An odor has been added to your propane gas so you can smell it if it escapes - if there's a leak in the system, for example, or if an appliance malfunctions. But your nose may not always work right.
Some people have a better sense of smell than others.
Some elderly people are unable to detect the odorant in gas. On rare occasions, some people are unable to smell certain odors. Colds, allergies, and sinus congestion can all affect your sense of smell. Tobacco smoke or strong cooking odors can cover up other odors, too - and remember that the use of tobacco, alcohol, or drugs may also affect your sense of smell. Under a special set of rare circumstances, propane gas may lose the distinctive odor that was added.