It is probably listed as a frame of reference, being the upper end of the scale. 120 is about the level of volume of a jet liner taking off, so this 194 dB would be much higher than that. The reference I have attached mentions the 1883 Krakatoa Volcano eruption as being the loudest sound within the last six to seven thousand years, so mighty in intensity, it was heard from three thousand miles away. Enough smoke and ash were thrown into the air so as to cause shading and optical effects of the sunlight as it was seen in the atmosphere. So my guess would be it is a number assigned to a particular physical phenomenon that represents the upper number of a volume range, while a much lower number, such as one to five dB would represent the minimal end of the volume scale. When I was a young man, just starting out in the teaching vocation and making my first "serious money", I decided to replace the stereo in my car with one that was a huge upgrade in terms of raw power. If I turned the volume knob to approximately the 11 o'clock position (not quite halfway), I could literally feel the entire car vibrating. So this number simply represents what is considered to be a top ranking of a physical phenomenon. It possibly could extend past that, if a large enough phenomenon existed.