A model was developed to describe the emission of phosphine gas from the interior of a tobacco warehouse to the outside during controlled aeration after fumigation of the warehouse. We used a fan/stack exhaust system to control the aeration, but other systems can be used. Model inputs include phosphine concentrations in the warehouse just prior to aeration, warehouse characteristics, and characteristics of the system used to release phosphine. Model outputs for any time during aeration include the emission rate of phosphine from the warehouse, the phosphine concentration remaining in the warehouse, and suggested exhaust rates that help fumigators comply with regulatory standards on phosphine emission rates. (Exhaust rate refers to release of air/phosphine mixture from the warehouse [=volume/time], but phosphine emission rate refers to the amount of phosphine [=mass/time]). The model also calculates how much exhaust rates can be increased at regular time intervals to hasten aeration without exceeding the initial phosphine emission rate. The model can be used by fumigators to comply with regulatory standards on phosphine emissions, and by regulators to assess that compliance. Diffusion of phosphine from the packaged tobacco (cases) into the freespace of the warehouse and its impact on the model are discussed.

Author notes

2 Flue-Cured Tobacco Cooperative Stabilization Corporation, Raleigh, NC 27605-12300.