Airborne metal nanoparticles released by azides detonation: determination and potential public exposure

Abstract

Metal azides are highly energetic materials that release a large amount of gas upon detonation. They also release metal particles, generating an aerosol. The most common azide is sodium azide (NaN₃), which is used nowadays in car airbags. If the decomposition is not complete, harmful azide particles might be inhaled. Heavy metal azides find application as a primary explosive (primer) in ammunition. Public health officials have raised concerns about heavy metal particles released during training in shooting ranges. We identify a lack of knowledge on airborne metal particles properties released from azide detonation and on the analytical methods applied to characterize them. As a case study, we detonated milligram amounts of silver azide, copper azide, and a mixture of them in a glove box. We then analyse the airborne particles with an ensemble analytical setup, able to measure real-time their particle size distribution and chemical composition. We detected spherical metal nanoparticles in the range of 2-500 nm. These findings and the developed analytical tools may allow identifying airborne nanoparticles the passenger compartments of vehicles after airbag activation as well as in indoor shooting ranges, contributing to the evaluation of public health risks.

Figure 1

AgNPs (a) and CuNPs (b) after azides detonation directly collected on the TEM grid in the outlet gas stream from the glove box without particle size selection.

Figure 2

Schematic representation of the experimental setup for time-resolved characterization of single nanoparticles generated by metal azides detonation. DMA differential mobility analyzer; RDD rotating disk diluter; MFC mass flow controller; spICP-MS inductively coupled plasma mass spectrometry working in single particle mode.

Figure 3

The time-resolved particle size distribution of AgNPs (top) and CuNPs (bottom) after the detonation of AgN₃ and CuN₆, respectively, in the glove box, detected by spICP-MS after DMA selection at 50, 80, 100, 150, 200, 250, and 300 nm.

Figure 4

Reconstruction of the time-resolved Ag (a, b) and Cu (c, d) particle number population after the detonation of AgN₃ and CuN₆, respectively.

Figure 5

HAADF STEM images of NPs collected offline after the explosion of AgN₃ and CuN₆ mixture in the glove box (a) and STEM-EDX at the Ag L-edge (b), Cu K-edge (c), and overlay of Ag L-edge and Cu K-edge (d) respectively.

Figure 6

HAADF Images of NPs collected offline after the explosion of AgN₃ and CuN₆ mixture in the glove box (a) and STEM-EDX at the Ag L-edge (b), Cu K-edge (c) and overlay of Ag L-edge and Cu K-edge (d) after phase annealing induced under TEM beam exposure.

Figure 7

The time-resolved mass equivalent particle size distribution of Ag (top) and Cu (bottom) after the detonation of AgN₃ and CuN₆ mixed samples in the glove box characterized by spICP-MS after the selection of DMA at 50, 80, 100, 150, 200, 250, and 300 nm.

Figure 8

The time-resolved particle number concentration of Ag (a, b) and Cu (c, d) after the detonation of AgN₃ and CuN₆ mixed samples in the glove box at each DMA-selected size.

Figure 9

(A) Detail of the coaxial cable section used to ignite the azide material. The visible spark (double) is generated with a piezo crystal. In the micrograph, the azide pellet is not placed in order to show the working principle and the generated spark (double). (B) Schematic representation of the ignition system. A standard coaxial cable is used as support for the azide pellet. Kapton tape is used to keep the pellet in place, fixed with a teflon ring.