The aim of the booth designer is to achieve laminar airflow at all relevant points in the paint booth. This can be accomplished by managing the airflow. Using a sheet metal shroud to manage the airflow is an effective means and is approved by NFPA-33. Laminar airflow does not necessarily mean the airflow is constant. In fact, if left at a constant level, the airstream has a tendency to degrade and develop vortices (room effects), which are damaging to the painter’s environment. A slight acceleration of air speed from front to back is helpful in controlling the vortices.
Room effects are hard to see and to understand. It is better to follow simple empirical practices to negate the effects of the room. Acceleration of the airflow is one such way to manage the problem. The other is by understanding booth pressure.
This negative/positive pressure discussion generally assumes that the paint booth is a place that is at a uniform pressure level. This is not true and the science of balancing paint booths, especially so-called “big rooms”, is easy to understand.