Determinants of SFE Toxicity: Interaction of Atmospheric, Dynamic, and Physiological Responses

The physical and chemical properties of an aerosol have a direct influence upon fire suppression mechanisms and extinguishing efficacy. These same properties are also basic determinants of aerosol inhalation toxicity. To evaluate the toxicity of an aerosol, it must first be determined if the aerosol can be inspired. Particles with a median aerodynamic diameter of 1-2 pm are capable ofpenetrating deep into the human tracheobronchial tree, reaching the alveolar acini. These acini are comprised of parenchymal tissues. which are highly susceptible to damage and least protected by clearance (defense) mechanisms. Both chemical and physical properties of inhaled particulate matter combine to control aerosol toxicity. The dose to regional lung tissue depends on particle size, particle specific surface area and chemical solubility. As is true of other routes of toxic entry into the body, tissue response to dissolved material in the lung is dependent on the chemical nature of the insult. Potential toxic effects include altered pulmonary function, irritation and altered gas exchange, leading to discomfort, altered oxygen uptake, incapacitation and death. In the case of pyrotechnically generated aerosols, carbon monoxide may also be present, resulting in increased carboxyhemoglobin levels and decreased oxygen uptake leading to disorientation and possible incapacitation. Aerosol toxic effects are not limited to the lung; dissolved material can be transported from the lung to other systems throughout the body. In addition to pulmonary and systemic effects, aerosolized material can cause irritation of the skin and/or nasal and ocular mucosa. The companion papers concerning SFE toxicity in this proceedings detail the observation of these effects for SFE exposures. This paper relates our observations to the basics of inhalation toxicology and aerosol science. Introduction The fire extinguishing engineering community has a significant interest in dry powder and mist fire extinguishing/suppression systems. As part of improving system efficacy, agent particle size is being reduced, bringing a significant fraction of the dispersed agent into the respirable range. Water mist systems and Encapsulated Micron Aerosol Agent (SFE) are two examples of such fire fighting systems. These systems must undergo toxicity evaluation and use permitting similar in scope to that used for gaseous extinguishing systems, requiring the effects of respirable particle toxicity be evaluated. The inhalation toxicity of aerosol agents is inherently more complex than a pure gas. However, this should not be a deterrent to their development or use. The purpose of this paper is to discuss the basic determinants of aerosol toxicity, illustrating them with the