Why do I need to implement a time delay before opening the cabinet doors? Surely if the extraction is fit for purpose this shouldn’t be necessary?

The extraction unit will always take a period of time to clear the cabinet, no matter what the air flow is. You can introduce more air changes to reduce the delay time, however there is a limit. Over extraction creates its own set of issues which can include poor filter life and filter bypass which can be costly and inefficient.

Accurate clearance times will vary depending on the application and can be established using a smoke test.