Military Hygiene and Hygiene in Emergency Situations - K.O. Pashka 2005

Occupational hygiene of military personnel during the mitigation of emergency consequences and in wartime
Occupational hygiene of military personnel in radio-technical troops

Occupational hygiene at radar stations (radars)

Mobile and stationary radar stations¹ are in service with practically all Branches of the Armed Forces of Ukraine. They are designed to detect invisible objects using radar Methods. The principle is that various objects on Water, land, or in the air are subjected to pulsed irradiation by ultra-high frequency (UHF) radio waves, which are reflected from their surfaces, captured by the antenna, pass through the waveguide into the receiver, where they are amplified and converted into a low-frequency signal. The latter is fed to the indicator screen as a glowing dot or a sweep trace. Based on its characteristics, the operator can determine the Location, size, contours, speed, and direction of movement of the detected object. The main elements of a radar include: an antenna system, radio transmitting and receiving equipment, anti-jamming equipment, output devices (indicators), computers for controlling radar operation and signal Processing, and power supply sources.

¹ A radar station is equipment for detecting and recognizing various objects (targets), determining their coordinates, and obtaining information about them using radar methods.

The energy accumulated by the modulator in the intervals between generation pulses is fed as high-voltage pulses to the UHF field generator, which acts as the energy transmitter to the antenna. Usually, the generator and the UHF pulse receiver are housed in a single unit shielded by a metal coating. The duration of UHF pulses is measured in microseconds, the power in hundreds of kilowatts, and the propagation speed reaches up to 300,000 km/s.

Radars are classified: by location method - active, semi-active, and passive; by location site - ground-based, shipborne, airborne, satellite, etc.; by type of radiation - pulsed (discrete) and continuous (quasi-continuous) wave; by operating wavelength range - meter, decimeter, centimeter, and other ranges; by purpose - target detection, reconnaissance, weapon control, flight support, meteorological and navigational support, etc.

The territory where a radar is located is called a technical site or position. The radar antenna can operate stationary—in the mode of continuous tracking of a single sector; in this case, a constant UHF field is created in that direction, continuously acting on the object. In the case of circular surveillance or scanning (sector scanning), the antenna moves in specified directions, and the object is irradiated by an intermittent UHF field only periodically.

Due to the fact that a radar antenna creates maximum radiation intensity in one direction while it is barely detectable in another, the angular distribution of the antenna's radiation intensity is highly uneven. A plotted graph showing the dependence of the UHF field intensity on the antenna's radiation angle is called the directivity pattern of the radiator.

Exposure to UHF radio waves most frequently affects individuals who, for various reasons, enter the sector of the UHF field created by the radar antenna without being directly involved in radar operation. Such cases occur due to failure to maintain safe distances from residential or industrial buildings when selecting the radar technical site (position), or

during combat operations when military units of different branches of the armed forces interact. Specialists who service these installations are usually exposed to the UHF field only if safety regulations are violated during radar maintenance or As a result of an emergency.

The station's operating personnel—technicians, operators, and diesel mechanics—are headed by the radar commander. Station alignment and repair are carried out by radio workshop specialists. Their working conditions are affected by unfavorable factors that can be divided into specific and nonspecific. Specific factors include, for example, pulsed electromagnetic UHF radiation, the sources of which are antennas, the generator (if the metal cover has been removed for adjustment or repair), poorly connected or disconnected waveguide flanges, and radiation through unsealed openings of the transceiver unit housing.

Nonspecific factors include soft X-ray radiation, noise and vibration from the diesel engine, exhaust gases and other harmful chemical impurities in the indoor air, unfavorable air Temperature, the sedentary nature of operators' work in conditions of insufficient lighting accompanied by significant neuro-emotional and visual strain.

Typically, personnel are affected by individual factors from this list or a combination of several of them. For instance, diesel mechanics are exposed to vibration, noise, exhaust gases from the running engine, fuels and lubricants, etc. The radar commander, technicians, as well as the engineering and technical staff of radio workshops may be exposed to the UHF field and soft X-ray radiation. Operators working at indicator screens inside the radar cabin are affected by factors such as maintaining a sedentary posture during shifts in a quiet, monotonous environment with almost a complete absence of external stimuli, while simultaneously experiencing the strain of such mental Functions as continuous attentive Visual Perception of information, memorization, and rapid analysis followed by an immediate report to a superior officer. These circumstances contribute to fatigue development and a decrease in operators' performance.

BIOLOGICAL EFFECTS OF UHF radiation and protection against it

The biological effect of a UHF field is determined by the penetrating capacity of microwaves into the Organism, their selective interaction with Tissues, power, duration of exposure, and the size of the irradiated surface. The depth of its penetration into the body is approximately 1/10 of the wavelength and reaches: for millimeter waves—the upper layers of the Skin; centimeter waves—subcutaneous adipose tissue and Muscles; and decimeter waves—Internal Organs. Under otherwise equal conditions, the latter pose the greatest danger to The Human Body subjected to irradiation. The absorbed energy causes local tissue heating and an increase in the overall body temperature. A distinctive feature of UHF radiation is the selective heating of tissues containing high amounts of water, unlike, for example, infrared rays, which heat all tissues uniformly. The biophysical mechanism of UHF field energy absorption and its conversion into heat occurs through the interaction of electromagnetic oscillations with body molecules or their aggregates, as a result of which the field energy penetrating the body causes the heating of body tissues.

The degree of absorption depends on the intensity and frequency of the field, exposure duration, thermoregulation efficiency, body and field configuration, as well as the dielectric properties of tissues. Tissue heating can lead to Protein Denaturation and coagulation, increased Cell membrane permeability, decreased enzyme activity, and an accelerated rate of Chemical Reactions. If body temperature exceeds 40 °C, Central Nervous system dysfunctions develop, leading to severe consequences and even death.

The intensity of electromagnetic radiation is evaluated by The amount of energy falling per second on a perpendicularly placed area of 1 cm². The intensity of UHF radiation can be determined using instrumental and calculation methods via a formula or nomogram (Examples are provided in special manuals). The calculation method is used in preventive and routine sanitary supervision. Using a nomogram significantly speeds up calculations and helps avoid arithmetic errors.

The electromagnetic field (EMF) in the frequency range from 300 MHz to 300 GHz—which includes ultra-high frequencies (UHF) from 300 to 3000 MHz (decimeter waves from 1 to 0.1 m); super-high frequencies (SHF) from 3 to 30 GHz (centimeter waves from 10 to 1 cm); and extremely high frequencies (EHF) from 30 to 300 GHz (millimeter waves from 1 to 0.1 cm)—is evaluated by the power flux density (PFD). The unit of measurement for PFD is watts per square meter (W/m²) and its derivatives—0.1 mW/cm², 100 µW/cm², etc.

At PFD levels up to 7 mW/cm², neither local nor general heating is observed, so such intensity is classified as a sub-thermal or non-thermal level. PFD exceeding 7 mW/cm², which produces a thermal effect, is called thermal. Table 5.4 presents the minimum EMF intensity values at which a thermal effect is observed.

Class="center">Table 5.4 Threshold EMF intensities causing a thermal effect in body tissues due to radar radiation

In addition to thermal effects, non-thermal or specific effects of UHF and EHF fields are also distinguished, manifesting primarily upon repeated exposure to centimeter and decimeter waves at a PFD of about 1 mW/cm² (sub-thermal effect). The consequences of such exposure include dysfunctions of the central nervous system (CNS), Cardiovascular system (CVS), gastrointestinal tract, etc. Acute forms of injury are extremely rare; chronic injury symptoms are more common—dizziness, increased fatigue, light Sleep, memory impairment, headaches, general weakness, decreased sexual potency, Menstrual cycle irregularities, etc., indicating changes occurring in the CNS and CVS. Visual organ damage primarily manifests as cataracts. Such changes typically appear several months or years after starting work at a radar.

Prevention of the Adverse effects of UHF radiation

Measures against the adverse effects of UHF radiation are implemented during preventive sanitary supervision at the stage of radar design and the construction of facilities within their operational range to ensure compliance with established standards and regulations. Designers must provide shielding and tight sealing for all assemblies and units capable of emitting UHF fields and X-rays.

For individual protection, radar specialists use protective overalls and goggles. Overalls are made of special metallized fabric, while goggles are manufactured from metallized Glass or brass mesh. Protective equipment must be inspected semi-annually. Additionally, to protect health, the specialist's working time is reduced and, whenever possible, the duration of the station's operational emission is limited.

Inside the station cabin, an overheating microclimate is created due to the elevated air temperature heated by the surfaces of operating equipment. This causes strain on operators' thermoregulation processes, impairs conditioned reflex activity and analyzer functions, and reduces performance and work quality. Therefore, radar cabins are equipped with supply and exhaust ventilation. Optimal microclimatic conditions are provided by air conditioning. Thermal insulation of the station cabin helps reduce the radiation temperature. Furthermore, operating personnel must be provided with rational clothing.

To prevent visual fatigue, it is essential to establish clear standards for optimal workplace lighting that preserves dark adaptation, train operators in ergonomic screen-use practices, and ensure adequate dietary vitamin intake. Additional vitamin supplements are provided when necessary. Before reporting for duty, operators must get adequate rest, which is vital for maintaining performance quality at the display screen. Therefore, sleeping quarters must be free from noise, conversations, human movement, light Interference, and other distractions. During a six-hour shift, it is advisable to take a 10-minute break every 2 hours for active recovery, such as physical stretching or an outdoor jog.

When selecting a technical site (position), it is crucial to consider whether the allotted area is sufficient for placing the radio engineering facility, as well as its distance from residential and industrial buildings. To protect local residents from the effects of each radar system, sanitary-protection zones and building-restriction zones are established. A sanitary-protection zone is defined as an area where, at a height of up to 2 m above ground level, the maximum permissible levels (MPLs) of electromagnetic fields generated by the operating radar are exceeded. A building-restriction zone is defined as an area where MPLs are exceeded at a height of more than 2 m above ground level during radar operation. The outer boundary of this zone is determined relative to the maximum height of prospective buildings—specifically at the top-floor level where electromagnetic field levels do not exceed permissible limits during radar operation. These zones are established around or within the sector of the radar antenna (the microwave radiation source).

The dimensions of the zone and the safe duration of exposure depend on the radar's power, antenna gain, and maximum permissible radiation levels. The calculation of normal radiation zones is performed using a formula or a nomogram.

From a hygienic perspective, the operating modes of radar stations are of great importance, characterized by spatial intermittence, temporal intermittence, or both simultaneously.

Spatial intermittence of exposure is caused by the periodic movement of the antenna in space, primarily its circular motion. The antenna rotation speed typically ranges from 3 to 6 revolutions per minute, though it can be 3 to 5 times higher.

Temporal intermittence of exposure is due to the cyclic nature of radar signal emission. Radar operating times under various modes can range from several hours to a full day. For example, a meteorological radar operating on a cycle of 30 minutes of emission and 30 minutes of pause accumulates up to 12 hours of operation per day, whereas airport radars generally operate continuously around the clock. Structure/19.html">The Importance of accounting for these modes lies in the fact that their spatial and temporal variations are closely linked to both the magnitude of the maximum permissible level and the shape and size of the sanitary-protection zone. For instance, if emission is omnidirectional (circular), the sanitary-protection zone will surround the facility, although its shape may vary depending on the local terrain. If emission occurs only within a specific sector, establishing a sanitary-protection zone outside that sector is unnecessary.

If it is impossible to locate the radar antenna at a safe distance from inhabited buildings, the walls and windows facing the emitter must be shielded. As a natural shield, it is advisable to plant trees in a strip up to several tens of meters wide around the buildings.

Current sanitary supervision aims to maintain electromagnetic field levels within the residential zone within the limits established by DSanPiN 239-96. It is carried out by specialists from sanitary-epidemiological stations in accordance with plans approved by state sanitary doctors.

The unit medical officer oversees the compliance of radio engineering stations (radars and radio stations with a power of 1 kW or more) regarding the availability of:

- an order by the unit commander appointing a responsible person (from among engineering and technical staff) to monitor the Implementation of measures protecting personnel and the public from electromagnetic field exposure;

- a site layout plan for stations utilizing stationary and mobile radio engineering equipment, indicating:

a) the locations of emitting antennas and their operational sectors;

b) potential personnel positioning areas, specifying electromagnetic field values and permissible exposure times;

c) the boundaries and dimensions of the sanitary-protection zone and building-restriction zone around the unit's radio engineering stations, agreed upon with the operational medical service;

d) the locations of neighboring settlements and military housing estates situated within the building-restriction zone, along with electromagnetic field values on the upper floors of these buildings and structures;

- instructions on protecting personnel and the public from electromagnetic field effects generated by radio engineering stations, tailored to the specific conditions of the unit and detailing:

a) safe working practices and methods;

b) data on electromagnetic field levels at workplaces and potential personnel locations;

c) permissible exposure times for personnel in these areas;

d) Procedures for using personal protective equipment;

e) guidelines regarding prohibited radar emission sectors directed toward settlements and residential areas of the military base, alongside other required documentation:

- a logbook for recording electromagnetic field measurements maintained by the person appointed by the unit commander's order;

- a briefing log for service members authorized to work directly with the unit's radio engineering equipment (initial briefings before starting work and periodic briefings at least once every six months);

- a list of positions whose occupants are considered to be working with the unit's radio engineering equipment, approved by the unit commander's order.