How do plain hood openings differ from flanged hood openings?

Plain hood openings are characterized by their lack of a flange, which is a protruding edge or border that can be found in flanged openings. The absence of a flange in plain openings means that they are simply designed to allow air to enter without any structural enhancement that would direct or facilitate airflow. This design can lead to limitations in how effectively these openings capture airborne contaminants, as the capture efficiency is often improved with features that help streamline the airflow into the hood.

In contrast, flanged openings are specifically designed to enhance the efficiency of airflow and capture by incorporating a flange that helps direct air into the hood more effectively. Flanges can also aid in creating a better seal to ensure that the air being drawn in is more effectively contained, which helps in processes like fume extraction.

Thus, the distinction between plain and flanged openings is primarily related to the presence or absence of the flange, which has implications for their functionality in capturing air and contaminants.