Potential consequences of nitric oxide release: An improved model informing worker safety

Both nitric oxide (NO) and nitrogen dioxide (NO₂) gasses are toxic to humans but are commonly found in industrial settings such as semiconductor manufacturing sites. Due to the spontaneous oxidation of NO to NO₂ under ambient conditions, individuals working with NO may in fact be exposed to both gasses in the case of an accidental release. Unfortunately, most safety materials provided to NO users do not address the potential for associated NO₂ toxicity, and, until now, models developed to predict health consequences following a release of NO have not appropriately considered the oxidation kinetics nor the toxicity of both NO and NO₂ in their assessments. This paper describes an improved multi-module model that addresses these limitations and explores whether facilities using NO should consider adopting measures that can mitigate the simultaneous health effects of both gasses. The model predicts the morbidity (intoxication/injury), mortality (death), and treatment outcomes that may arise following an industrial NO release by first calculating the doses of both NO and NO₂ received by exposed individuals and then applying newly defined toxicity parameters for NO and NO₂ to assign dose-dependent probabilities for the onset of intoxication and/or death and the ability of appropriate treatment(s) to save lives. Modeling results indicate low risk to worker health in the likeliest release scenarios while identifying less likely situations that carry substantially higher risk. Moreover, these results indicate that risks to worker health can be mitigated with simple measures like maintaining reliable alarms, adequate ventilation, and on-site supplies of methylene blue, as well as encouraging quick responses by personnel. With appropriate parameterization, the improved modeling framework is generalizable to any chemical release, especially multi-hazard releases resulting from the conversion of one toxic compound into another under likely environmental conditions. By directly addressing the toxicities of multiple compounds, the improved model presents a more realistic picture of the potential health consequences of a chemical release. This generalizable framework for modeling of multi-hazard chemical releases can inform preparedness and risk mitigation strategies for NO release events.