"0 dB"
Does anyone here realize that the decibel scale is logarithmic, not linear? It is a ratio of a measured quantity to a reference quantity.
That means that there IS a possibility of negative dB numbers. However, virtually any indoor environment (home, office) is far noisier than "zero dB" (which is defined as a sound pressure level of .0002 microbars), generally because of lighting, appliances, HVAC, traffic, outdoor wind noises, animals, etc.