The widely acknowledged criterion for minimizing hearing danger is to expose yourself to 85 decibels for a maximum of eight hours per day, followed by at least ten hours of recovery time at 70 decibels or below (at which the risk of harm to healthy ears is negligible). This should be done without damage to hearing aids or other devices used to reduce exposure to noise. The actual threshold of hearing varies from person to person. However, the average person can detect sounds ranging from 20 dB above normal background levels up to 120 dB when listening with earphones. Sounds above this range require some kind of protection. The human ear can be damaged by loud noises; hearing loss is therefore a common side effect of many forms of occupational sound exposure. Hearing loss can also result from prolonged exposure to lower-level sounds. This type of hearing loss is usually due to aging or disease and cannot be prevented. But it can often be reduced through the use of hearing protectors, such as headphones or earmuffs. Hearing protectors reduce the level of noise that reaches the ear by about 10 dB; thus reducing the risk of damage to hearing ability. Finally, hearing loss may also result from environmental factors outside of our control. These include extremely loud noises such as gun shots, explosions, power tools, and motorcycles; and low-frequency sounds such as wind blowing against a wall or waves crashing on a beach.