A decibel is the measurement of sound, one-10th of a bel, that is used most commonly to measure everyday sounds. You will most often encounter the word "decibel" in conjunction with charts. You can use these charts to determine which decibel levels are safe, and which can cause physiological damage after prolonged exposure.
0 to 30 Decibels
Sounds from 0 to 10 decibels are the lowest that you can possibly hear. In fact, if you hear a sound that is lower than 10 decibels you will likely have a hard time knowing whether it was real or imagined. For instance, a normal light bulb hum comes in at around 15 decibels. In comparison, 30 decibels is around the sound of the human whisper. These low-level decibel sounds are typically easy for those with normal hearing to detect and pose no risk to hearing.
60 to 90 Decibels
When you converse normally, you are speaking in the 60 to 70 decibel range. This is also around the decibel range of birds chirping heard from about 10 feet away and many small machines such as the electronic shaver and electric fan. Many musical instruments are intentionally designed to play at this decibel level, such as the piano and the guitar, though of course, you can make these instruments play at louder levels if you wish. Sounds that you may come in contact with at the 90 decibel level are from the subway, farm tractors and city traffic. Prolonged exposure to sounds at this level poses no risk to hearing.
95 to 115 Decibels
Sounds that you may encounter at the 95 decibel level include power mowers, motorcycles, factory noise and applause in a large auditorium. Going into the low 100s, you would encounter sounds like a large rock concert, a sand blaster, printing press and train. Conversation at these decibel levels becomes difficult. In fact, you can damage your hearing if you allow prolonged exposure to sounds at this level. Of course, it is possible to expose yourself to these decibel levels with headphones as well.
125 to 155 Decibels
You can cause pain to yourself at these decibel levels with short-term exposure and hearing loss with longer-term exposure. Sources of these high decibel levels include an amplifier within 5 feet, a shotgun, drag car racing, a cymbal crash and emergency vehicle sirens. You will experience pain or ringing from these sources almost immediately. The threshold at which the eardrum breaks instantly is 160 decibels. Sounds significantly louder than this can kill because of the strong air pressure waves that they consist of. Sounds of this magnitude are typically created in explosions and are well beyond the range of human hearing.