This work presents a phenomenological extension of a previously proposed conductive-surface quantum decoherence framework toward electromagnetic shielding phenomena. The study investigates whether conductivity-induced decoherence may provide an additional contribution to electromagnetic shielding effectiveness by suppressing coherent electromagnetic wave propagation.A modified shielding formulation incorporating a decoherence-dependent attenuation term is developed and analyzed under asymptotic boundary conditions. Literature-based numerical evaluations using conductive composite shielding data are further utilized to examine possible correlations between environmental coupling strength and total shielding effectiveness.The framework preserves the classical electromagnetic shielding limits under negligible decoherence conditions while proposing an additional quantum-scale attenuation contribution under stronger decoherence regimes. The present model is intended as a theoretical and phenomenological interpretation rather than a complete microscopic quantum electrodynamic derivation.Keywords: electromagnetic shielding, quantum decoherence, open quantum systems, conductive materials, EMI shielding, Lindblad dynamics, phenomenological modeling.