TWA is defined as the average of exposure levels over an 8 hour period. No one style or manufacturers line will be acceptable for all employees and all tasks. When the type of hearing protection appropriate for the task has been identified, the Department must supply a few different styles for trial by the employee. The employee must be instructed in the proper wearing of the selected protectors. A supply of hearing protectors must be maintained by the Department.
Ear muffs and ear plugs come in different sizes.
There are major differences in the size of people's heads and ear canals. Many brands of ear muffs are designed with head bands that will not adjust to a smaller head. This type of hearing protection will not hold the ear pieces tightly to the sides of the head and does not make an adequate seal when the band is too large for the wearer. A type of muff designed for small heads should be made available. Most ear plugs are designed to fit in the 'average' male ear canal, and are too large for some men with small ear canals and most women.