Monoplace chambers are Class B chambers built for a single human occupant. The patient is placed in an acrylic tube that is flooded with 100% oxygen and then compressed. Frequently, patients will be given intermittent air breaks to reduce the risk of central nervous system oxygen toxicity (which is extremely low risk anyway). Patients can comfortably watch TV during their dive.
A multiplace chamber is a class A chamber built for multiple human occupants. The chamber is filled with air and compressed while the patients breathe 100% oxygen via hoods or masks. Similarly, patients can receive air breaks. The multiplace chamber has the advantage of having attendants in the chamber to assist in patient care. They are locked in and locked out through a separate, smaller, attached chamber or port.
The use of a multiplace chamber adds the additional responsibility of monitoring the attendant. The attendant is breathing compressed air and therefore is saturating his/her compartments with nitrogen. For the most part, the attendant is diving at “safe depths.” A customary pressure to dive patients is 2.0 atmosphere absolute (ATA). The patient starts the dive at 1 ATA and is compressed to 2.0 ATA or 1 atmosphere or 33 feet of seawater. At this depth, the time limit for a no decompression dive is greater than 3 hours on recreational tables. This is the usual depth used. Attendants will usually lock out long before this time and before nitrogen debt is incurred.