When performing industrial hygiene exposure assessments, one of the key things we evaluate is if adequate engineering controls are in place to lower worker exposure. Although a facility may have chemical fume hoods installed, employee exposure can still be elevated. A consultant then has the difficult task of telling a client that the local exhaust ventilation system that they invested in is not effective in reducing their employee exposures.

在某些情况下，设施可能在内部设计并安装了通风系统。他们可能有一个维护部门，负责制造引擎盖和运行排气扇的管道系统。在其他情况下，他们可能与一家公司签订了安装通风系统. In both examples, time and money were invested to reduce worker exposure to chemical vapors, particulates, or fumes. This blog will address a few common pitfalls when trying to design an industrial ventilation system.

发动机罩使用不当

通常,当员工的风险敞口are elevated and ventilation is provided, the type of hood installed is incorrect for reducing employee exposure to a contaminant. For example, a facility may install a canopy hood over a dip tank and although this design may be effective for maintaining vapor concentrations of a flammable liquid below 25% of the lower flammability limit (LFL), the hood may not prevent exposure to employees who operate the tank. This is because the employee may be standing in the pathway of the contaminant when it is being pulled away from the surface of the dip tank and up to the canopy hood. In situations like this, a slot hood — positioned behind the tank instead of above it — is the better option for controlling exposures. There are recommended guidelines and standard industry practices regarding the types of exhaust ventilation that will work best for various types of exposure sources.

捕获速度不足

另一个常见的陷阱是污染物源的捕获速度不足。可移动的抽气臂、槽式抽气罩和其他类型的抽气罩必须放置在离产生点足够近的位置，以便有足够的捕集速度，有效地将污染物从员工的呼吸区清除。通常，发动机罩的位置是个问题，可以将发动机罩重新定位到更靠近生成点的位置。在某些情况下，必须增加通风以达到所需的捕获速度。

管道系统尺寸不当

The last pitfall we will discuss is ductwork. Ductwork with a diameter that is too narrow and/or elongated will not provide the air flow needed to capture the contaminant.

At Braun Intertec we can assist with assessing ventilation performance, including the following:

• Performing ventilation performance verification testing of newly installed equipment.
• Performing routine ventilation measurements of existing equipment.
• 确定所需的排气流量和捕获速度。
• Determining the correct type of local exhaust capture system needed and flow rates required.

If you would like to speak with someone in more detail about industrial exhaust ventilation design and/or assessment, please give us a call or click the link below to fill out our Contact Us form.