Microwave exposure limits

Microwave exposure standards appear in several publications. One source is OSHA standards, which limit power density to lOmW/cm for exposure periods of 0.1 hr or more. For exposures shorter than 0.1 hr, the energy density limit is 1 mW-hr/cm, with limited excursions above lOmW/cm. ... 

The American Conference of Governmental Industrial Hygienists pubhshes workplace exposure limits based on power density, electric field strength squared, and magnetic field strength squared for particular frequency bandwidths. This standard includes radio and microwave frequencies. Table 21-2 lists the ACGIH Threshold Limit Values (TLVs), which provide guides for evaluation and control of exposure to radio frequency and microwave radiation. Radio frequency radiation exposures should be as low as reasonably possible. 

The U.S. Federal Communication Commission (FCC) also has exposure limits for microwaves and other radiation frequencies/ FCC standards apply to cell phones and transmission equipment. The cell phone limit is 1.6 W/kg. ... 

Chemical and fine chemical industries are also benefited by the microwave-assisted organic synthesis and a number of organic compounds have been prepared under microwave exposure in limited time. It has proved to be a cleaner, time saving process and that too with good to excellent yields. 

The nature of potential exposure ha2ards of low level microwave energy continues to be investigated (116—118). In the United States, leakage emission from microwave ovens is regulated to the stringent limit of 5 mW/cm at 5 cm (119). There is no federal limit on emission from industrial systems but the IMPI has set a voluntary standard which specifies 10 mW/cm at 5 cm (120). Emission values are equivalent to personnel exposures at several meters, well below limits that had previously prevailed in eastern Europe. This conclusion, derived for microwave ovens, should be vaUd for all microwave systems (121). 

The synthesis of oxygen-heterocycles by intermolecular reactions of a-TK with nucleophiles has received only limited attention. However, a-tosyloxy derivatives of several acetophenones have been prepared by brief exposure of neat HTIB/ketone mixtures to microwave (MW) radiation, and employed on mineral oxide surfaces for microwave-assisted syntheses of thiazoles and 2-aroylbenzofurans 40 (Scheme 11) (98JCS(P1)4093, 99JHC1565). 

Joachim Walter (Boehringer Ingelheim Pharma KG) presented results on the use of microwave technology for virus inactivation in biopharmaceutical products. By using microwaves, viral inactivation can be carried out with the exposure time of the product solution to high temperatures being limited to 500 ms or less. For antibodies, viral inactivation can be effectively carried out using peak temperatures up to 95°C with hold times as low as 5 ms. 

MICROWAVES - This sign must be posted in any area where it is possible to exceed the current occupationally legal limit of exposure to microwave electromagnetic radiation. 

One control to prevent microwave injury is limiting exposure. One can accomplish this by limiting the intensity of microwaves (the frequency or wavelength of an exposure) or... 

What controls will limit exposures to microwaves ... 

Unintentional radiators include industrial applications, such as RF sealers and welders, and microwave ovens. Many such devices have emission standards, promulgated by the FCC, the Food and Drug Administration (FDA), or some other agency, limiting radiation from the device generally to avoid electromagnetic interference (EMI). NIER exposure standards apply to unintentional radiators, as well. 

Microwave procedures are limited by the presence of solvents which reach their boiling points within a very short time (- 1 min) of exposure to microwave. Consequently, high pressures are developed, leading to damage to the vessels material or the microwave oven itself and may occasionally lead to explosion. 

Ideally, companies should have baseline industrial hygiene dataon all routine operations with a potential for chemical, RF/microwave radiation, or ionizing radiation exposures. Even when the industrial hygienist believes the e5q)osure will be well below the allowable limit for an operation, monitoring data is beneficial because ... 

Radiofrequeney (RF)/mierowave radiation is a potential hazard that does not have good warning properties. Therefore, baseline data should be obtained for all routine operations with a potential for RF/mierowave radiation exposure above applieable standards, and baseline RF surveys of new equipment may be required. As a practical matter, a lower frequeney limit needs to be drawn to assess when baseline surveys are neeessary. Since the body is fairly transparent to RF frequencies in the kilohertz region, and standard RF/mierowave radiation meters have a lower limit of 300 or 500 kHz (depending on the meter), 500 kHz is sometimes used as a cutoff for the lower limit for thermal effeets. Most RF/microwave equipment used in semiconductor manufacturing operate at or above a frequency of 13.56 MHz. This equipment includes plasma etchers and ashers, sputtering units, mold pre-heaters, microwave ovens, and plasma enhanced CVD units. 

Because individual susceptibility varies widely, an occasional exposure of an individual at (or even below) the threshold limit may not prevent discomfort, aggravation of a preexisting condition, or occupational illness. In addition to the TLVs set for chemical compounds, there are limits for physical agents, such as noise, microwaves, and heat stress. 

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