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，该设施可能已经设计并安装了内部通风系统。他们可能有一个维护部门，该部门是针对制造罩和跑到排气扇的管道。在其他情况下，他们可能已签订公司安装aventilation system. 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.
Incorrect Hood Usage
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
另一个常见的缺陷是污染源的捕获速度不足。可移动的提取臂，插槽罩和其他引擎盖类型必须定位足够接近，以获得足够的捕获速度，以有效地从员工的呼吸区中取出污染物。通常，引擎盖的位置是问题，引擎盖可以重新定位到生成点。在某些情况下，必须增加通风以达到所需的捕获速度。
Improper Ductwork Sizing
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.
- Determining exhaust flow rates and capture velocities required.
- 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.