initially to determine which areas are higher than 80 dB A. For these areas, an official sound survey will take place. This type of survey is normally completed using a sound level meter (SLM). A sound level meter takes a measurement of the sound present in the environment at that moment. There are three types of sound level meters. Type 0 is a precision instrument normally used in laboratories. Type 1 is for precision measurements taken in the field. Type 2 sound level meters are less precise than type 1 and are often used to take all-purpose sound level measurements. There are also noise dosimeters that are worn on the body and measure the amount of noise exposure an individual receives over a given time period. OSHA guidelines state that either a SLM or noise dosimeter may be used for sound monitoring. Surveys must be repeated when there are significant changes in machinery and/or processes that would affect the noise level. Engineering and administrative controls Engineering controls and administrative controls are ranked as the most effective protection from noise in the hierarchy of controls. Engineering controls are measures taken to reduce the intensity of noise at the source or between the source and a person exposed to the noise. This can be done by choosing tools that make less noise, installing a barrier between the worker and the noise, enclosing the machinery all together, or making sure the machinery is maintained properly (lubricating equipment)..Administrative controls are limitations around noise sources that limit length of noise exposure. Some known methods are running loud equipment when less workers are present, controlling the amount of time a worker is allowed around the noise source, constructing areas that allow employees a chance to escape from the noise (a sound proof room to give recovery time), or increasing the distance between the worker and the excessive noise source. Hearing protection devices If engineering controls fail to maintain an 8-hour time-weighted average below 85 dBA, then a hearing protection device (HPD) is required. There are two general types of HPDs: earplugs and earmuffs. Each one has its own benefits and drawbacks. The selection of the proper HPD to be worn is commonly done by an industrial hygienist so that the proper amount of noise protection is worn. OSHA requires that HPD be given free of charge. Earplugs There are four general classes of earplugs. These include: