Main causes of electric shock
The main causes of electric shock to a person are:
• electric shock when using faulty household electrical appliances;
• connection to non-insulated parts of an electrical installation (contacts, wires, clamps, etc.);
• erroneously supplied voltage to the workplace;
• the appearance of voltage on the body of equipment, which under normal conditions is not energized;
• electric shock from a faulty power line (approaching a faulty power line at an unacceptable distance);
Classification of electric shocks. Consequences of electric shock.
Electric shocks according to severity can be divided into several groups:
• electric shock without loss of consciousness, without disturbance of breathing and cardiac activity;
• electric shock, characterized by loss of consciousness, while breathing and heart activity are not impaired;
• electric shock, in which a person loses consciousness, in addition, breathing and heart activity are disrupted;
• electric shock;
• state of clinical death.
If a person has impaired cardiac activity and breathing, then it is necessary to immediately carry out resuscitation measures: artificial respiration (using one of the methods: mouth to nose or mouth to mouth) and direct cardiac massage.
Electrical shock may result in electric shock. Electric shock is a severe, reflex reaction of the human body to electric shock. In this case, the person suffering from an electric shock must be immediately taken to the nearest medical facility. The victim must be under constant supervision of medical personnel, since the state of shock can last from one hour to a day. After this time, recovery of the victim or biological death may occur.
Methods and means of protection against electric shock
To protect against electric shock when touching parts of electrical equipment that are not normally energized, but may become energized if the insulation is damaged or for other reasons, the following is used:
• insulating materials (rubber gloves, galoshes, mats...),
• grounding,
• zeroing,
• protective shutdown...
Insulating agents are usually used during the repair and maintenance of electrical installations and are not discussed in this manual.
Grounding
Grounding of any part of an electrical installation or other installation is the intentional electrical connection of this part with a grounding device (ground electrode).
This connection is made with a conductor called grounding.
The illustration below shows grounding: the computer case is connected to a ground electrode (rail):
The grounding conductor is connected to a grounding conductor that has a direct connection to the ground. If a phase is accidentally connected to the body of the electrical equipment, a short circuit will occur and the fuses will trip. Consequently, the electrical circuit will be de-energized and the danger of electric shock will disappear.
The illustration below shows what can happen when a phase is shorted to the housing, if there is neither grounding nor grounding.
Zeroing
Protective grounding of any part of an electrical installation or other installation is the intentional electrical connection of this part with a conductor, which is called a grounding or neutral protective conductor.
If a phase is accidentally connected to the body of the electrical equipment, a short circuit will occur and the fuses will trip. Consequently, in this case, the electrical circuit will be de-energized and the danger of electric shock will disappear.
Single-phase networks, made according to modern standards, are equipped with three-pin sockets, to which three conductors are connected:
• phase,
• zero,
• nullifying.
This grounding conductor is connected to the solidly grounded neutral point (neutral) of the transformer in alternating current networks and to the solidly grounded midpoint of the power supply source in three-wire DC networks.
In the illustration below, the computer case is connected to the ground contact of the socket:
Safety shutdown
Protective shutdown is a protection system that provides automatic shutdown by a high-speed device of all phases of an emergency section with a total shutdown time from the moment a single-phase fault occurs of no more than 0.2 s.
In other words, a protective shutdown resembles a fast-acting fuse that trips when there is a danger of electric shock.
58) Classification of premises according to electrical safety
The current rules for electrical installations (PUE) divide all premises into the following three classes:
I. Premises without increased danger: dry, with normal air temperature, with non-conductive floors.
II. Premises with increased danger: damp with relative air humidity (long-term) more than 75%; hot with air temperatures exceeding +30°C for a long time; with floors made of conductive materials; with a large amount of released conductive technological dust, settling on wires and penetrating into electrical installations; with the placement of electrical installations with metal cases connected to the ground, metal structures of buildings and technological equipment that allow simultaneous contact with them.
III. Particularly dangerous premises: particularly damp with relative humidity close to 100%, a chemically active environment, the simultaneous presence of two or more conditions characteristic of premises with increased danger.
One of the measures to ensure electrical safety in premises of classes II and III is the use of reduced voltage current.
As examples of dividing premises according to the degree of danger, the following can be cited: Class I includes office premises and laboratories with precision instruments, assembly shops of instrument factories, watch factories, etc.; to class II - unheated warehouse premises, staircases with conductive floors, etc.; Class III includes all workshops of machine-building plants: galvanic, battery, etc. These also include areas of work on the ground in the open air and under a canopy.
59) Providing first aid to a victim of electric current
If you witness that a person has come under voltage, first of all, you need to free the victim from the effects of electric current as quickly as possible, especially if the person is holding onto a bare wire with his hand and is not able to independently break contact with the electrical installation.
The severity of electric shock directly depends on the duration of the current's effect on the body. To do this, it is necessary to turn off the electrical installation using devices specially designed for this purpose (switches, circuit breakers, removing fuses).
If there is no possibility of quick shutdown, it is necessary, using available means, to create conditions for quickly shutting down the section of the electrical installation with the victim. This can be throwing at overhead lines, breaking cables or electrical wiring with an ax, removing fuses with a dry rag, etc.
The note!
1. When providing first aid in electrical installations up to 1000V, to separate the victim from live parts, it is allowed to use improvised means that do not conduct electricity (dry board, stick, rope). The victim may be pulled by his clothes.
2. In electrical installations above 1000V, to provide first aid to a victim, it is necessary to use protective equipment, use dielectric gloves and boots, using insulating rods.
In this case, you must follow the rules of your own safety; the person providing assistance must ensure that he himself does not come into contact with live parts.
2) assessment of the victim’s condition.
After the victim is released from the traumatic factor, it is necessary to assess his physical condition. When assessing the condition, you need to pay attention to the following main signs:
• — consciousness: normal, impaired (inhibited or excited), absent;
• — breathing: normal, impaired (wheezing), absent;
• — pulse (determined in the carotid arteries): normal (well determined), abnormal, absent.
3) determining the nature of the injury that poses the greatest threat to the life of the victim.
That is, if a person is unconscious and other characteristic injuries are also visually visible (broken arm, bleeding, etc.), then first of all it is necessary to begin measures to return the victim to consciousness.
4) carrying out the necessary measures to rescue the victim.
The absence or presence of consciousness is determined visually.
If the victim is unconscious, it is necessary to monitor his breathing; if breathing is impaired due to the recession of the tongue, it is necessary to move the lower jaw forward. They bring the victim back to consciousness by sniffing ammonia or splashing his face with cold water.
If the victim is in an unconscious state, his pulse cannot be detected and there is no breathing, it is necessary to begin restoring the vital functions of the body by performing artificial respiration and external cardiac massage.
Artificial respiration is carried out if the victim is not breathing on his own, or when breathing is infrequent and convulsive.
5) maintaining the victim’s vital functions until medical personnel arrive.
Even if the victim does not show any signs of life (breathing, pulse), he cannot be considered dead, but resuscitation measures must continue until qualified medical personnel arrive.
6) call medical personnel or independently organize transportation of the victim to a medical facility.
Analysis of the causes of industrial accidents due to electric shock
As an analysis of the circumstances and causes of accidents resulting from electric shock shows, in some organizations managers and specialists do not comply with electrical safety requirements and labor protection obligations. In addition, violations of labor and production discipline requirements were revealed on the part of the victims.
Meanwhile, only properly organized work in electrical installations, good knowledge of the safety requirements when working in them and strict application of them in one’s work often make it possible to preserve the health and sometimes even the lives of both the workers themselves and strangers who come across operating electrical installations.
It should be noted that violations of electrical safety requirements are of a recurring nature.
The most common cases of electric shock are due to workers’ failure to take organizational and technical measures to ensure the safety of work in electrical installations.
Situation 1
As a result of a short circuit on the cable insert between the bus sections of a 0.4 kV switchgear, an electric arc occurred, from which the chief power engineer of a private production unitary enterprise received thermal burns. The investigation established that the chief power engineer, showing gross negligence, carried out work on electrical installations without taking organizational and technical measures, without using electrical protection equipment.
Organizational events
Organizational measures to ensure the safety of work in electrical installations are:
– appointment of persons responsible for the safe performance of work;
– registration of work with a work order, order or list of works performed in the order of current operation;
– issuing permission to prepare a workplace and issuing permission to work;
– permission to work;
– supervision during work;
– registration of transfer to another workplace;
– registration of a break in work, completion of work.
Safe work performance
To ensure safe work in electrical installations with voltage relief, the following technical measures must be carried out in the specified order:
1) the necessary shutdowns have been made;
2) measures have been taken to prevent the supply of voltage to the place of work due to erroneous or spontaneous switching on of switching devices;
3) prohibiting posters are posted on manual drives and on remote control keys of switching devices;
4) checked that there is no voltage on live parts that must be grounded;
5) grounding is installed (grounding blades are included, and where they are absent, portable grounding connections are installed);
6) “Grounded” signposts are posted;
7) if necessary, workplaces and live parts remaining under voltage are fenced and safety posters are posted.
Depending on the specific conditions, live parts are fenced before or after applying grounding.
Situation 2
While performing work to connect a spotlight to illuminate a work site at a construction site, a construction department electrician was fatally injured.
The investigation showed that the electrician did not carry out technical measures to ensure work safety, namely: he did not make the necessary shutdowns and did not take the necessary measures to prevent the supply of voltage to the work site.
In addition, during a special investigation, the state energy supervision inspector discovered that electrical installations were connected to the power grid without a work order issued by the State Energy Supervision Authority.
For reference:
electrical installations of temporary power supply (construction sites, attractions, etc.) must be presented to the state energy inspector for inspection and issuance of a conclusion on the possibility (impossibility) of their commissioning.
For reference:
connection of the consumer's electrical installations to the electrical network is carried out along with the energy supplying organization after concluding a power supply contract in the manner established by the Electricity Supply Rules, approved by Resolution of the Council of Ministers of the Republic of Belarus dated October 17, 2011 No. 1394, only if there is an inspection report of electrical installations by a representative of the state energy supervision body with a positive conclusion on the possibility of commissioning electrical installations into operation.
Cases of electric shock are not uncommon in the republic, due to deficiencies in the operational maintenance of electrical installations, expressed in the lack of storage procedures and the issuance of keys to cell doors, switchboards and electrical installation assemblies. Due to these shortcomings in the operational maintenance of electrical installations, not only workers are injured, but also the population, incl. children. At the same time, the heads of organizations do not take proper measures to prevent penetration into cameras, cells of electrical installations and do not impose proper requirements to ensure control over the storage, issuance and return of keys.
Situation 3
The causes of one of the fatal accidents that occurred with an electrician of electrical networks were shortcomings in the operational maintenance of electrical installations, expressed in the absence of a procedure for storing and issuing keys to the doors of the chambers of 10 kV electrical installations.
Prompt service
Important!
The doors of electrical installation rooms, chambers, switchboards and assemblies, except those in which work is carried out, must be locked.
The procedure for storing and issuing keys to electrical installations above 1,000 V (rooms and chambers of indoor switchgear, switchgear, outdoor switchgear), as well as to distribution boards and assemblies up to 1,000 V, located outside electrical installations above 1,000 V, is determined by order or instruction of the employer.
For reference:
ZRU – closed switchgear.
For reference:
KRU – complete switchgear.
For reference:
Outdoor switchgear is an open switchgear.
For each electrical installation room there must be at least 2 sets of keys, one of which is a reserve one. The keys must be registered with permanent operational personnel. In electrical installations without permanent operating personnel, the keys may be registered with administrative and technical personnel.
Keys must be numbered, stored in locked boxes and issued against signature:
– workers who have the right to individual inspection – from all premises;
- when performing work according to the order or by order of the work performer (supervisor) - from the premises in which the work is performed.
The keys must be returned by the work manager (supervisor) daily upon completion of work, when inspecting electrical installations - after completion of the inspection.
In electrical installations without permanent operating personnel, keys must be returned no later than the next working day after inspection or complete completion of work.
The issuance and return of keys must be recorded in a special free-form journal or in an operational journal.
Systematic maintenance
Often, electrical installations become potential sources of industrial electrical injuries due to improper installation and lack of systematic maintenance. Particularly dangerous to others are incorrectly installed and carelessly operated electrical installations and wiring in high-risk areas, especially dangerous outdoor electrical installations. These violations are most typical for organizations in the construction industry performing construction and installation work, where the risk of electric shock is high.
Situation 4
While performing work on constructing a concrete blind area for a residential building under construction, a mason from the construction department was fatally injured. The mason approached the place of work under the balcony, where the electric cables ran, and, since they interfered with his work, he grabbed the uninsulated section of the cable with his hand, as a result of which he was exposed to electric current. Due to the lack of control over the condition of electrical installations at the construction site and the performance of electrical installation work by electrical personnel on the part of the construction department power engineer, when moving the step-down transformer, the cable connections were not insulated and they were laid to a height of less than 2.5 m.
Requirements for installation and location of wires and lamps
Important!
Places of connection and branching of conductors of wires and cables, as well as connecting and branch clamps, etc. must have insulation equivalent to the insulation of the cores of entire sections of these wires and cables.
The wiring of temporary electrical networks with a voltage of up to 1,000 V, used in the power supply of construction sites, must be carried out with insulated wires or cables on supports or structures designed for mechanical strength when laying wires and cables along them, at a height above ground level, flooring, not less than ( m):
– 2.5 – above workplaces;
– 3.5 – above the aisles;
– 6.0 – over driveways.
General lighting lamps for workplaces and passages with voltages of 127 and 220 V must be installed at a height of at least 2.5 m from the ground level, floor, or decking.
When the suspension height is less than 2.5 m, it is necessary to use lamps of a special design or use a voltage no higher than 25 V.
Power supply of lamps with voltage up to 25 V must be carried out from step-down transformers, machine converters, and batteries.
Situation 5
A similar incident occurred at the construction site “Major repairs of an access overpass.” A concrete worker died as a result of touching uninsulated live parts of an electrical cable connected to a grinding machine.
During the special investigation, it was established that the senior foreman did not ensure the maintenance of existing electrical installations by specially trained personnel, the implementation of technical measures to ensure the safety of work in electrical installations, and allowed the grinding machine to be connected to the power supply without a residual current device (RCD) and a plug connection with a protective grounding contact.
Requirements for sockets
Important!
Plug sockets with a rated current of up to 20 A, located outdoors, as well as similar plug sockets located indoors, but intended to power portable electrical equipment and hand tools used outdoors, must be protected by an RCD with an operating current of no more than 30 mA, or Each socket must be powered from an individual isolation transformer with a secondary winding voltage of no more than 25 V.
For reference:
RCD – residual current device.
Sockets and plugs used in networks with voltages up to 25 V must have a design different from the design of sockets and plugs with voltages over 25 V.
Situation 6
While en route to work past a plastering station on a construction site, an 18-year-old student came into contact with a metal section of fence leaning against the plastering station, which had a section of cable with damaged insulation. As a result, the student died from electric shock. He was accepted for a period of practical training as a plasterer in a construction organization.
During the investigation, it was established that, in violation of safety requirements, the general contractor for the construction of the facility and the subcontractor did not develop measures to ensure safe working conditions, mandatory for all organizations and individuals involved in construction, incl. measures to turn off electrical installations at the end of the working day and measures to prevent unauthorized persons from supplying voltage to electrical installations.
Requirements for organizing the safe performance of work by subcontractors
Important!
The general contractor or lessor is obliged, when performing work on construction sites with the involvement of subcontractors or tenants:
– develop together with them measures to ensure safe working conditions, mandatory for all organizations and individuals involved in construction;
– ensure the implementation of planned activities and coordination of the actions of subcontractors and tenants regarding the implementation of labor safety measures at the work sites assigned to them.
For reference:
VL – overhead line.
Situation 7
Ignorance by employees of the requirements of the Rules for the protection of electrical networks with voltages over 1,000 V led to a group accident that occurred with three electricians of a closed joint-stock company.
At the beginning of the working day, the foreman instructed a team of three electricians to disassemble a mobile prefabricated tower, located in a parking lot owned by an open joint-stock company and located in the security zone of a 110 kV overhead line, into its component sections and move them to the warehouse territory. Electrical installers decided to move the tower to the warehouse without disassembling it into sections. While moving the tower, they did not pay attention to the 110 kV overhead line located in the path of movement. When the metal structure of the tower approached the 110 kV overhead line and its rack further came into contact with the line wire, it became energized. As a result of exposure to short circuit current and electric arc, 2 electricians died, and a third received electrical burns.
The investigation showed that, in violation of labor safety requirements in construction, the foreman of a closed joint-stock company allowed work to dismantle an 8.4 m high tower in the security zone of an existing 110 kV overhead power line without issuing a permit specifying safe working conditions or obtaining written permission to carrying out work at the owner of the line and monitoring the execution of work. The deputy director for capital construction of an open joint-stock company and the foreman of a closed joint-stock company did not organize the execution of an admission certificate for work in the security zone of the 110 kV overhead line, which establishes organizational and technical measures to ensure the safety of work. The labor safety engineer of an open joint-stock company did not provide introductory training on labor protection to electricians involved in performing work on the territory of a third-party organization.
Issuance of an admission certificate and an admission order
Important!
Before starting work in conditions of industrial risk, it is necessary to identify zones that are dangerous to people, within which hazardous production factors, whether or not related to the nature of the work performed, constantly operate or may operate.
Before the start of construction and installation work on the territory of the organization, the customer and the general contractor with the participation of subcontractors and the administration of the operating organization are required to issue an approval certificate in the prescribed form. Responsibility for the implementation of the measures provided for in the approval certificate lies with the heads of construction organizations and the operating organization.
When performing work in security zones of structures or communications, a work permit is issued with written permission from the organization that owns this structure or communications.
The work permit is issued to the responsible performer of the work (foreman, foreman, foreman) by a person authorized by order of the head of the organization. Before being allowed to work, the person in charge of the work is obliged to familiarize workers with the measures for the safe performance of work and conduct targeted training, which will be recorded in the work permit. When performing work on the territory of an existing organization, the permit must be signed, in addition, by the relevant official of this organization.
The person who issued the permit is obliged to monitor the implementation of the measures provided for in it to ensure the safety of work.
Introductory training on labor protection is carried out with the following persons:
– when participating in the production process;
– involvement in work (provision of services) in the organization or on its territory;
– performing work (providing services) on the instructions of the organization (under an agreement concluded with the organization).
Induction training is also carried out with employees of other organizations, incl. business travelers, when they participate in the production process or perform work on the territory of the organization.
Situation 8
A similar accident occurred with employees of another organization.
On the instructions of the director, 4 workers moved a mobile collapsible tower using a forklift. Not paying attention to the fact that there was a 10 kV overhead line in the path of movement, they brought the tower an unacceptably close distance to the power line and came under voltage. Three workers were thrown back by the shock wave, and one died.
Electrical circuits
In a number of organizations, work in electrical installations is carried out without diagrams, from memory or according to outdated diagrams that do not correspond to the actual state of electrical installations. Changes made in the electrical circuits during operation are not promptly noted on the diagram after the operations are completed.
Situation 9
While performing work to connect the cable supplying the trailer to the distribution cabinet, an electrician from the construction department died.
It was established that on the eve of the accident, the chief engineer gave the electrician a task to change the electrical installation circuit. However, an approval order (order) indicating specific changes in the distribution cabinet layout was not issued. The modified circuit was not tested for compliance with safety requirements, as a result of which a power supply circuit was allowed into operation that did not provide for the possibility of relieving voltage using a disconnecting device. In addition, the cause of the accident was that the victim was heavily intoxicated.
Important!
All changes in electrical installations made during operation must be reflected in diagrams and drawings signed by the person responsible for electrical equipment, indicating the date of the changes.
Information about changes in electrical circuits must be brought to the attention of electrical personnel, for whom knowledge of these circuits is mandatory, and recorded in the order log or in the operational log.
Technical documentation
Electrical safety during the operation of electrical installations is directly dependent on the level of technical documentation. There are often cases when organizations lack technical documentation.
However, as practice shows, unsatisfactory maintenance of technical documentation and its absence directly or indirectly affect the occurrence of electrical injuries.
Therefore, one of the most important conditions for ensuring the proper level of condition of electrical installations and their safe maintenance is high-quality technical documentation, timely checked and supplemented, corresponding to the actual situation in the electrical industry.
Nina Pilipenko , electrical engineer
