Keil Charles B, Nicas Mark
Environmental Health Program, College of Health and Human Services, Bowling Green State University, Bowling Green, OH 43043, USA.
AIHA J (Fairfax, Va). 2003 Jul-Aug;64(4):445-54. doi: 10.1202/341.1.
Relatively small spills of volatile liquids can result in short-term, high-concentration exposures. Because of the transient nature of these exposures, air sampling may be precluded. As an alternative, exposure assessment can be done by mathematical modeling. The vapor emission rate from small spills is highest immediately following the spill and decreases as the surface area available for mass transfer decreases and evaporation cools the liquid. This decreasing emission rate is not described by any of the existing evaporation rate models. The authors present an evaporation rate model that describes the changing emissions as exponentially decreasing. The rate of decrease is governed by an evaporation rate parameter alpha, which has the unit of min(-1) and can be estimated based on experimental measurements. The authors measured alpha for a suite of compounds and different sizes of spill. They found that alpha can be estimated for hydrocarbons containing only C, H, and O with the equation: alpha=0.000524 VP + 0.0108 SA/Vol, where VP is the vapor pressure of the liquid and SA/Vol is the surface area to volume ratio. Next, the authors integrated the exponentially decreasing emission rate into a well-mixed room versus a near field/far field dispersion construct to predict vapor concentrations. A preliminary experiment was conducted in a test room to compare measured concentrations with the concentrations predicted by the models. The well-mixed room model performed well based on ANSI indoor air model evaluation criteria. The predicted near field concentrations showed a poor fit to the measured values based on the ANSI criteria, although overall they did capture the observed time profile.
挥发性液体的相对小泄漏可能导致短期的高浓度暴露。由于这些暴露的短暂性，空气采样可能无法进行。作为替代方案，可以通过数学建模进行暴露评估。小泄漏后的蒸汽排放率在泄漏后立即最高，并随着可用于传质的表面积减小以及蒸发使液体冷却而降低。现有的任何蒸发率模型都没有描述这种不断降低的排放率。作者提出了一个蒸发率模型，该模型将不断变化的排放描述为指数下降。下降速率由蒸发率参数α控制，其单位为min(-1)，可以根据实验测量进行估算。作者测量了一组化合物和不同泄漏尺寸的α。他们发现，对于仅含有C、H和O的碳氢化合物，可以用以下方程估算α：α = 0.000524VP + 0.0108SA/Vol，其中VP是液体的蒸气压，SA/Vol是表面积与体积之比。接下来，作者将指数下降的排放率整合到一个充分混合的房间模型与近场/远场扩散模型中，以预测蒸汽浓度。在一个测试房间进行了初步实验，以比较测量浓度与模型预测的浓度。根据美国国家标准学会（ANSI）室内空气模型评估标准，充分混合的房间模型表现良好。基于ANSI标准，预测的近场浓度与测量值拟合不佳，尽管总体上它们确实捕捉到了观察到的时间分布。
