Background The High-altitude Nuclear Electromagnetic Pulse (HEMP) poses a significant threat to electronic and electrical systems. The evolving complexity of electromagnetic environments demands more accurate characterization of HEMP^,s early-time (E₁), intermediate-time (E₂), and late-time (E₃) phases for reliable impact assessment. The recent publication of IEC 61000-2-9:2025 introduces key updates to the 1996 edition, necessitating a systematic comparative analysis.

Purpose This study aims to conduct a comprehensive comparison between the IEC 61000-2-9:1996 and 2025 standards. The goal is to elucidate the technical evolution in describing HEMP^,s electric and magnetic field waveforms, amplitude spectra, and energy fluence spectra, thereby clarifying the new standard's enhancements in accuracy and real-world alignment.

Methods A detailed comparative analysis is performed, focusing on the time-domain waveforms, amplitude spectra, and energy fluence spectra for both electric and magnetic fields across the E₁, E₂, and E₃ phases. Key updates in the 2025 edition are examined, including new analytic expressions, revised waveform formulas incorporating ground conductivity, supplementary magnetic field descriptions, and changes in spectral definitions.

Results Significant updates in the 2025 edition are identified. For the E₁ electric field, an exponential-rational (QEXP) analytical expression is introduced alongside the classic double-exponential (DEXP) form, with new information on ground surface variation features and revised understanding of the far-field region. The E₃ electric field waveform formula is modified from a fixed-conductivity expression, E₃(t), to a conductivity-dependent one, E₃(σ_g, t). The description of the E₁ magnetic field is supplemented, and the late-time magnetic field component is newly introduced. While the E₂ amplitude spectrum remains unchanged, those of E₁ and E₃ are revised. Furthermore, the frequency threshold for defining the far-field power spectrum is raised to f > 10⁷ Hz.

Conclusions The IEC 61000-2-9:2025 standard provides a more accurate and practically relevant description of the HEMP environment compared to its 1996 predecessor. These updates provide an improved theoretical basis and enhanced guidance for evaluating the impact of HEMP on various systems and designing effective protective measures, which is crucial for addressing electromagnetic safety challenges in critical infrastructure.