Dosimeters are devices used to measure an individual's exposure to radiation, noise, vibration and specific chemicals over a specific period of time. Prudent use of dosimeter information assists in adjusting environmental conditions to prevent undesired exposures. Dosimeter results can also be used for medical surveillance and medical treatment. The type of dosimeter will determine how the data collected are used.
Types of Dosimeters
Dosimeters can be active or passive in design. Active dosimeters measure exposure in real time. These instruments have an analog or digital readout of the immediate reading, the cumulative reading, or both. Some active dosimeters will store a history of dosage in a recoverable memory. Passive dosimeters do not provide immediate feedback to the user. Additional analyses or calculation are required to determine the dose.
Dosimeters Measuring Radiation Exposure
Radiation dosimeters are familiar to most people as Geiger-Mueller (GM) meters. The GM meter measures alpha and beta particles and high-energy gamma rays but is not effective in measuring x-ray exposure. A common active dosimeter is a pencil-shaped device with a quartz filament. The filament moves across a directly readable scale showing cumulative dose. Passive dosimeters are used to measure the dose for alpha and beta particles, x-rays and gamma rays. Many people are familiar with the plastic rectangular or hexagonal "badge" worn by doctors, nurses and some scientists. These passive dosimeters contain a film that collects particles and is affected by x-rays and gamma rays and must be sent to a laboratory to be read. Based on the dose information, future exposures can be adjusted to assure the safety of the individual.
Noise-measuring Dosimeters
These dosimeters measure noise levels experienced by an individual or in a particular area, recording the level of sound in decibels (dB). The Time-Weighted Average (TWA) for dB exposure, if not calculated by the instrument, can then be determined and compared to applicable standards to ensure that individuals are not overexposed to high sound levels. The dosimeter readings assist in implementing an appropriate hearing-protection program.
Vibration Dosimeters
These dosimeters can measure the frequency and intensity of vibration transferred to the body over time. The recorded exposures can be compared to recommended standards. This data can help to reduce the potential for nerve and skeletal injury.
Chemical Dosimeters
There is not a single dosimeter to measure all chemicals, nor is there a dosimeter for every chemical. Some instruments will give direct real-time readings. Passive dosimeters collect chemicals on substrates that are sent to a laboratory for analysis. Length-of-stain dosimeters are reagent-containing tubes that change color based upon the time of exposure and the concentration of the chemical. After exposure, the length of the color change is measured on a scale, giving the concentration of the chemical. This amount can then be divided by the time of exposure to determine the dose. The dose can then be compared to established standards to determine if dosages experienced are acceptable.
Purpose of Dosimeters
Data from dosimeters assists in adjusting exposures to assure people's health and safety. The Occupational Safety and Health Administration (OSHA), the National Institute of Occupational Safety and Health (NIOSH) and other government and scientific organizations have established Time-Weighted Averages (TWAs), Recommended Exposure Limits (RELs) and other safe exposure levels.
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