McKernan John L, Ellenbecker Michael J
National Institute for Occupational Safety and Health, Division of Surveillance Hazard Evaluation and Field Studies, Cincinnati, OH 45226, USA.
Ann Occup Hyg. 2007 Apr;51(3):269-79. doi: 10.1093/annhyg/mem006. Epub 2007 Mar 9.
Exothermic or heated processes create potentially unsafe work environments for an estimated 5-10 million American workers each year. Excessive heat and process contaminants have the potential to cause acute health effects such as heat stroke, and chronic effects such as manganism in welders. Although millions of workers are exposed to exothermic processes, insufficient attention has been given to continuously improving engineering technologies for these processes to provide effective and efficient control. Currently there is no specific occupational standard established by OSHA regarding exposure to heat from exothermic processes, therefore it is important to investigate techniques that can mitigate known and potential adverse occupational health effects. The current understanding of engineering controls for exothermic processes is primarily based on a book chapter written by W. C. L. Hemeon in 1955. Improvements in heat transfer and meteorological theory necessary to design improved process controls have occurred since this time. The research presented involved a review of the physical properties, heat transfer and meteorological theories governing buoyant air flow created by exothermic processes. These properties and theories were used to identify parameters and develop equations required for the determination of buoyant volumetric flow to assist in improving ventilation controls. Goals of this research were to develop and describe a new (i.e. proposed) flow equation, and compare it to currently accepted ones by Hemeon and the American Conference of Governmental Industrial Hygienists (ACGIH). Numerical assessments were conducted to compare solutions from the proposed equations for plume area, mean velocity and flow to those from the ACGIH and Hemeon. Parameters were varied for the dependent variables and solutions from the proposed, ACGIH, and Hemeon equations for plume area, mean velocity and flow were analyzed using a randomized complete block statistical design (ANOVA). Results indicate that the proposed plume mean velocity equation provides significantly greater means than either the ACGIH or Hemeon equations throughout the range of parameters investigated. The proposed equations for plume area and flow also provide significantly greater means than either the ACGIH or Hemeon equations at distances >1 m above exothermic processes. With an accurate solution for the total volumetric flow, ventilation engineers and practicing industrial hygienists are equipped with the necessary information to design and size hoods, as well as place them at an optimal distance from the source to provide adequate control of the rising plume. The equations developed will allow researchers and practitioners to determine the critical control parameters for exothermic processes, such as the exhaust flow necessary to improve efficacy and efficiency, while ensuring adequate worker protection.
放热或加热过程每年为约500万至1000万美国工人创造了潜在不安全的工作环境。过高的热量和工艺污染物有可能导致急性健康影响，如中暑，以及慢性影响，如焊工的锰中毒。尽管数百万工人接触放热过程，但对于不断改进这些过程的工程技术以提供有效和高效的控制，人们给予的关注不足。目前，美国职业安全与健康管理局（OSHA）尚未制定关于接触放热过程产生的热量的具体职业标准，因此，研究能够减轻已知和潜在不良职业健康影响的技术非常重要。目前对放热过程工程控制的理解主要基于W. C. L. 赫梅恩1955年撰写的一章内容。自那时以来，设计改进的过程控制所需的传热和气象理论已经有所改进。所开展的研究包括对放热过程产生的浮力气流所涉及的物理性质、传热和气象理论进行综述。这些性质和理论被用于确定参数并开发用于确定浮力体积流量所需的方程，以协助改进通风控制。本研究的目标是开发并描述一个新的（即提议的）流量方程，并将其与赫梅恩以及美国政府工业卫生学家会议（ACGIH）目前认可的方程进行比较。进行了数值评估，以比较提议方程得出的羽流面积、平均速度和流量的解与ACGIH和赫梅恩方程得出的解。对因变量的参数进行了变化，并使用随机完全区组统计设计（方差分析）分析了提议方程、ACGIH方程和赫梅恩方程得出的羽流面积、平均速度和流量的解。结果表明，在所研究的参数范围内，提议的羽流平均速度方程提供的平均值明显高于ACGIH方程或赫梅恩方程。在高于放热过程1米以上的距离处，提议的羽流面积和流量方程提供的平均值也明显高于ACGIH方程或赫梅恩方程。有了总容积流量的精确解，通风工程师和从业工业卫生学家就具备了设计通风罩及其尺寸以及将其放置在离源头最佳距离处以充分控制上升羽流所需的必要信息。所开发的方程将使研究人员和从业者能够确定放热过程的关键控制参数，例如提高效能和效率所需的排气流量，同时确保为工人提供充分保护。
