This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anaesthetic equipments, Subject name: Anaesthesia
In hyperbaric oxygenation the maximum allowed pressure of O2 is 
Select and explain. 
A. 3 atm, B. 1 atm, C. 5 atm, D. 9 atm
A: 3 atm
Answer: A: 3 atm 
Explanation: At 3 atm, an aerial oxygenation of nearly 2200 mm Hg may be achieved .