Numerous studies have shown that military and civil use of lead containing ammunitions is associated to severe environmental and health considerations i.e. high blood levels. This has led to the development of lead-free ammunition however these replacement products have been associated to other health implications such as respiratory irritation, asthma, fever and nausea. Emissions from shooting with small calibre ammunition makes up of a complex mixture of gases and particles. For instance, polycyclic aromatic hydrocarbons (PAHs) that are known to have mutagenic properties have been identified in emissions from small calibre rifles using nitro-based propellants (Moxnes et al, 2013). It has further been shown that respirable particles in the size range 0.29-0.57 μm from shooting were associated to higher mutagenic activity as compared to larger particle fractions (Palmer, 1994). The aim of this work was to develop a rapid method for quantitative chemical analysis of mutagenic and toxic organic compounds (PAHs and oxy-PAHs) associated to particles and to apply the method in a study of gunshot particles from lead free ammunition. Two standard reference materials, SRM1649b (urban dust) and SRM 1650b (diesel particulate matter) were used for method validation and comparison. In a 0.7 m 3 test chamber an assault rifle (AK5C) was mounted and three single shots of lead-free ammunition were fired through remote control. Particles were sampled on glassfiber filters (GFF, Ø25 mm) with a flow of 1.0 l/min for 15 minutes. Particles were also monitored with Electrical Low Pressure Impactor (ELPI) and a medium-volume particle sampler (pre-weighed PTFE-filters) to monitor dynamic properties and accurate mass concentrations, respectively.

Lead-free ammunition is becoming increasingly popular because of the environmental and human health issues associated with the use of leaded ammunition. However, there is a lack of data on the emissions produced by firing such ammunition. We report emission factors for toxic gases and particle-bound compounds produced by firing lead-free ammunition in a test chamber. Carbon monoxide, ammonia, and hydrogen cyanide levels within the chamber were analysed by Fourier transform infrared spectroscopy, while total suspended particles and respirable particles were determined gravimetrically. The metal content of the particulate emissions was determined and the associated organic compounds were characterized in detail using a method based on thermal desorption coupled to gas chromatography and mass spectrometry. The particulate matter (∼30 mg/round) consisted primarily of metals such as Cu, Zn, and Fe along with soot arising from incomplete combustion. Nitrogen-containing heterocyclic aromatic compounds such as carbazole, quinolone, and phenazine were responsible for some of the 25 most significant chromatographic peaks, together with PAHs, diphenylamine, and phthalates. Emission factors were determined for PAHs and oxygenated PAHs; the latter were less abundant in the gun smoke particles than in domestic dust and diesel combustion smoke. This may be due to the oxygen-deficient conditions that occur when the gun is fired. By using an electrical low pressure impactor, it was demonstrated that more than 90% of the particles produced immediately after firing the weapon had diameters of less than 30 nm, and so most of the gun smoke particles belonged to the nanoparticle regime.

STUDY DESIGN:A finite element (FE) model of the human neck was used to study the distribution of neck muscle loads during multidirectional impacts. The computed load distributions were compared to experimental electromyography (EMG) recordings.OBJECTIVE:To quantify passive muscle loads in nonactive cervical muscles during impacts of varying direction and energy, using a three-dimensional (3D) continuum FE muscle model.SUMMARY OF BACKGROUND DATA:Experimental and numerical studies have confirmed the importance of muscles in the impact response of the neck. Although EMG has been used to measure the relative activity levels in neck muscles during impact tests, this technique has not been able to measure all neck muscles and cannot directly quantify the force distribution between the muscles. A numerical model can give additional insight into muscle loading during impact.METHODS:An FE model with solid element musculature was used to simulate frontal, lateral, and rear-end vehicle impacts at 4 peak accelerations. The peak cross-sectional forces, internal energies, and effective strains were calculated for each muscle and impact configuration. The computed load distribution was compared with experimental EMG data.RESULTS:The load distribution in the cervical muscles varied with load direction. Peak sectional forces, internal energies, and strains increased in most muscles with increasing impact acceleration. The dominant muscles identified by the model for each direction were splenius capitis, levator scapulae, and sternocleidomastoid in lateral impacts, splenius capitis, and trapezoid in frontal impacts, and sternocleidomastoid, rectus capitis posterior minor, and hyoids in rear-end impacts. This corresponded with the most active muscles identified by EMG recordings, although within these muscles the distribution of forces and EMG levels were not the same.CONCLUSION:The passive muscle forces, strains, and energies computed using a continuum FE model of the cervical musculature distinguished between impact directions and peak accelerations, and on the basis of prior studies, isolated the most important muscles for each direction.

The numerical method of finite elements (FE) is a powerful tool for analysing stresses and strains in the human body. One area of increasing interest is the skeletal musculature. This study evaluated modelling of skeletal muscle tissue using a combination of passive non-linear, viscoelastic solid elements and active Hill-type truss elements, the super-positioned muscle finite element (SMFE). The performance of the combined materials and elements was evaluated for eccentric motions by simulating a tensile experiment from a published study on a stimulated rabbit muscle including three different strain rates. It was also evaluated for isometric and concentric contractions. The resulting stress-strain curves had the same overall pattern as the experiments, with the main limitation being sensitivity to the active force-length relation. It was concluded that the SMFE could model active and passive muscle tissue at constant rate elongations for strains below failure, as well as isometric and concentric contractions.

The hypothesis that muscle tension protects the spine from injuries in helicopter scenarios was tested using a finite-element model of the human head and neck. It was compared with cadaver crash sled experiment with good correlation. Then, simulations were performed with a sinusoidal velocity (5-22 G) applied at T1 60 to the horizontal plane. The model with relaxed muscle activation had delayed and decreased peak head rotation compared with passive properties only. Full muscle activation decreased the injury risk for the 13.5-22 G impacts. A sensitivity study of the impact angle showed a very slight variation of the resulting neck flexion, and 1 change affected all ligament injury predictions less than 4%. Finally, simulations with helmets resulted in increased ligament and disc strains with increasing helmet mass and with an anterior or inferior shift of the centre of gravity. It is concluded that the hypothesis seems to hold.

Study Design. A finite element (FE) model of the human neck with incorporated continuum or discrete muscles was used to simulate experimental impacts in rear, frontal, and lateral directions.Objective. The aim of this study was to determine how a continuum muscle model influences the impact behavior of a FE human neck model compared with a discrete muscle model.Summary of Background Data. Most FE neck models used for impact analysis today include a spring element musculature and are limited to discrete geometries and nodal output results. A solid-element muscle model was thought to improve the behavior of the model by adding properties such as tissue inertia and compressive stiffness and by improving the geometry. It would also predict the strain distribution within the continuum elements.Methods. A passive continuum muscle model with nonlinear viscoelastic materials was incorporated into the KTH neck model together with active spring muscles and used in impact simulations. The resulting head and vertebral kinematics was compared with the results from a discrete muscle model as well as volunteer corridors. The muscle strain prediction was compared between the 2 muscle models.Results. The head and vertebral kinematics were within the volunteer corridors for both models when activated. The continuum model behaved more stiffly than the discrete model and needed less active force to fit the experimental results. The largest difference was seen in the rear impact. The strain predicted by the continuum model was lower than for the discrete model.Conclusion. The continuum muscle model stiffened the response of the KTH neck model compared with a discrete model, and the strain prediction in the muscles was improved.

The Finite Element method is a powerful tool for analyzing the biomechanics of the human body. One area that has attracted increasing attention is the cervical musculature and its influence in neck injury mechanisms. Most cervical FE models of today use spring-elements as muscles and are limited to discrete geometries and nodal output results. A solid-element muscle model however, will improve the geometry and add properties such as tissue inertia and compressive stiffness. It also enables analysis of element stresses and strains within the muscular tissue. The aim of this study was to determine how a continuum muscle model influences the impact behavior of a human neck FE model compared to a discrete muscle model. The 3D geometries of the neck muscles were digitized from MR images of 50 percentile males and positioned relative to the KTH FE neck model in line with anatomical data from the literature. The muscles were modeled using solid finite elements and a non-linear, viscoelastic continuum material model. The behavior of the new muscle model during impact was compared to an existing discrete muscle model for frontal, rear-end, lateral and oblique impacts. The continuum muscle model stiffened the response of the KTH neck model and improved the boundary conditions for the vertebral column compared to a discrete model.

Increasingly complex models of the neck neuromusculature need detailed muscle and kinematic data for proper validation. The goal of this study was to measure the electromyographic activity of superficial and deep neck muscles during tasks involving isometric, voluntary, and reflexively evoked contractions of the neck muscles. Three male subjects (28-41 years) had electromyographic (EMG) fine wires inserted into the left sternocleidomastoid, levator scapulae, trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus muscles. Surface electrodes were placed over the left sternohyoid muscle. Subjects then performed: (i) maximal voluntary contractions (MVCs) in the eight directions (45 deg intervals) from the neutral posture; (ii) 50 N isometric contractions with a slow sweep of the force direction through 720 deg; (iii) voluntary oscillatory head movements in flexion and extension; and (iv) initially relaxed reflex muscle activations to a forward acceleration while seated on a sled. Isometric contractions were performed against an overhead load cell and movement dynamics were measured using six-axis accelerometry on the head and torso. In all three subjects, the two anterior neck muscles had similar preferred activation directions and acted synergistically in both dynamic tasks. With the exception of splenius capitis, the posterior and posterolateral neck muscles also showed consistent activation directions and acted synergistically during the voluntary motions, but not during the sled perturbations. These findings suggest that the common numerical-modeling assumption that all anterior muscles act synergistically as flexors is reasonable, but that the related assumption that all posterior muscles act synergistically as extensors is not. Despite the small number of subjects, the data presented here can be used to inform and validate a neck model at three levels of increasing neuromuscular-kinematic complexity: muscles generating forces with no movement, muscles generating forces and causing movement, and muscles generating forces in response to induced movement. These increasingly complex data sets will allow researchers to incrementally tune their neck models' muscle geometry, physiology, and feedforward/feedback neuromechanics.

Finite element analysis of the effects of head-supported mass on neck responses : Complete phase two report, United states army european research office of the U.S. army