You can usually sense whether the noise around you is excessively loud even without equipment to measure sound.
The sound is excessively loud and might eventually harm your hearing if you or others have to yell to be heard or if you cannot understand each other even when you are arm’s length apart.
The impact of noise on hearing varies with the volume (sound intensity) and duration of the noise (duration).
The best protection is to stay away from loud environments.
If you can’t get away from the noise, make sure you have the right hearing protection.