Final answer:
Medical gases used in hospitals for patient care, like oxygen and anesthesia, are regulated and require proper authorization for purchase. Gases used for welding or fueling barbeque grills also have safety regulations for their handling and purchase.
Step-by-step explanation:
Medical gases, such as oxygen and anesthesia gases used in hospitals, are critical for patient care and cannot be purchased 'willy-nilly' without proper authorization. These gases are regulated by health authorities and require prescriptions or licenses for purchase. Compressed acetylene and oxygen mixtures for welding, and compressed propane for barbeque grills, while more easily accessible, also have safety regulations for handling and purchase.
Due to the potential dangers associated with the improper use of compressed gases, there are strict regulations in place to control their sale and distribution. Proper handling and usage instructions are paramount to ensure the safety of all users, and as such, these materials are not available for casual purchase by the general public.