194 decibels is the loudest sound that can exist under normal conditions, but you would probably die at 185 dB before you heard it
Benn Jordan explains beautifully in this video not only why 194 dB is the loudest sound that can exist but also a lot of things related to the subject, ranging from the absurdity of the question What is the loudest sound? to the human perception of sound or the explosion of the Krakatoa volcano back in 1883.
The limit of 194 decibels has to do with the fact that from that limit the pressure waves that make up the sound would begin to be destroyed, so it does not make much sense to talk about beyond that value. Value that also, as is well known, refers to a logarithmic scale – albeit a bit that way, as he wisely also points out – and that is directly related to human perception, not to a universal absolute value as in other fields of physics.
The best of all is that he explains it in a very easy to understand way for how complicated the matter is: sound is formed by pressure waves that are transmitted through the air in the atmosphere, an auditory mechanism that converts it into something that our brain can understand, arbitrary scales… He also spices it up at the beginning with the classic: it also depends on what we are trying to measure.
He explains in an agile and informal way complex topics such as the Weber-Fechner Law of the magnitude of physical stimuli and their perception, why the decibel scale does not have an absolute zero (because it is “relative” for each person, although fixed at 0 dB = 20 micropascals for humans) or how there can be louder sounds underwater (up to 270 dB, and that is why whales can communicate over long distances).
Regarding the original question and the 194 dB limit, he also clarifies that for humans from 150 dB it does not matter because it would break your inner ear and at 185 dB you would die from brain damage due to the pressure. The explosion of the Krakatoa eruption was measured at about 100 miles away as 174 dB, and caused the death of about 36,000 people and major damage to many thousands hundreds of miles away, not to mention tsunamis.