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Environmental Health and Safety


Non-Ionizing Radiation / Non-Coherent Hazardous Light

In general, there are two primary hazards to non-ionizing radiation; tissue heating (thermal effects) and photochemical reactions to the skin and retina of the eye. The hazard is dependent on the frequency. Unlike ionizing radiation, frequencies of the electromagnetic spectrum in the non-ionizing region cannot directly ionize particles and cause mutations.

For example, a microwave oven will not cause the same effects as X-rays or gamma rays (ionizing radiation). Microwave radiation primarily causes thermal (tissue heating) effects.

In research laboratories, the primary types of instruments that should be assessed for hazardous non-ionizing radiation energy include any equipment that produces non-ionizing radiation where the source is not fully enclosed. Examples include, but are not limited to, equipment containing an ultraviolet and/or infrared light source that are not fully enclosed (for visible UV and infrared, you can see the light), and equipment such as induction heat sealers or other types of scientific equipment that causes an action in material without directly contacting the material.

Equipment such as high pressure liquid chromatography (HPLC) and spectrophotometers that use light in the infrared or UV wavelengths to detect chemicals generally have light sources that are fully enclosed and do not need to be assessed.

You should refer to the manufacturer’s manual for the equipment. Manufacturer’s should list any hazardous non-ionizing radiation energies that the equipment produces and the protections and enclosures that are provided.

If you are working with equipment where a source of non-ionizing radiation is exposed and you can see the source; or for an invisible source, there is no protective barrier around the source generating the non-ionizing radiation, contact the USC Radiation Safety Office for an evaluation. You can call 803-777-7530 or email radsafe@mailbox.sc.edu to request an evaluation.

Radiation Safety Office staff will evaluate the source and determine, based on guidelines that are published, the most effective administrative or engineering controls to utilize if there are exposures above published guidelines.

A summary of hazards is below along with the guidelines the University typically follows to ensure that exposures are below published guidelines. Refer to the above spectrum chart.

Radiofrequency (RF) Radiation

RF radiation occurs at frequencies below the light frequencies and below infrared light. RF radiation covers the frequency ranges below 300 GigaHertz (GHz). Thermoregulatory and other physiologic changes that a human subject exhibits in response to exposure to RadioFrequency (RF) radiation are dependent on the amount of energy that is absorbed. The term used to describe the absorption of RF radiation is the specific absorption rate (SAR). SAR is the mass normalized rate at which RF power is coupled to biological tissue and is typically indicated in units of watts per kilogram (W/kg).

RF Radiation is divided into 3 subcategories; Sub Radiofrequency, Radiofrequency and Microwave. Two international organizations have published guidelines for exposure to RF radiation; the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the Institute of Electrical and Electronics Engineers (IEEE). The University follows the most restrictive published guidelines of these 2 institutions when evaluating potential exposures to RF radiation and limits. In the United States; the Occupational Safety and Health Administration promulgates limits for RF frequencies between 10 MegaHertz (MHz) and 100 GHz.

Sub Radiofrequency

This band includes RF radiation in the frequency ranges of < 30 kiloHertz (kHz). For RF frequencies less than 300 Hertz (Hz), this band is called Extremely Low Frequency (ELF). RF radiation in this frequency range is typically not produced directly for an action to occur (such as broadcasting radio signals); but is produced by electrical equipment such as cathode ray tubes (older type television sets and computer monitors). In the United States, the alternating current power frequency is 60 Hz and is considered ELF. In other countries internationally, the power frequency for alternating electric current is 50 Hz.

Over the past several years, peer reviewed epidemiological studies have been published claiming a causal relationship between childhood leukemia, and other cancers, with exposure to ELF from power frequency distribution (for example, around power lines and transformers). Several studies have been funded recently to study this relationship; including animal studies. Most every study has not confirmed this relationship. The scientific consensus currently is that there is no conclusive evidence that exposures to ELF fields causes any statistically significant health effects.

Radiofrequency Radiation

This band includes RF radiation in the frequency ranges 30 kHz to 300 MHz. These frequencies are used for broadcast communications including radio, television, cell phones and others. Effects on biological tissue vary with the frequency; but mainly include tissue heating. At lower frequencies of this band, below 100 MHz, induced contact current in the body must also be considered around high power equipment such as transmitters and induction heat sealers to prevent sudden and extreme tissue heating if tissue becomes grounded to an electrical source (known as an “RF” burn).

Broadcast communication towers, satellite communication dishes that transmit signals to the satellite, cellular phone towers and other commercial communications equipment must be approved by the Federal Communications Commission (FCC) in the United States and equivalent governmental bodies internationally. RF fields above guideline limits for the public, as published by ICNIRP and IEEE, only occur at distances very close to tower or broadcast antenna. These areas are secured by a barrier to prevent the public from getting too close.

For communications equipment used by the public, such as cell phones, that transmit and RF field; the FCC and other governmental bodies limit the power that can be maximally transmitted by these devices to limit the specific absorption rate to levels considered safe. All cell phones authorized for distribution to the public must be tested an maximum power to ensure that this SAR limit will not be exceeded. The FCC publishes this information for all manufacturers and models of cell phones sold in the United States.

Typically, research equipment in laboratories do not generate RF fields in this range. Manufacturers are required to test their equipment to ensure that if there equipment does generate residual RF radiation, the RF fields will not cause interference with radio signals. Equipment must be stamped with the “FCC” symbol that verifies their equipment has been tested for interference. If equipment is certified to not cause interference and is stamped with the “FCC” symbol; they will also not cause RF fields above IEEE and ICNIRP exposure guidelines.

Microwave Radiation

This band includes RF radiation in the frequency ranges from 300 MHz to 300 GHz, just below the wavelength of infrared light. The ubiquitous source, of course, is the microwave oven found everywhere. Microwave ovens generate RF frequencies at 2.45 GHz. The United States Food and Drug Administration (FDA), Centers for Devices and Radiological Health (CDRH) publishes limits that manufacturers of microwave ovens must follow and incorporate into their ovens to ensure that a consumer is not exposed to microwave radiation above a limit that would cause an effect. Manufacturers must test and certify the door seals to verify they will not leak microwave radiation above the published limit, and that the interlock that prevents microwave radiation from being generated when the door is open is durable enough to withstand years of normal use and potential damage (i.e. from dropping the oven accidentally) without becoming defective.

Narrow beam broadband communications also utilize the microwave RF frequency band as well as some newer cordless telephones; WiFi communication devices, and many other types of consumer communications products. The primary hazardous effect from exposure above published guidelines is tissue heating; however, exposures above guidelines will occur only very close to the generation source, and the power must be quite high. WiFi and other consumer communications devices operating in the microwave region have very low powers.

There is typically no benefit from microwave radiation in the typical research laboratory except for heat sources. In chemistry laboratories; microwave reaction equipment for heating reaction mixtures has become quite common. This equipment is considered a consumer device and must conform to the CDRH guidelines by the manufacturer.

Non Coherent Light Frequencies (Infrared / Visible / Ultraviolet)

Infrared

As we move to the higher frequencies above RF radiation, the typical convention is to use wavelength, the length between a successive trough of the electromagnetic wave form, rather than frequency (cycles per second). The wavelengths of RF radiation are quite long, at the lower sub-radiofrequency range, kilometers long. But as we move to light and frequencies higher than RF, it is best to refer to them by their shorter wavelength rather than their extremely short frequencies.

The infrared (IR) wavelength spectrum ranges from 780 nanometers (nm) to 1,000 nm (1 millimeter) and is divided into 3 separate bands, IR-A, IR-B and IR-C. IR penetrates the human skin and the eye to various depths ranging from several millimeters by IR-A to superficial absorption of IR-C. Humans have inborn protective aversion responses to pain from high heat and to the bright light that is often also present, so that potentially harmful exposure is avoided. Harmful health effects of IR are due to thermal injury of tissues; primarily tissues of the skin and eyes.

IR heating lamps and other types of devices may be utilized in research laboratories. If exposed to an unenclosed IR lamp or source; USC Radiation Safety should be consulted for an evaluation.

Visible

Visible light is in the wavelength spectrum from 400 nm (very purple) to 780 nm (very red). Visible light sources are not hazardous of course, except at very high intensities where the eye can be damaged.

One exception is intense blue light where a photochemical induced retinal injury (not thermal) can occur between wavelengths of 400 nm and 450 nm. Photochemical induced retinal injury is enhanced for aphakic individual (where the lens of the eye has been removed).

If you are working with exposed intense blue light in this wavelength band; contact USC Radiation Safety for an evaluation.

Ultraviolet

Ultraviolet (UV) radiation is in wavelength spectrum from 100 nm to 400 nm. Like IR, UV is divided into 3 separate bands, UV-A or “blacklight” (315-400 nm); UV-B or “erythemal” (280-315 nm); and UV-C or “germicidal” (100-280 nm). Wavelengths shorter than about 190 nm are strongly absorbed by air. UV is not visible to the human eye, but many broadband UV sources also emit
visible light.

Most exposure to UV radiation comes from sunlight; with approximately 95 % of UV light in the A wavelength band reaching the Earth. The ozone layers absorbs most, but not all, of the wavelengths in the UV-B wavelengths and nearly all of the UV-C wavelengths.

The most hazardous wavelengths of UV radiation to skin and eyes (cornea) is around 270 nm (UV-B). Most all wavelengths in the UV-C band are also harmful; but not as harmful as wavelengths around 270 nm.

Man-made sources of UV radiation include some light sources, such as mercury lamps and UV bulbs and welding arcs. UV from welding arcs can exceed guidelines for harmful UV within seconds.

UV light boxes used to visualize stained DNA gels are common sources of UV in biological laboratories, as well as UV lamps in biosafety cabinets operating in the germicidal UV wavelength band. Polycarbonate plastic is the most effective absorber of UV radiation and should be installed and utilized on UV generated equipment like UV boxes. If working around biological safety cabinets with activated germicidal lamps; ensuring that exposed skin is completely covered, and wearing polycarbonate safety glasses, will most likely be effective protective equipment.

If you are performing any welding operations, personal protective equipment (welder’s mask) and thick, tightly woven protective clothing must be worn. Ensure that the mask is rated for the UV wavelengths generated. An evaluation should be conducted to ensure appropriate protective apparel is worn.

The University follows the UV protection guidelines as published by the American Conference of Governmental Industrial Hygienists (ACGIH).