A model for the spontaneous removal of airborne hydrogen chloride by common surfaces

Abstract The toxicity of hydrogen chloride, HCl, released from the decomposition of poly(vinyl chloride) in fires, has received considerable attention. In the most widely accepted single-or multi-compartment fire models appearing in the literature, HCl is treated as a conserved species during transport from the point of origin, along with the other products of combustion. It is demonstrated here that significant amounts of HCl readily adsorb on and then react with and/or diffuse into many types of common interior surfaces. Modeling the removal process of HCl from the gas in contact with such surfaces is the subject of this paper. The model is intentionally formulated so that it can be incorporated into general fire models. Five common surfaces are studied. Each is modeled in terms of five parameters describing the surface equilibrium concentration of HCl and the rate of disapperance from the surface of the adsorbed HCl. Mass transfer coefficients for HCl are variously predicted or fitted for the non-standard types of flow considered, many of which are gravity-driven. A criterion is derived from the model to predict when mass transfer will be rate-limiting. This criterion indicates that, in the majority of practical cases, mass transfer is not rate-limiting, thus permitting the use of rough estimates of the mass transfer coefficient to obtain satisfactory results. The model is verified with experimental data from a variety of scenarios.

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