rifle classes compared to classes firing only the M9 pistol. Ventilation measurements demonstrated that airflow velocities at the firing line were highly variable and often outside established standards at both ranges. Personal breathing zone air monitoring showed exposure to carbon monoxide, ultrafine particulate, and metals. In general, exposure to instructors was higher at the partially enclosed range compared to the fully enclosed range. Copper measured in the breathing zone of instructors, on rare occasions, approached OELs for copper fume (0.1 mg/m³). Peak carbon monoxide concentrations were 4–5 times higher at the partially enclosed range compared to the enclosed range and occasionally exceeded the ceiling limit (125 ppm). Biological monitoring showed that lung function was maintained in instructors despite respiratory symptoms. However, urinary oxidative stress biomarkers and urinary copper measurements were increased in instructors compared to control groups.

Conclusions

Consistent with prior work, this study demonstrates that symptoms still occurred despite exposures below OELs. Routine monitoring of symptoms, urinary metals, and oxidative stress biomarkers can help identify instructors who are particularly affected by exposures. These results can assist in guiding protective measures to reduce exposure and protect instructor health. Further, a longitudinal study is needed to determine the long-term health consequences of LFF firing emissions exposure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00471-0.

Comprehensive characterization of firing byproducts generated from small arms firing of lead-free frangible ammunition

Following the introduction of lead-free frangible ammunition in United States Air Force small arms firing ranges, Combat Arms instructors have routinely reported experiencing adverse health symptoms during live fire training exercises, including sore throat, cough, and headache. Previous studies have found that these symptoms occur despite occupational exposure limits not being exceeded. To better characterize the potential source and mechanisms for health symptoms, a comprehensive characterization of the physicochemical properties of gases and aerosols emitted during the firing of the M9 pistol and M4 rifle using lead-free frangible ammunition was completed. Weapons were fired within a sealed chamber using a remote firing mechanism. A suite of direct-reading instruments and collection-based analytical methods were used to determine the composition of the emissions. Emissions were dominated by carbon monoxide and ultrafine particles. Other prevalent gases included carbon dioxide, ammonia, formaldehyde, hydrogen cyanide, and nitric oxide when measured using Fourier-transform infrared spectroscopy. An electrical, low-pressure impactor showed that, on average, the count median diameter immediately after firing was 36 ± 4 nm (n = 10 rounds) and 32 ± 3 nm (n = 14 rounds) for the M9 pistol and M4 rifle, respectively. Analytical methods were used to determine that emitted particles were primarily composed of soot, copper, and potassium, with trace amounts of calcium, silicon, sodium, sulfur, and zinc. Results from this research confirm prior work and expand upon the characterization of emissions generated from firing lead-free frangible ammunition. By employing multiple methods to measure and analyze data we were able to quantify both total and respirable particle fractions and determine particle morphology and composition. Characterization of the emissions provides insight into potential exposure risks that may lead to the development of adverse health symptoms allowing for the development of strategies for risk mitigation.

Exposures to lead during urban combat training

Lead exposure is still a major concern for occupations that regularly train or work with firearms, such as law enforcement and military personnel. Due to the increasing number of women of fertile age in such professions, there is a strong incentive to monitor lead exposures during firearms training. Personal air sampling was performed during two sessions of a nine-day urban combat training (UCT) course for cadets in the Swedish Armed Forces, one session employing leaded ammunition (leaded scenario) and one session employing unleaded ammunition (unleaded scenario). Blood lead levels (BLLs) were measured before and after the course for 42 cadets and five instructors. During the leaded scenario, the instructors' airborne exposure (geometric mean, GM, 72.0 μg/m³) was higher than that of cadets (GM 42.9 μg/m³). During the unleaded scenario, airborne concentrations were similar for instructors and cadets and considerably lower than during the leaded scenario (GM 2.9 μg/m³). Despite comparably low external lead exposures during the course, we saw a statistically significant increase in systemic exposure for cadets (BLL GM increased from 1.09 to 1.71 μg/dL, p < 0.001). For the five instructors, notable differences were seen depending on task. The largest increase was seen for the two instructors performing close supervision during the leaded scenario (BLL GM increased from 2.41 μg/dL to 4.83 μg/dL). For the remaining three instructors the BLLs were unchanged (BLL GMs were 1.25 μg/dL before the course and 1.26 μg/dL after). None of the participants exceeded the applicable biological exposure limits, but extrapolating our findings shows that instructors in the leaded scenario may reach levels around 10 μg/dL after a year of repeated exposures. We conclude that comparably low airborne concentrations can contribute to the body burden of lead and that additional measures to reduce exposure are warranted, particularly for instructors.

Reduction in lead exposures with lead-free ammunition in an advanced urban assault course

The training of soldiers for urban conflict involves marksmanship instruction on outdoor flat ranges and the teaching of close-quarter battle techniques in indoor facilities, referred to as shoot houses, where intense firing exercises can generate high air lead levels from small arms ammunition, flash bang grenades, and explosive devices. Levels of lead and copper in air were evaluated during five training activities of a 45-day training course using both stationary general area and breathing zone sampling over a 2-year period. Individual blood lead values were determined prior to and at course completion. Mean breathing zone lead concentrations for the five training activities ranged from 0.014 on the outdoor flat range to 0.064 mg/m³ inside shoot houses; with a change to lead-free ammunition the values were reduced to a range of 0.006-0.022 mg/m³. Isolated flash bang grenades generated very high general area lead concentrations (2.0 mg/m³), which in training were associated with the highest measured breathing zone concentration (0.16 mg/m³). For copper, mean breathing zone concentrations increased from 0.010 to 0.037 mg/m³ with the change to lead-free frangible ammunition on the outdoor range, but remained below the permissible exposure limit for copper fume. Inside shoot houses, mean breathing zone copper concentrations exceeded the permissible exposure limit with ball and lead-free frangible ammunition, ranging from 0.077-0.13 mg/m³. With the introduction of lead-free ammunition, when comparing the blood lead differences between start and finish of the course, there was a significant reduction in the mean blood lead difference from 13.3 µg/dL to 5.4 µg/dL. Options for mitigation of potentially high exposure areas using improved ventilation designs are discussed. These results advocate for improved designs for shoot house training facilities, stress the importance of removing lead from ammunition and explosive devices for training, and promote the continued need for implementation of controls to mitigate and manage metal exposures during training.