Neutralization Kinetics and Transport Define the Dermal Decontamination Window for Warfare and Industrial Toxicants

Chemical warfare agents that are moderately to highly volatile can readily permeate the skin, posing an acute systemic toxicity risk. Effective decontamination depends on how intervention timing and chemical reactivity jointly shape dermal absorption, evaporation, and neutralization. While earlier finite-dose models characterized dermal uptake, they lacked decontaminant reactivity and failed to quantify how neutralization competes with diffusion and surface clearance. This work presents a unified, dimensionless framework integrating diffusion, evaporation, and reactive neutralization. The system behavior is governed by two dimensionless groups: a surface-loss number (π_surf) that captures combined evaporation and interfacial reaction and a Damköhler number (Da) that quantifies bulk neutralization relative to diffusion. Analytical solutions yield characteristic time constants describing the relative rates of absorption, surface clearance, and neutralization. Three distinct kinetic regimes emerge: (i) low Da (<3), where slow internal reaction leaves surface loss as the primary clearance mechanism; (ii) intermediate Da (3-8), characterized by competitive transport and reaction rates; and (iii) high Da (>8), where rapid bulk neutralization renders surface-based interventions progressively less effective. The framework identifies a critical decontamination window during which the applied decontaminant neutralizes the agent faster than it can enter the bloodstream, thereby minimizing systemic exposure. Implemented as open-source Python software, this tool can help emergency responders and regulatory agencies predict decontamination windows for chemical warfare agents and industrial toxicants.