Temperature influence on benzene behavior in crude oil during tank fires: Liquid-phase diffusion and implication for firefighter exposure

Hazardous material responders maintain conventional wisdom that elevated liquid temperature from a crude oil fire reduces volatility and therefore lowers the risk of exposure to volatiles in post-fire crude oil. After a crude oil tank fire is extinguished, responders often work near the post-fire crude oil when conducting damage assessments or removing oil from the tank’s structure. If the conventional wisdom is not true and the volatiles are not removed by heat, responders lacking adequate protection may be exposed to unhealthy airborne concentrations of toxic aromatic hydrocarbons such as benzene. Post-fire crude oil was examined quantitatively seeking answers regarding the survival of benzene and the risk posed to unprotected responders who are tasked with near-field engagement. The first study quantified hydrocarbon volatility of liquids in the heat-affected layer (hot zone) of crude oil following thirty-minute tank fire evolutions. Most notably, benzene persisted disproportionately to aromatic counterparts in post-fire crude oil. The second study utilized a novel-design tank fire apparatus that enabled temperature and aromatic liquid concentration analysis with emphasis on foam extinguishment as the variable. A relationship between benzene persistence and foam extinguishment was observed. The phenomena of benzene persistence in post-fire crude oil, with influence from foam extinguishment, initiated a hypothesis postulating the role of liquid-phase diffusion as a potential contributor. Hence, the third study which utilized a novel-design diffusion column to investigate the influence of an adjacent high temperature zone on benzene’s diffusivity. Benzene did not diffuse disproportionately to toluene, ethylbenzene or m-xylene, despite its higher diffusivity in solvents. Although the contributing variable to benzene persistence was not identified in this work, two significant findings contributed to the body of knowledge. First, post-fire crude oil should not be regarded as benign based on the observance of benzene and its persistence in crude oil following a tank fire. Secondly, liquid-phase diffusion can be disregarded for now as a contributor and further research should focus on alternate explanations. Ultimately, there is rebuttal to the belief that post-tank fire crude oil is benign, giving priority to benzene exposure in hazard communication for responders.