Yes
You can buy oxygen cylinders online at http://www.trishir.com/products-details.asp?POID=251 They offer many cylinders of small,medium portable cylinders You can buy small oxygen cylinders at www.oxygenmobility.com For more details call 800-716-6674.
The upstream oxygen sensor is mounted in the exhaust manifold The downstream oxygen sensor is mounted in the exhaust pipe after the catalytic converter
Compressibility. A lot of gas is forced into the cylinders.
The simple answer is ... you don't. A majority of scuba dives use compressed air in the cylinders. Therefore you don't need "oxygen" cylinders. HOWEVER, if you are a diver that is diving on Nitrox, in which divers change the amount of oxygen vs nitrogen in their air, then your tank needs to be "oxygen clean" because you are putting oxygen in first, then nitrogen.
the air becomes rarefied and has a very low oxygen
Because lungs are not adapted to absorb oxygen from the water.
Because they find themselves in environments of little or no oxygen, and oxygen is essential to life.
There are four oxygen sensors one on each exhaust manifold or bank of cylinders and one after each cat for both banks of cylinders
to help with breathing in hot temperatures or when gas or dust is released
leaking oxygen cylinders and liquid oxygen systems in the immediate area
To date (end of 2017) there has been208 climbers who have climbed Mount Everest without using oxygen cylinders (tanks) and 8,098 who have used oxygen cylinders.
A person can get the supply of oxygen for artificial respiration from the cylinders attached to the machines.