The chamber in the picture at the original article shows a normal air pressurization unit with the patients breathing oxygen thru masks. In this type of HBOT the risk of fire is greatly reduced. The pressurization is probably less than 2 ATMA (about 30 PSIA). O2 poisoning could be a problem at higher pressures.
HBOT has also been tried as therapy for people with TBI and PTSD with some positive results.
100% O2 under pressure my friend