Efficient and Reliable Assessment of the Maximum Local Tissue Temperature Increase at the Electrodes of Medical Implants under MRI Exposure.

Standard risk evaluations posed by medical implants during magnetic resonance imaging (MRI) includes (i) the assessment of the total local electromagnetic (EM) power (P) absorbed in the vicinity of the electrodes and (ii) the translation of P into a local in vivo tissue temperature increase ∆T (P2∆T) in animal experiments or simulations. We investigated the implant/tissue modeling requirements and associated uncertainties by applying full-wave EM and linear bioheat solvers to different implant models, incident field conditions, electrode configurations, and tissue models. Results show that the magnitude of the power is predominately determined by the lead, while the power distribution, and the P2∆T conversion, is determined by the electrode and surrounding tissues. P2∆T is strongly dependent on the size of the electrode, tissue type in contact with the electrode, and tissue inhomogeneity (factor of >2 each) but less on the modeling of the lead (<±10%) and incident field distribution along the lead (<±20%). This was confirmed by means of full-wave simulations performed with detailed high-resolution anatomical phantoms exposed to two commonly used MRI clinical scenarios (64 and 128 MHz), resulting in differences of less than 6%. For the determination of P2∆T, only the electrode and surrounding tissues must be modeled in great detail, whereas the lead can be modeled as a computationally efficient simplified structure exposed to a uniform field. The separate assessments of lead and electrode reduce the overall computational effort by several orders of magnitude. The errors introduced by this simplification can be considered by uncertainty terms. Bioelectromagnetics. 2019;40:422-433. © 2019 Bioelectromagnetics Society.

Comment on Redmayne, M.; Maisch, D.R. ICNIRP Guidelines' Exposure Assessment Method for 5G Millimetre Wave Radiation May Trigger Adverse Effects. Int. J. Environ. Res. Public Health 2023, 20, 5267.

This article discusses the contention in the commented-upon paper that Brillouin precursors generated by 5G New Radio (5G NR) and other cellular systems are a possible cause of tissue damage at deeper layers of tissue than the power penetration depth of the carrier frequency. The original theory for Brillouin precursors from pulsed radiofrequency signals (RF-EMF) and speculation about their possible health effects dates back to the 1990's and was based on studies of the propagation of very short (nanosecond) ultrawide-bandwidth RF pulses through water. This assumption is not correct for cellular telephone signals due to their narrow bandwidth. The commented-on paper provides no alternative rationale as to why Brillouin effects should cause tissue damage from RF-EMF radiation from cellular and other communications systems. Other inaccuracies in this paper concerning thermal responses of tissue to RF-EMF are also noted.

Investigation of the dual performance of thermal protective clothing with deformation under low radiant heat exposure.

Occupational workers in thermal exposure have frequent physical activities that may lead to fabric deformation of thermal protective clothing. To deeply understand the impact of fabric deformation on its dual thermal protective and thermal hazardous performance, a modified experimental instrument was used to simulate different extents of fabric tensile deformation and compression deformation. The results demonstrated that increasing tensile ratios during exposure decreased heat storage within a fabric system, but increased the skin absorbed energy. Tensile ratios had a more negative impact on the thermal protective performance of a single-layer fabric than of a double-layer fabric system. Increasing tensile ratios during cooling decreased heat discharge to the skin, but the applied compression significantly improved the heat discharge. In addition, regression models were established to examine the effect of fabric deformation and demonstrated that the thermal hazardous performance of fabrics was more affected by compression than by tensile deformation.

Estimation of thermal hazards in surrounding rock of subway tunnel under dual periodic temperature boundaries: a case study.

Thermal hazards of the surrounding rock of subway tunnels are becoming apparent, in which the heat transfer in the surrounding rock plays a crucial role. Due to the shallow buried depth, the subway tunnel encounters a more complicated heat exchange under the duplicate effects of periodic temperature fluctuation of ground atmosphere and periodic temperature variation of tunnel wind, but this issue has not been fully addressed. In this work, a transient heat transfer model of tunnel surrounding rock based on dual periodic temperature boundaries was established. A solver was developed to estimate the temperature rise and heat transfer of surrounding rock. The correctness of this model was then verified by comparing with previous empirical values and semi-empirical equations. The results show that the temperatures of the surrounding rock at different depths still fluctuate following the simple harmonic waves, and there are some regions that are heavily affected by the duplicate effects, such as the overlying strata of the tunnel. The surrounding rock generally exhibits heat storage in annual cycle, but the total heat storage decreases year by year until it tends to stabilize. Furthermore, the shallower the tunnel is buried, the greater the influence of ground temperature and the higher the temperature rise in the tunnel surrounding rock. This research provides an alternative approach to determine the heat storage of tunnel surrounding rock and evaluates the process of thermal disaster manifestation of subway.

A comprehensive investigation on the thermal and toxic hazards of large format lithium-ion batteries with LiFePO4 cathode.

Toxic gases released from lithium-ion battery (LIB) fires pose a very large threat to human health, yet they are poorly studied, and the knowledge of LIB fire toxicity is limited. In this paper, the thermal and toxic hazards resulting from the thermally-induced failure of a 68 Ah pouch LIB are systematically investigated by means of the Fourier transform infrared spectroscopy (FTIR) and 1/2 ISO full scale test room. The LIBs with higher state of charge (SOC) are found to have greater fire risks in terms of their burning behavior, normalized heat release rate, and fire radiation, as well as the concentration of toxic gases. Specifically, the thermal hazards are evaluated by combining the effects of convective and radiative heat. The major toxic gases detected from the online analysis are CO, HF, SO2, NO2, NO and HCl. Furthermore, Fractional Effective Dose (FED) and Fractional Effective Concentration (FEC) models are used to quantitatively assess the overall gas toxicity. Results show that the effects of irritant gases are much more significant than those of asphyxiant gases. HF and SO2 have much greater toxicity than the other fire gases. The maximum FEC value is approaching the critical threshold in such fire scenarios.

Investigation of the thermal hazardous effect of protective clothing caused by stored energy discharge.

In addition to direct thermal energy from a heating source, a large amount of thermal energy stored in clothing will continuously discharge to skin after exposure. Investigating the thermal hazardous effect of clothing caused by stored energy discharge is crucial for the reliability of thermal protective clothing. In this study several indices were proposed and applied to evaluate the impact of thermal energy discharge on human skin. The heat discharge from different layers of fabric systems was investigated, and the influences of air gaps and applied compression were examined. Heat fluxes at the boundaries of fabric layers and the distribution of heat discharge were determined. Additionally, the correlation between heat storage during exposure and heat discharge after exposure was identified. The results demonstrated that heat discharge to the skin could be correlated with heat storage within the fabric, however, it highly depended on the air gap under clothing, the applied compression, and the insulation provided by the fabric layers. Results from this study could contribute to thoroughly understanding the thermal hazardous effect of clothing and enhance the technical basis for developing new fabric combinations to minimize energy discharge after exposure.

The influence of manganese-cobalt oxide/graphene on reducing fire hazards of poly(butylene terephthalate).

By means of direct nucleation and growth on the surface of graphene and element doping of cobalt oxide (Co3O4) nano-particles, manganese-cobalt oxide/graphene hybrids (MnCo2O4-GNS) were synthesized to reduce fire hazards of poly(butylene terephthalate) (PBT). The structure, elemental composition and morphology of the obtained hybrids were surveyed by X-ray diffraction, X-ray photoelectron spectrometer and transmission electron microscopy, respectively. Thermogravimetric analysis was applied to simulate and study the influence of MnCo2O4-GNS hybrids on thermal degradation of PBT during combustion. The fire hazards of PBT and its composites were assessed by the cone calorimeter. The cone test results had showed that peak HRR and SPR values of MnCo2O4-GNS/PBT composites were lower than that of pure PBT and Co3O4-GNS/PBT composites. Furthermore, the incorporation of MnCo2O4-GNS hybrids gave rise to apparent decrease of pyrolysis products containing aromatic compounds, carbonyl compounds, carbon monoxide and carbon dioxide, attributed to combined impact of physical barrier for graphene and cat O4 for organic volatiles and carbon monoxide.