Presence-gated VOC sensing for urban search and rescue applications.

Urban search and rescue (USAR) operations require sensing modalities that remain effective under conditions where visibility-dependent techniques are degraded by dust, smoke, debris, or occlusion. This work presents a presence-gated volatile organic compound (VOC) sensing approach intended to support triage decisions in USAR scenarios. The system combines an actively sampled metal-oxide gas sensor array with environmental compensation and embedded inference, while a 24 GHz FMCW radar is used to verify human presence through micro-motion cues and suppress chemistry-only false alarms. The sensing pipeline is designed for microcontroller-class execution, employing deterministic timing, duty-cycled operation, and compact feature extraction suitable for resource-constrained platforms. Offline evaluation was conducted using tethered data collection to assess instrument-level separability across controlled exposure conditions, including fresh air, surrogate injury-related VOC mixtures, and reference gases. Results are reported in terms of confusion matrices, ROC and precision-recall curves, and feature-importance analysis, emphasizing system behavior and feasibility rather than diagnostic performance. The findings demonstrate that presence-gated VOC sensing can provide a complementary information channel for USAR applications, while large-scale field validation and biological specificity remain topics for future investigation.