I tried to answer this question together with the other question you had on the fridge. Please look it up.
In summary, in the past, the highly volatile liquid- gas such as ammonia and sulphur dioxide used were very toxic when inhaled, could cause suffocation and also cause reactive airway dysfunction syndrome (RADS), local irritation of the eyes and nose etc. among other serious problems.
Modern refrigerators do not use these gases and the technology continues to improve from toxic gases in the 40s, gases that are known to deplete the ozone layer much later and now to gases that are known to have minimized both negative effects, but still maintaining their function.
Please note that at home, unless you have some sort of accident that will cause a leakage, then exposure to any of those gases is not something to really be worried about 🙂