In one sentence, describe what the following article is about:

Look at the gauge on the regulator and keep an eye out for when the needle starts to drop into the lower numbers. This means that your tank is starting to run out of oxygen and needs to be replaced. Make sure to replace the canister before the needle dips under 200 psi. Oxygen tanks are incredibly flammable and can explode if the tank's air is exposed to an open flame. Do not smoke cigarettes, go near fires, or cook while attached to your oxygen tank. An electrical razor can create sparks, so don't use one when you're attached to oxygen. Contact your doctor and inform them that you're traveling so that they can give you special instructions for your trip. Also, you may need to get another prescription for oxygen if you're taking a longer trip. If you plan on flying, contact the airliner before the day of your flight and let them know that you use an oxygen tank.

Summary:
Change the oxygen tank when it goes under 200 psi. Don't go near any open flames. Call your doctor if you are traveling.