Solution for sudden contamination transport through air duct system: Under a puff release

When a chemical or biological agent is suddenly released into ventilation ducts, agent concentration along the whole ductwork should be promptly and accurately determined. In this work, an advection-diffusion model was suggested to calculate the agent transport in the air ducts. A node model was constructed for the agent dispersion at the duct junctions. Under a puff injection of the agent in the ductwork, the two models were integrated to derive the theoretical solution for the concentration dynamics. An experiment, using DEHS (diethylhexyl sebacate) aerosols as the representative agent pollution, was conducted to present the concentration dynamics within an air ductwork. Well agreement was observed between the theoretical predictions and the experimental results even with the extremely large sectional area. In this study, time characteristics were further defined and discussed to investigate the continuous normal distribution pattern of agent concentration along the flow direction in the ductwork. Such discussion helped to determine the exact time when the agent arrived at and traveled through a certain location after a puff release. It was also used to obtain the potential exposure at the outlets of the ductwork. The present work was expected to assist the early-warning and source identification of a potential chemical or biological agent attack in the ventilation ductwork.