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
Adverse effects of physical factors on the human body

Adverse EFFECTS OF ENVIRONMENTAL physical factors on The Human Body can be attributed to two main circumstances:

- exposure to extreme values of factors that are necessary Components of the living environment;

- exposure to specific environmental factors that are not obligatory companions of humans in The process of their evolution.

In the first case, one can speak of the maximum and minimum permissible levels of factors and the determination of their optimal values.

As for the second circumstance, the ideal scenario is the complete absence of such a factor (laser radiation, certain electromagnetic radiations, muzzle blast waves, etc.), while permissible, maximum permissible (or tolerable), and critical values are established as regulatory standards.

Among all the physical factors shaping the environmental conditions of military-technical equipment, the most negative impact on personnel is often caused by extreme microclimatic conditions, leading to overheating or overcooling of military specialists.

In the onset of body overheating, a leading role belongs to such a microclimatic component as exposure to high ambient temperatures. This results in an increase in rectal Temperature to 39 °C and above, which in most individuals unadapted to relatively high air temperatures can cause heat stroke. An increase in Brain temperature to 43 °C is unconditionally fatal to the human body.

The Skin covers are quite resistant to thermal effects (the lowest skin temperature at which Burns are observed is 44 °C). Exposure to low temperatures leads to general or local cooling. Since humans in the course of evolutionary development have not developed sufficiently effective thermoregulatory mechanisms to reduce heat loss, the capacity of the human body to maintain thermal balance under cold conditions is quite limited.

In the process of general cooling, three phases are usually distinguished. In The first phase—compensation—the defense mechanisms of Physical and Chemical thermoregulation are activated. Reduced heat loss and increased heat production ensure the maintenance of an adequate thermal state for a certain time. In the subsequent phase—decompression—due to the depletion of energy resources, the functioning level of the main systems (cardiovascular, nervous, respiratory, etc.) drops, and body temperature correspondingly decreases to 32–34 °C. Finally, upon transition to the concluding phase—depression—a drop in body temperature to 29–30 °C is observed, indicating the inhibition of all body processes and approaching death.

In military operations, the limit for specialists to perform work in cold conditions is often set by the local cooling of the distal extremities.

The limit of cold tolerance based on the tactile sensitivity of the fingers corresponds to a skin temperature of 6–8 °C. The chill syndrome occurs at a skin temperature of 5–10 °C, and frostbite develops when it drops to 0 °C. The occurrence of frostbite is facilitated by the combined effect of low temperature, wind, high air humidity, wearing tight and wet footwear and clothing, prolonged immobility, and deterioration of the body's general condition due to overwork, exhaustion, illness, etc. Depending on the combination of these conditions, it can be observed even at temperatures of +3–7 °C, an example of which is the well-known "trench FOOT."

Acoustic noise of varying duration and intensity negatively affects personnel inside military equipment objects. It disrupts the perception of essential signals (reports, commands, etc.), acts as an irritant, reduces combat readiness (performance), and impairs the Functions of the Auditory Analyzer. It has been established that low- and medium-frequency continuous noise around 100 dB causes a pronounced decrease in auditory analyzer functions. A 10-minute exposure to noise levels of 120 dB is accompanied by temporary Hearing loss; acoustic energy intensity exceeding 125 dB turns the skin into a receptor field, making it a secondary entry gateway for noise into the body, while the 130 dB level is the pain threshold.

To produce an equivalent effect on the body, the level of non-continuous impulse noise must be higher than that of continuous noise. When shortening the duration of noise periods in the total exposure to 25–30%, this difference will amount to 5 dBA. Impulse noise (at the same total power) has a more adverse effect on humans than stable noise. The Nature of Changes in the body resulting from impulse noise depends on the pulse repetition rate, rise time, and peak pressure level. The most significant is the specific impact of impulse noise on the Organ of Hearing. The critical peak impulse noise value that damages the tympanic membrane is 185 dB. At lower peak pressure values, functional and morphological changes in The Organ of hearing depend on pulse parameters, total duration, and periodicity of noise exposure. Impulse noise causes a decrease in auditory sensitivity due to prolonged vasospasm of the sound-receptive apparatus, leading to Metabolic Disorders within it and the subsequent development of hearing impairment.

The nonspecific effect of impulse noise manifests as the suppression of Central Nervous system (CNS) activity (increased fatigue, memory and Sleep disorders, inhibition of mental processes, etc.) and Cardiovascular system (CVS) activity (accelerated pulse, elevated Blood pressure, ECG changes), which affects combat and operational performance indicators. In particular, this impacts the results of firing various types of weapons.

When firing modern artillery systems equipped with muzzle brakes, the muzzle Shock wave exerts the most severe effect on personnel among the three generated waves (muzzle, ballistic, and explosion-induced shock waves). At a pressure of up to 0.15 kg/cm², no physiological shifts are detected. With a further increase in pressure, damage to the organ of hearing, a decrease in combat readiness (performance), and deterioration of well-being are possible, while The impact of maximum muzzle wave levels—for instance, when firing large-caliber guns, which is additionally accompanied by infrasound generation—causes severe pain.

Sharp drops in atmospheric pressure more selectively affect barosensitive Organs. For instance, in case of impaired baroaccommodation of the affected organs, such pressure differentials can cause barotrauma—mechanical injuries such as hemorrhages, ruptures, etc. Humans tolerate pressure increases at a rate of 40–45 mm Hg per 1 s quite easily. Pulmonary hemorrhages typically occur at a pressure differential of 0.5 kg/cm² per 1 s or more.

The action of general and local vibration causes functional and organic disorders primarily in the CNS and CVS. Changes in the CNS occur under METABOLISM/18.html">The Influence of powerful afferent impulses generated by general vibration in tens of thousands of body mechanoreceptors. Electroencephalography objectively registers a reliable decrease in amplitude, enhancement of the ß-rhythm, and suppression of the a-rhythm. Polyneuropathic syndrome develops. Due to the irradiation of excitation from the vibration centers of the Cerebral Cortex to adjacent areas, primarily the vasomotor center, changes occur in the functional state of peripheral vessels, while simultaneous excitation of pain and temperature sensitivity centers triggers The Development of diencephalic syndrome with neurocirculatory disorders. In addition, visual acuity decreases, vestibular functions are impaired, and the range of sound perception is reduced.

The most pronounced adverse effect on various physiological systems is observed under low-frequency vibration. A number of Internal Organs enter into Resonance with vibration at frequencies from 3 to 90 Hz, which is accompanied by severe subjective sensations without clearly localized pain points, headaches, abdominal and cardiac pain, and pain in the limb Muscles. Alongside this, pronounced hemodynamic disorders develop, and The activity of the CNS, visual analyzer, and Endocrine System deteriorates. Pain symptom complexes occur when the body is exposed to vibrations with the following characteristics:

- frequency 10 Hz, displacement amplitude 2.4 mm and above (vibration velocity level 130 dB);

- frequency 50 Hz, displacement amplitude 1.2 mm and above (vibration velocity level 137 dB);

- frequency 60–70 Hz, displacement amplitude 0.8 mm and above (vibration velocity level 137 dB).

Although such high levels of vibration parameters are not characteristic of military equipment operating in standard mode, they may occur during operation under extreme environmental conditions.

Significantly more pronounced effects on humans are exerted by impact accelerations, which typically occur when a combat vehicle is jolted by a gunshot. Under an impact load on the HEAD exceeding 5g, a person experiences a state of brief stupor, followed by a deterioration in the quality of performing military-professional duties.

It has been established that local impacts directed solely at the head are tolerated worse by humans than general impact loads applied to the entire body. The threshold of relative "safety" for the brain is an impact where the collision speed of the head against an obstacle does not exceed 2.5 m/s, whereas damage to the cranial bones of an unprotected head is observed at an impact velocity of 4.58 m/s.

General and local throwing effects resulting from the jarring of the support upon which the operator is seated—caused, for example, by a seismic shock wave—are also dangerous.

Extremely high impact accelerations with a duration of less than 1 ms each are practically imperceptible to the body, as this timeframe is too short to overcome the inertia of body mass. However, as the duration of exposure increases, so does the human body's physiological response to the impact pulse. Upon reaching 70 ms, biological fluids begin to react, while durations exceeding 100 ms trigger various reflex responses and alterations in Muscle tone. Even for a restrained individual, sudden Displacement of the limbs and head, or sharp impacts against surrounding surfaces and objects, can lead to incapacitation.

Even in the absence of a direct collision with an obstacle, excessive flexion or extension of the cervical spine caused by impact acceleration frequently results in concussion or acute cervical syndrome, which stems from the stretching of the neurovascular bundle in the neck region. For instance, if the support velocity reaches 3.5 m/s following an impact, the head's velocity will surge to 5 m/s with a displacement of 32 cm. The "whiplash effect" is most pronounced in unrestrained individuals, who are knocked down by impact accelerations when the support velocity ranges between 1.8 and 2.5 m/s.

Electromagnetic radiation in the microwave (SHF) range can adversely affect the health of personnel operating within the effective range of emitting devices and stations. At an SHF power flux density of 3–7 mW/cm², individuals exhibit distinct functional changes across multiple physiological systems (such as decreased hemodynamic parameters and prolonged sensorimotor reaction times), which are attributed to the non-thermal effects of microwaves. Higher radiation levels can provoke local and general hyperthermia, causing damage to specific organs (Gonads, the crystalline lens, and the gastric mucosa) as well as disorders in the nervous and cardiovascular systems. Nevertheless, to date, no specific pathology or characteristic symptom complex has been identified for SHF exposure, unlike radiation sickness caused by ionizing radiation.

When exposed to UHF and HF radiation, the most hygienically significant factors for equipment maintenance specialists are the components of the electromagnetic field—specifically, the electric (E) and magnetic (H) fields. Alterations in the functions of the central nervous system (CNS), cardiovascular system (CVS), and peripheral blood are observed in individuals systematically exposed to an electric field strength of approximately 1000 V/m and a magnetic field strength of 10 A/m.

Laser radiation triggers biological effects that induce primary changes in irradiated Tissues—such as the eyes and skin—along with secondary or non-specific systemic responses throughout the body. It poses an exceptional hazard to the visual system. Eye injuries can result from both direct exposure to a laser beam and reflections from surrounding surfaces or objects. The energy density threshold for injury depends on both the laser wavelength and its operating mode.

The biological impact of an electrostatic field (ESF) depends on various factors, including whether the person is grounded, the direction of the field lines, and the body's posture within the field.

Under natural conditions, living organisms exist within the Earth's ESF at a field strength of 0.13–0.15 kV/m. Complete isolation from this field leads to rapid mental fatigue during cognitive tasks. Conversely, exposure to high-strength ESFs (60 kV/m and above) is detrimental to the body's conductive systems, suppressing cardiovascular functions (hypotension, bradycardia) and central nervous system activity (diminishing work precision and increasing error rates).

Similar functional disruptions occur in operators exposed to magnetostatic fields (MSFs). Furthermore, exposure to MSF strengths ranging from 1×10⁵ to 5×10⁵ A/m often leads to Complaints of memory impairment, dizziness, and insomnia.

In military practice, personnel may be exposed to soft X-ray radiation. For instance, in various radar systems, vacuum electronic devices operating at anode voltages of 12–100 kV can serve as sources of such radiation. Due to its low energy and limited penetrating power, this radiation is primarily absorbed by the superficial layers of the body, resulting predominantly in skin injuries. The damaging effects of soft X-rays are exacerbated when combined with microwave radiation—a scenario that can occur if safety protocols are violated during radar repair and alignment.