Are we talking a mono or multi place chamber? In a mono place, any outside air is replaced with 100% O2 about 20 mins after pressurizing. The only humidity in the chamber at this point is coming from your patient (exhaling, off gasing). We do monitor our chamber room humidity and the goal is to keep the area 40% minimum humidity levels. In the winter this can be challenging. If I feel we have too much static in the room and consequently in chamber first part of tx, I will often saturate a towel with water and put in chamber on gurney platform. You can also wet the patient's hair, although some don't care for this practice.
You can also purchase a floor a non conductive floor wax which actually traps and releases moisture. We purchased ours from ATMO Intl. You can find them at www.hyperbaricmedicine.com
I hope this helps.