The intensity of sound is measured in decibels (dB) in a scale that ranges from 0 dB (the faintset sound the human ear can detect) to more than 180 dB the noise at a rocket launchpad). Because the decibel scale is lgarithmic, the intessity of noise increase thenfold with each 10-dB increase. Thus, 20 dB has ten times the intensity of 10 dB, while 30 dB is 100 times as intense as 10 dB. A significant cutoff point occurs at 80 dB (roughly the sound of a vaccum cleaner). Sounds of this intensity or louder are considered hazardous to hearing. The longer the ear is exposed to noise, the more damage it causes to hearing. The effect is cumulative and irreversible.

When it is hard to distinguish between the inability to hear because of a noisy enviornment or because of an actual physical impairment, it's time for a hearing test.

P.S. Even moderate levels of noise can prove detrimental to hearing, given enough time.