Safety Analysis of Coupled Electromagnetic Wave Energy in Underground Coal Mine Energy Storage Type Metal Structures

Under specific conditions, metallic structures in coal mine tunnels can couple with electromagnetic waves emitted by Radio Frequency (RF) equipment, potentially generating spark discharges. The GB/T 3836.1-2021 Standard (Explosive Atmospheres-Part 1: Equipment General Requirements) restricts RF equipment output power to $\leqslant 6 ~\mathrm{W}$. However, this stringent threshold significantly constrains the deployment of $\text{5 G}$ communication systems and wireless power transfer technologies in mining. Current research overlooks the potential for temporal energy accumulation of coupled electromagnetic waves in metallic structures. In this study, we present an analytical method to characterize coupled electromagnetic wave energy in energy-storing metallic structures. Mathematical derivations of spark discharge energy were derived by establishing: (i) a model of electromagnetic wave propagation in mine tunnels, and (ii) an equivalent circuit for energy-storing metallic structures. Using MATLAB simulations, we analyzed parameters influencing spark discharge energy, revealing that:(1) Spark discharge energy decreases rapidly with increasing electromagnetic wave frequency (stabilizing at $\geqslant 200 \text{MHz}$) and declines with larger antenna angular parameters (within $0^{\circ}-45^{\circ}$); (2) Spark discharge energy increases with RF equipment output power but decreases with greater equivalent distance. Beyond a critical distance, output power ceases to be the dominant factor, necessitating safety thresholds calibrated to transmitter-receiver distance; (3) At minimum safety distances, RF equipment output power $\leqslant 20.9 ~\mathrm{W}$ remains intrinsically safe. These conclusions provide a theoretical foundation and simulation framework for revising RF power threshold regulations in GB/T 3836.1.