Detecting a gas leak in a refrigerator isn't always that simple. Newer refrigerators don't use Freon. Modern refrigerators use tetrafluoroethane -- HFC-134a -- a gas that's less harmful to the environment than Freon, a type of chlorofluorocarbon. Freon is known to have a harmful effect on the environment, especially the ozone layer, when leaked into the atmosphere. Leaks can occur when the pipes leading to the compressor are broken or when the seals and gaskets become old and worn. Valves connected by service technicians can also leak if not properly sealed off.
Detecting a freon leak in your refrigerator isn't difficult to do, especially if the leak is fairly substantial. Freon has an odor distinctly different than the oxygen you breathe and can be detected quite easily. However, if you have a slow leak, this may be more difficult to detect. The best way to detect a leak is to contact a service repair person who can use specialized gauges to detect leaks. Because both Freon and tetrafluoroethane are compressed within the refrigerator pipes, a change in pressure will generally be fairly easy to detect.
Leaking freon isn't expected to cause any significant long-term health consequences. If a leak occurs that you can smell, it may only be a short time before all of the gas has leaked out of the refrigerator. These gases are heavier than oxygen and will likely remain below where you would normally breathe, but you may still catch a whiff of the gas. The amount of gas in the refrigerator is limited, so you're not in danger of a continuous leak that will be dangerous in the way that a natural gas leak would be. Instead, once the gas is gone, it will dissipate naturally. If the gas is a CFC, it can contribute to further environmental deterioration.
Many people assume that the failure of the refrigerator to cool properly is related to a gas leak. This common misconception is also made with regard to room and central air conditioners that usually need a simple cleaning. With refrigerators, you need not automatically assume that the lack of cooling is a result of gas loss. Instead, in many cases, the inability of the refrigerator to cool is the result of an electrical component failure. Many other issues are often mistaken for a gas leak. A qualified professional should be able to properly diagnose and isolate the problem.