Permanent hearing loss is the main health concern. In heavy industrial and manufacturing environments, as well as other situations such as farms, cafeterias, or bars. Noise is one of the most common occupational health hazards. Why is noise an important workplace hazard? It is also very delicate: this is why loud sound may damage hearing. The hearing mechanism in the ear is sensitive enough to detect even small pressure waves. Even very loud sounds produce pressure fluctuations which are extremely small (1 in 10,000) compared to ambient air pressure (i.e., atmospheric pressure). The brain interprets the information as sound. The hearing mechanism of the ear senses the sound waves and converts them into information which it relays to the brain. Table 1 Approximate Speed of Sound in Common Materials In gases, the higher the velocity of sound, the higher the pitch will be (Remember the 'Mickey Mouse' sound when people talk after inhaling helium gas?). Table 1 lists the approximate velocity of sound in air and other media. These pressure variations travel through the air as sound waves ( Figure 1). Thus, as the drum surface vibrates, it creates alternating regions of higher and lower air pressure.

When the surface moves in the opposite direction, it creates a negative (lower) pressure by decompressing the air. This creates a positive (higher) pressure by compressing the air. As it moves forward, it pushes the air in contact with the surface. The drum surface vibrates back and forth.

To illustrate, imagine striking a drum surface with a stick. These air pressure changes travel as waves through the air and produce sound. When an object vibrates, it causes slight changes in air pressure. Sound is produced by vibrating objects and reaches the listener's ears as waves in the air or other media. In either case, it can be hazardous to a person's hearing if the sound is loud and if they are exposed long and often enough. Rock music can be pleasurable sound to one person and an annoying noise to another. The difference between sound and noise depends upon the listener and the circumstances.

Where is the sound coming from