Safety Knights

Ventilation requirements are based on the potential for a hazardous atmosphere, whether that be oxygen-deficiency, oxygen-enrichment, or a build-up of contaminants - not based on a certain depth or configuration of the space.

Requiring ventilation in all pits is not required unless there is a potential for a hazardous atmosphere, but it's still a good best practice as long as the ventilation doesn't create a hazard in itself. If there are flammable atmospheres, make sure your ventilation fan is grounded and bonded to prevent static buildup and a potential ignition source.

Below is an excerpt from NFPA 350 regarding this topic.

"The number of required air changes should be determined by testing and evaluating the atmosphere within the confined space. It is essential to consistently and reliably maintain an acceptable oxygen level and concentrations of contaminants in the breathing zone of Entrants are at or below the recognized occupational exposure limits (OELs) for the respective contaminant(s). If adequate ventilation cannot be determined or maintained, personnel entering the confined space should be equipped with approved respiratory protective devices."

You guys going into manholes or just regular equipment pits?