Electrosecurity
One of the major problems by development, industrial release and operation of the electromedical equipment is maintenance of a full electrosecurity for the attendants and patients. The basic safety means from action on an organism of an electric current is protective ground connection. Defeat of an organism by an electric current can be in the form of an electric trauma or electric impact. Electric trauma is a result of external local action of a current on a body: electric burns, electrometallization of skin, signs on a current. Electric burns are consequence of thermal action of the current which is passing through a body of the person, or occur under action of the electric arch, arising usually at short circuits in installations with a pressure above 1000 V. Electrometallization of a skin occurs at introduction in a skin of the smallest particles of metal fused under action of the current. Electric signs on the current, leather being by defeat in the form of sharply outlined round spots arise in places of an input and an output of a current from a body at dense contact to parts of a body of the person being energized. Electric impact is excitation of tissues of an organism under action of a current, which is accompanied by involuntary convulsive reduction of muscles. Electric impacts can cause the heaviest damages, amazing internal bodies of the person: heart, lungs, the central nervous system, frustration of intimate activity (infringement of a rhythm, fibrillation of ventricals of hearts), frustration of breath, a shock, in especially heavy cases leading a fatal outcome. Action of an electric current on an organism depends on a plenty of various factors, basic of which are: the size of the current defined by a voltage enclosed to a body and resistance of a body, kind and frequency of a current, duration of influence, and way of passage of a current.
The size of a current is the basic parameter defining a degree of defeat. Sensations of a current frequency of 50-60 Hz appear at force of a current 1 мА at compression hands of electrodes, convulsions in hands begin at increase of a current till 5-10 mА, at a current 12-15 mА it is already difficult to come off electrodes. At 50-80 mА the paralysis of breath comes, and at 90-100 mА and duration of influence of 3 seconds and more - a paralysis of heart.
Electric resistance of a body is not a constant. On low frequencies it is defined, basically, resistance of a horn layer of a skin. At the intact dry skin its specific volumetric resistance makes nearby 10 Ohm∙m. At a damp skin its resistance can decrease in tens and hundreds times.
Time of action of a current for an organism has the major value for exception of accident. The way of a current to a body of the person is important. Cases of defeat at which the current passes through heart and lungs, i.e. by hand to a hand, or by hand to a leg are especially dangerous.
A current -
a charge proceeding through biological object in unit of time.
Resistance of a body of the person consists from resistance of
internal tissues, organs and resistance of skin. Resistance of
internal parts of an organism poorly depends on the general condition
of the person, in calculations
Resistance Rskin
of skin depends upon the internal and external reasons
(hyperhidrosis, humidity). Besides on different sites of bodies skin
has different thickness and various resistances. Therefore it in
calculation does not accept and consider
.
At work with the electronic medical equipment possible measures on a safety should be stipulated all.
The basic and the main requirement is to make inaccessible a contact of the parts of the equipment which are being energized.
For this purpose parts of devices and apparatuses are isolated from each other and from the frame of apparatuses. Isolation is called the basic or working. Apertures in the frame should exclude an opportunity of casual penetration and a contact of internal parts of the equipment fingers, metal subjects. But it does not provide full safety for two reasons:
First, at a contact the person of the frame of the equipment through a body of the person can pass some current named by a current of outflow.
Secondly, probably damage of working isolation (ageing, humidity of air) arises electric short circuit of internal parts of the equipment with the frame - « breakdown on the case », and an external part accessible to a contact (frame) will energized.
Cases of defeat are connected by an electric current with a contact of the metal parts which are being energized of a power line most often meet.
The voltage of a touch decreases approximately in so much time, in how many resistance of grounding is less than resistance of a body of the person. Resistance of the protective grounding applied at operation of the electromedical equipment, should not be more than 4 Ohm. Electromedical devices and devices have the working part connected to a current or concerning body of a patient (electrodes, radiators, and sensors). Electric energy is transferred to tissues of a body of the patient by means of a working part at application of therapeutic, surgical electromedical devices. Biopotentials are perceived by means of a working part at use of diagnostic electromedical devices. Presence of a working part connects of the patient with the equipment and in the raised danger of defeat by an electric current. The electric current is used for medical influence on an organism in some medical devices. Misuse of such devices is connected with an opportunity of overdoses.
The patient in many cases cannot react to action electric current. It can be paralyzed, be under a narcosis. The skin of the patient is processed by disinfectant and other solutions and loses the protective properties. Conditions of carrying out of diagnostic and medical procedures can be the most various, from a cabinet of medical establishment, up to premises. Various conditions of operation, impose additional requirements to an electrosecurity of the equipment.