Introduction
Radiation is a form of energy transmission, in many cases imperceptible to the senses, and is considered a physical pollutant. However, when radiation interacts with matter, it can generate changes in it, producing, for example, an increase in temperature or its ionisation. When the matter is the human body, these alterations can cause different health effects, the type and severity of which depends on, among other parameters:
- The type of radiation.
- The “quantitat” of received radiation
The quantities used to correlate radiation with the biological effects it can produce are the dose and the energy flux rate:
- The magnitude dose, which refers to the energy deposited by the radiation per unit mass of the tissue in which it is deposited, is usually expressed in units of J/kg.
- The magnitude of the energy fluence rate is defined as the power of the radiation beam divided by the beam cross-section, and is therefore usually expressed in W/m2.
Depending on the nature of the radiation, a distinction can be made between the following:
- Corpuscular, which have a certain mass at rest.
- No corpuscular, being merely a form of energy. As for corpuscular radiations, they are fundamentally particles that emerge from the atom with great speed. In most cases these particles come from transformations suffered by the nucleus of the atom. As for non-corpuscular radiations, they can be of different types:
- mechanical, which needs a material support for its propagation (as is the case of sound)
- electromagnetic, which can be propagated both through a material medium and also through the vacuum.
Nature of electromagnetic radiation
The radiation we are dealing with is made up of electromagnetic waves that are formed by the simultaneous existence of a magnetic field (H) and an electric field (E), perpendicular to each other and perpendicular to both in the direction of wave propagation. In waves, the initial magnetic field, which varies over time, generates an electric field, which also varies over time. Aquest camp elèctric genera un altre camp magnètic semblant a l’inicial. As this process repeats itself, the energy spreads at the speed of light. When it propagates in a vacuum, this speed, c, is in the order of 3-108 m/s (in one second it travels 300,000 km). When it propagates in the air it practically has this same speed, whereas when it propagates through a material medium it suffers a certain decrease in its propagation speed.
The amplitude of both the electric field and the magnetic field varies sinusoidally.
The frequency, f, is the number of complete oscillations it carries in one second, so its units are s-1, which is also called hertz (Hz). Es denomina longitud d’ona, l, a la distància que hi ha entre dues oscil·lacions completes. Thus, the result of the product between the number of complete oscillations that are carried out in one second (f) and the distance (travelled in each of these complete oscillations) is the distance that the radiation travels in one second:
c = 3·108 m/s = f · l
The period, T, is defined as the time required for a complete oscillation to take place. If f is the number of complete oscillations that are carried out in one second, it follows that the time required to carry out a single complete oscillation, T, is defined by T=1/f.
The basic and unitary component of electromagnetic radiation is called the photon. By means of quantum mechanics it is possible to model the different modes of behaviour of the photon, which in certain phenomena behaves as if it had a corpuscular nature, while in the majority of phenomena it shows a clearly wavelike nature. The energy, E, of the photon is proportional to the frequency of the photon. The constant of proportionality, h, is called Planck’s constant and is 6.6-10-34 J-s. Thus, E = h · f.
The matter with which electromagnetic radiation can interact is made up of molecules, which are also made up of certain combinations of atoms. At the same time, the atom is made up of a nucleus and a series of electrons. Applying the simile of the planetary model, the electrons trace orbits around the nucleus, needing an external contribution of energy to leave this orbit and move to an orbit of higher energy (atomic excitation process), and may even become detached from the atom (ionisation process). If the incident photon has enough energy to “pull” (ionise) an electron from the atom, it is called ionising radiation. The simplest atomic structure is that of hydrogen, which consists of a single electron orbiting around the nucleus. The minimum energy required to start this electron is in the order of 2-10-18 Joules. Electromagnetic waves that do not have this energy are said to be non-ionising.
From the relation E = h · f, it follows that non-ionising radiation has a frequency of less than 3·1015 s-1 . From the relation c = 3·108 m/s = f – l, it follows that the non-ionising radiation mentioned above has a wavelength greater than 9.9·10-8 m.
Depending on their energy (depending on the frequency or wavelength), electromagnetic radiation has different ways of interacting with the material medium, which leads to the following classification.
Extremely Low Frequency and Static Fields (ELF)
As a static magnetic field of natural origin, we could indicate the terrestrial magnetic field.
Within the group of extremely low frequencies, electric fields originating both from the electricity distribution network and from equipment connected to this network predominate. In all this group the frequency is 50 s-1, since it is an alternating current, which performs 50 complete cycles in 1 s. Originally, display screens contributed to the generation of electromagnetic fields, although nowadays they are low-emission, in accordance with the electromagnetic field compatibility regulations.
| demonization | Frequency | Wavelength | Energy |
|---|---|---|---|
| Extremely Low Frequency (ELF) | 0 to 30 kHz | l >10 km | 0 J to 2·10-29 J |
Radio Frequencies (RF)
These are the frequencies most commonly used in both radio and television broadcasting.
| Designation | Frequency | Wavelength | Energy (J) |
|---|---|---|---|
| Low frequency (LF) | 30 kHz to 300 kHz | 10 km to 1 km | 2·10-29 to 2·10-28 |
| Freq. Medium Frequency (MF) | 300 kHz to 3 MHz | 1km to 100m | 2·10-28 to 2·10-27 |
| High Frequency (HF) | 3 MHz to 30 MHz | 100m to 10m | 2·10-27 to 2·10-26 |
| Very high freq. (VHF) | 30 MHz to 300 MHz | 10m to 1m | 2·10-26 to 2·10-25 |
Microwave (MO)
UHF is used in television broadcasting.
Mobile telephony operates at frequencies between 400 MHz and 900 MHz as well as 1800 MHz.
Microwave ovens heat the materials by stirring their molecules. Each type of material requires a certain frequency to provoke this agitation (molecular resonance frequency). In the case of domestic microwave ovens, the material to be heated is water, operating at a frequency of 2.45 GHz.
| Designation | Frequency | Wavelength | Energy (J) |
|---|---|---|---|
| Ultra High Freq. (UHF) | 300 MHz to 3 GHz | 1m to 0,1m | 2·10-25 to 2·10-24 |
| Super high Freq. (SHF) | 3GHz to 30GHz | 100mm to 10mm | 2·10-24 to 2·10-23 |
| Extrem. High Freq. (EHF) | 30GHz to 300GHz | 10mm to 1mm | 2·10-23 to 2·10-22 |
Infrared (IR)
The human being emits electromagnetic radiation in this band, by dissipating heat by radiation. Night vision systems are based on equipment that makes it possible to see this radiation that is outside the visible spectrum. Furthermore, infrared radiation is also manifested in the use of surface heating lamps, as well as in materials that are at high temperature (foundries).
| Designation | Frequency | Wavelength | Energy (J) |
|---|---|---|---|
| IR-C | 300 GHz to 100 THz | 1 mm to 3 µm | 2·10-23 to 6,6·10-20 |
| IR-B | 100 THz to 214 THz | 3 µm to 1,4µm | 6,6·10-20 to 1,4·10-19 |
| IR-A | 214 THz to 385 THz | 1,4µm to 780nm | 1,4·10-19 to 2,5·10-19 |
Visible
The sun is the most important natural source of electromagnetic radiation. Its frequency range includes from part of the IR to part of the UV, covering the entire visible range (from red to violet).
| Designation | Frequency | Wavelength | Energy (J) |
|---|---|---|---|
| Red | 385 THz to 463 THz | 780nm to 647nm | 2,5·10-19 to 3,1·10-19 |
| Orange | 462 THz to 513 THz | 647nm to 585nm | 3,1·10-19 to 3,4·10-19 |
| Yellow | 513 THz to 522 THz | 585nm to 575nm | 3,4·10-19 to 3,5·10-19 |
| Green | 522 THz to 611 THz | 575nm to 491nm | 3,5·10-19 to 4,0·10-19 |
| Blue | 611 THz to 707 THz | 491nm to 424nm | 4,0·10-19 to 4,7·10-19 |
| Violet | 707 THz to 750 THz | 424nm to 400nm | 4,7·10-19 to 5,0·10-19 |
Ultraviolet (UV)
UV radiation is used in germicidal lights (UV-C), phototherapy lights, solar simulation lights (UV-A and UV-B), photocopiers (UV-A and UV-B), contrast lights (black light, UV-A) or graphic arts. Fluorescent lamps also have a certain UV-A component. In the generation of electric arcs, there is also an important contribution of UV-A and UV-B component. Remember that the energy needed to ionise an atom is 2.10-18 J, so we can see that part of the UV-C radiation is non-ionising, but that the range of energies between 2.10-17 and 2.10-18 J is ionising radiation.
| Designation | Frequency | Wavelength | Energy (J) |
|---|---|---|---|
| UV-A | 750 THz to 952 THz | 400nm to 315nm | 5,0·10-19 to 6,3·10-19 |
| UV-B | 952 THz to 1071 THz | 315nm to 280nm | 6,3·10-19 to 7,1·10-19 |
| UV-C | 1071 THz to 30 PHz | 280nm to 10nm | 7,1·10-19 to 2,0·10-17 |
X-rays and gamma rays (RX and gamma)
Some nuclei of atoms can be in an excited state, and spontaneously tend to de-excite, where their excess energy can be released in the form of electromagnetic radiation, with the emission of the corresponding gamma photon. When the de-excitation is on the scale of the atom’s electrons, the radiation is called the characteristic x-ray. Alternatively, braking x-rays can also be produced by abruptly changing the velocity of electrically charged particles propagating through a material medium. In all these cases we are dealing with ionising radiation.
Effects of radiation
The types of biological effects that non-ionising radiation can produce depend fundamentally on the type of interactions that this radiation causes in the biological tissues affected. The following table shows the most significant interactions according to the radiation involved.
| Frequency or wavelength range | Type of interaction |
|---|---|
| ELF and below radio frequencies (from 0 s-1 to 10 kHz) | Induction of electric currents |
| Radiofrequencies and Microwaves (up to 300 GHz) |
Induction of electric currents Absorption as rotational and vibrational energy of molecules that are transformed into heat. |
| Infrared Radiation (1 mm > l > 780 nm) | Absorption as rotational energy of the molecules, which is transformed into heat. |
| Visible and Ultraviolet Radiation A, B and C (780 nm > l > 100 nm) | Absorption as photochemical energy and heat |
| Electromagnetic radiation with l < 100 nm | Ionisation of atoms and molecules |
In more detail, the effects that can be produced by the so-called optical radiation, which covers the entire spectrum of IR, visible and UV radiation, are caused by:
| Frequency or wavelength range | Eyes | Skin |
|---|---|---|
| Ultraviolet-C l = 180 to 280 nm | Photokeratilis (cornea) | Erythema. Accelerated skin ageing. Increased pigmentation of the skin. |
| Ultraviolet-B l = 280 to 315 nm | Photokeratilis (cornea) | Erythema. Accelerated skin ageing. Increased pigmentation of the skin. |
| Ultraviolet-A l = 315 to 400 nm | Photochemical cataract (Crystallium) | Darkening of pigments. Photosensitization reactions. Skin burns. |
| Visible l = 400 to780 nm | Photochemical and thermal lesions in the retina | Darkening of pigments. Photosensitization reactions. Skin burns. |
| Infrared-A l =780 to1400 nm | Cataract, retinal burns | Skin burns |
| Infrared-B l = 1400 to 3000 nm | Cataracts, corneal burns | Skin burns |
| Infrared-C l =3 µn to 1mm | Corneal burns | Skin burns |
Regarding static electromagnetic fields and ELFs, there is currently no conclusive information available. The available data is based on:
- Static and time-varying magnetic fields induce internal forces that oppose the circulation of moving ions and can, for example, vary the speed of blood flow.
- ELF waves, emitted in pulses of short duration and high intensity, can induce electrical currents of a certain density in muscles and other tissues, which directly stimulate muscle and nerve cells.
- Magnetophosphenes”, characterised by the appearance in the visual field of flax-like lights that disappear when exposure ceases, are probably due to the presence of induced currents that provoke a certain stimulation of the optic nerve or retina.
- The presence of magnetic fields and electromagnetic waves of ELF (and higher frequencies) can affect the functioning of cardiac pacemakers, both through the induction of forces on magnetisable components of the pacemaker, and through the interference that electromagnetic waves can exert on the electrical functioning of the device.
- In the presence of high magnetic fields, metal prostheses (magnetisable material) can be subjected to forces that modify their situation and function.
Maximum admissible values
The CENELEC (European Commission for Electrical Standardisation) has two regulations:
- ENV 50166-1. “Human exposures to electromagnetic fields from 0 Hz to 10 kHz” and
- ENV 50166-2. “Human exposures to electromagnetic fields from 10 kHz to 300 GHz”. In addition, more recently, the International Commission on Non-Ionizing Radiation Protection (ICNIRP), issued in 1998 a Guide with the recommended exposure limits for exposure to electric, magnetic and electromagnetic fields, for frequencies up to 300 GHz.
Furthermore, the recommendations in this field give rise to the corresponding recommendations of the Council (1999/519/EC, Council Recommendation of 12 July 1999 on the exposure of the general public to electromagnetic fields – Official Journal of the European Communities L199, p. 59-70).
The limits indicated in these documents, regarding H, B and E levels or daily exposure time, are based on the prevention of effects such as those mentioned so far, but there is also a growing concern about the role played by electromagnetic waves in the generation of cancerous processes. Although this concern has been known and accepted for some time for ionising radiation, it has been awakened in recent years with regard to extremely low frequency electromagnetic waves (ELF) and also microphones.
In this context, several epidemiological studies, carried out mainly in Sweden, the United States, Great Britain and Canada, relate the appearance of different types of childhood leukaemia to residential exposure to 50-60 Hz ELF waves from AC power lines, as well as to other types of cancer (cervical) in electrical company workers. These studies find a higher incidence of these diseases in exposed populations than would be expected in similar unexposed populations, relating the biological mechanism to the presence of magnetic fields of flux density “B” as low as 0.3 µT and with a frequency of 50 Hz or 60 Hz. In ENV 50166-1 (up to 10 kHz), the maximum predictable values have been established fundamentally to avoid induced currents inside the body, cardiac arrhythmia and its adverse effects.
In this context, reference values are given for both the electric and magnetic fields:
Reference values for the electric field
0 – 0,1 | 42 | |
| 0,1 – 50 | 30 | t £ 112/E |
| 50 – 150 | 1500/f | t £ 80/E |
| 150 – 1500 | 1500/f | t £ 80/E |
| 1500 – 10000 | 1 |
Reference values for the magnetic field
| 0 – 0,1 | |
| 0,1 – 0,23 | |
| 0,23 – 1 | T 1,4 T 320/f mT320/f2 mT80/f mT |
| 1 – 4 | 0,053 mT |
| 4 – 1500 | |
| 1500 – 10000 |
In open space and with biological materials 1 A/m = 4·P ·10-7 T.
There are various work areas in which exposure to electromagnetic radiation in the range of RF and MO can occur: paint drying, certain techniques in the field of physiotherapy, electrical welding processes.
Within this range of frequencies, we must also bear in mind the very extensive use of mobile telephony, which operates in the MO range. The fundamental characteristic of these radiations in their interaction with biological tissues is the transformation of the energy they transmit into heat. The energy absorbed per unit of mass of biological tissue and per unit of time is called the Specific Absorption Rate, known by the acronym SAR.
This energy absorption is manifested in an increase in the temperature of the irradiated tissues. At frequencies below 30 MHz, surface absorption dominates in the area of incidence of the radiation. Standard ENV-50166-2:1995 considers that, below a SAR value of 4 W/kg, it is difficult for adverse health effects to occur due to an increase in tissue temperature, therefore the radiation levels proposed as maximums are those resulting from applying a safety coefficient to this value. In the case of occupational exposure, the safety factor is 10, so that the SAR value is 0.4 W/kg; for the general public, and above the latter limit, the factor applied is 5, in which case the SAR value is 0.08 W/kg. From these values, the values of the intensity of the electric field “E”, the intensity of the magnetic field “H” and the density of the magnetic flux “B” or the power density of the wave, necessary for the corresponding SAR to be less than 0.4 W/kg in occupational exposures, are estimated.
Thus, for the range from 10 kHz to 300 GHZ the reference values given by the ENV-50166-2 standard, in addition to indicating maximum values for the electric field and for the magnetic field, also indicate maximum values of the energy flux rate S, (power per unit area of the radiation source, expressed in units of W/m22). The table below details these reference values:
| 0,01 – 0,038 | 1000 | 42 | |
| 0,038 – 0,61 | 1000 | 1,6/f | |
| 0,61 – 10 | 614/f | 1,6/f | 10 |
| 10 – 400 | 61,4 | 0,16 | f/40 |
| 400 – 2000 | 3.07 f½ | 8.14 · 10-3 f½ | 50 |
| 2000 – 150000 | 137 | 0,364 | 3.334 · 10-4 f |
| 150000 – 300000 | 0.354 f½ | 9.4 · 10-4 f½ |
The supply of thermal energy to the different parts of the body can cause damage, especially to organs with less blood supply, as they are less able to dissipate heat. This is why testicles, which can be particularly sensitive, can affect sperm production.
Some authors indicate a possible correlation between exposure to radiofrequencies and microwaves and the existence of an affectation of the nervous system, known as neurasthenic syndrome (headaches, anorexia, tiredness, confusion, tremors, insomnia).
From the point of view of prevention, it must be borne in mind that the presence of electromagnetic fields can have an impact on the electrical functioning of pacemakers or on their programming. The pacemaker is a detector of the electrical activity of the heart and can be “tricked” by the presence of radiofrequency signals and confuse this signal as coming from the heart, thereby decreasing its aid activity. Some pacemakers incorporate a frequency filter that prevents this effect. Although the manufacture of these electromechanical devices takes into account their protection against the action of this type of radiation, there is a residual risk for the wearer, the magnitude of which is not known. Because of this uncertainty, the risk and prohibition of access to areas where such radiation is present must be visibly indicated. It should also be noted that other materials or mechanisms introduced into the organism may be affected by the presence of electrical, magnetic and electromagnetic fields, such as neurostimulators, metal prostheses, etc.
Laser radiation
This is a specific case of optical radiation, being systems that emit electromagnetic radiation in a narrow wavelength band (monochromatic), corresponding to optical radiation (ultraviolet, visible and infrared). The waves that form the laser radiation are in phase and travel in a certain direction (beam direction), with very little angle of divergence. These characteristics of lasers make it possible to concentrate a high density of energy on the desired surfaces.
The amount of energy that a laser is capable of transmitting depends on the power of the laser. Both this and the emission wavelength depend on the active medium, which is a set of atoms or molecules with certain energy levels, so that if their electrons are excited by an external energy source (pumping system), they subsequently emit a certain amount of energy when they return to their original levels. This energy characterises the laser and serves to identify it.
The use is extensive: bar code readers, surgery, therapy, metallurgical industry, military applications.
The maximum level of exposure to laser radiation to which an individual may be subjected on the skin or in the eyes is known as maximum permissible exposure (MPE). The lasers that cover the EMP in the shortest time are those with the highest emitting power. In this context, the philosophy of risk prevention is based more on accident prevention criteria than on occupational illnesses, since in a very short period of exposure they can cause both reversible and irreversible damage.
Depending on both its power and power density (W/m2) of their beam, lasers are classified into:
- Class 1: these are the so-called intrinsically safe lasers, in which there is no possible mode of operation in which the maximum permissible exposure can be exceeded.
- Class 2: they have low output power, not exceeding 1 mW. They are not intrinsically safe, as eye protection is based on the closing reflexes of the eye.
- Class 3A: they have a maximum output power of 5 mW and a power fluency of no more than 25 W/m2, This limits the maximum power incident on the eye to 1 mW (considering that it has an aperture diameter of 7 mm). The vision of the beam with the aid of optical instruments can be dangerous.
- Class 3B: that when operating in continuous emission cannot exceed 0,5 W, while for pulsed lasers the radiant exposure must be less than 105 W. J/m2.
- Class 4: these are those that exceed the maximum conditions of Class 3B.
All laser equipment must be correctly identified with the corresponding label identifying the corresponding class and the precautions to be adopted for its use.
A very popular use nowadays is the use of laser pointers. When making indications in images and information on a screen, for example in training sessions. As technical work equipment, they are subject to equipment safety legislation, and their commercialisation is regulated. The European standard applicable to the manufacturer is EN 60825-1, according to which they can only be Class 2 lasers, therefore, with a maximum power of 1 mW. The protection is based on the consideration that in case of incidence of the beam, the closing of the eyelids would take no more than 0.25 seconds. When purchasing a laser pointer it is necessary to ensure that it is correctly classified as Class 2 according to the EN 60825-1 standard.
Bibliography
- International Commission on Non-Ionizing Radiation Protection
. From this website you can download the “Guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields (up to 300 GHz)”. - Council Recommendation of 12 July 1999 on the exposure of the general public to electromagnetic fields (0 HZ to 300 GHz). 1999/519/CE. Official Journal of the European Communities. L 199 from p. 59 to 70.
- CENELEC, ENV 50166-1. “Human exposure to electromagnetic fields from 0 Hz to 10 kHz”. CENELEC, 1995.
- CENELEC, ENV 50166-2. “”Human exposure to electromagnetic fields from 10 kHz to 300 GHz”, CENELEC, 1995.
- Basic concepts on the fundamentals of electromagnetic fields, prepared by Lawrence Livermore National Laboratory.
- Council on wireless technology impacts.
- Algunas cuestiones sobre seguridad láser, Madrid, INSHT, 1996.