Semi-welded heat exchangers are the perfect choice for a wide range of refrigeration systems and offer benefits such as excellent heat transfer efficiency, easy capacity expansion and high resistance to fatigue. Ammonia is a common refrigerant and is used in many applications. In some cases operators notice a weak smell when they are very close to the heat exchanger and worry that gaskets may be leaking. In this white paper we will demonstrate that the smell is due to a natural process called permeation and not a faulty gasket. We will also demonstrate that the amount of ammonia released to the surroundings is very low and that it does not cause any harm.