Hearing damage induced by blast exposure is a common injury in military personnel involved in most operation activities. Personal hearing protection devices such as earplugs come as a standard issue for Service members; however, it is not clear how to accurately evaluate the protection mechanisms of different hearing protection devices for blast overpressures (BOP). This paper reports a recent study on characterization of earplugs’ protective function to BOP using human cadaver ears and 3D finite element (FE) model of the human ear. The cadaver ear mounted with pressure sensors near the eardrum (P1) and inside the middle ear (P2) and with an earplug inserted was exposed to BOP in the blast test chamber. P1, P2, and BOP at the ear canal entrance (P0) were simultaneously recorded. The measured P0 waveform was then applied at the ear canal entrance in the FE model and the P1 and P2 pressures were derived from the model. Both experiments and FE modeling resulted in the P1 reduction which represents the effective protection function of the earplug. Different earplugs showed variations in pressure waveforms transmitted to the eardrum, which determine the protection level of earplugs.

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Introduction The peripheral auditory system and various structures within the central auditory system are vulnerable to blast injuries, and even blast overpressure is at relatively mild traumatic brain injury (TBI) level. However, the extent of hearing loss in relation to blast number and time course of post-blast is not well understood. This study reports the progressive hearing damage measured in chinchillas after multiple blast exposures at mild TBI levels (103–138 kPa or 15–20 psi). Materials and Methods Sixteen animals (two controls) were exposed to two blasts and three blasts, respectively, in two groups with both ears plugged with foam earplugs to prevent the eardrum from rupturing. Auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) were measured in pre- and post-blasts. Immunohistochemical study of chinchilla brains were performed at the end of experiment. Results Results show that the ABR threshold and DPOAE level shifts in 2-blast animals were recovered after 7 days. In 3-blast animals, the ABR and DPOAE shifts remained at 26 and 23 dB, respectively after 14 days. Variation of auditory cortex damage between 2-blast and 3-blast was also observed in immunofluorescence images. Conclusions This study demonstrates that the number of blasts causing mild TBI critically affects hearing damage.

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LV direct current (LVDC) distribution systems have recently been considered as an alternative approach to electrical distribution system infrastructure as they possess the flexibility and controllability that is required to facilitate the integration of low carbon technologies (LCT). For example, energising existing LV AC cables by DC with higher voltages (>0.4kV) can potentially release additional power capacity on LV cables and reduce the associated thermal losses. However, converting existing AC cables for DC operation may change the cable performance under faulted conditions, resulting in a change to its lifetime. The nature of future LVDC systems can be capacitive due to the characteristic of particular customers such as battery energy storage systems (BESS) and electric vehicles (EVs). A short-circuit fault on the DC side may lead to a discharge/release of significant transient energy in LV cables which was never anticipated under traditional LVAC networks. This paper quantifies the transient DC fault let-through energy which can be imposed on existing AC cables used for DC operation, and draws conclusions on the potential impact of such phenomena on the cable performance. A detailed model of an LVDC test network with three-core LV cables is developed using PSCAD/EMTDC for simulation studies.