Root Blower

One possibility would be to sustain a viable atmosphere in which people are intended to work.

This is most likely for proper ventilation for workers in the area, especially if it is a confined space. If they are continuously run, then there may be another reason. These are commonly used during boiler repairs during outages.

Iron and steel rusts. This soaks up atmospheric oxygen. If you have to clean inside any iron/steel vessel and there is any rust, never go inside until the space has been ventilated.

Please provide a sketch of the area and the installation you are talking about. All depends on what exactly it looks like and your question can be interpreted differently.

the pit is for blowdown? How big? how the pipes are routed? How the pit is drained and used....

Boiler feed water is normally "oxygen" hungary water after de-oxygenator. What ever is drained from the boiler will also be like that. To make water usable after drain or to drain it to earth or some river etc., it is being aerated by injecting air at the bottom of the drain pit.