A, accident characteristics and cause analysis
(A) the characteristics of electric shock accidents in the water environment
1, because the accident happened in the water environment, it is not easy for people to escape after getting an electric shock.
2. Generally, people do not directly contact electrical equipment and conductors, but get an electric shock through the conductive effect of water, which is not easy to detect and prevent in advance.
3. People who come to the rescue afterwards often think that there have been accidents such as drowning and fainting, and directly go into the water for first aid, which is easy to cause a second electric shock accident.
In fact, after the human body is shocked, the degree of injury is not directly related to the voltage, but depends on five aspects: the current passing through the human body, the duration of the current, the way the current passes through the human body, the human body condition and the frequency of the current.
Studies have proved that when the current passing through the human body reaches or exceeds the escape current (16 mA for men and 10 mA for women), the human body will not be able to get rid of the charged body by itself, and it will be extremely painful and unbearable. If the time is too long, you may be in a coma, suffocate, or even die. A current of 30 mA is dangerous. When the current passing through the human body reaches or exceeds 30 mA, it will cause irregular heartbeat, coma, high blood pressure and severe spasm in a few seconds to several minutes, which may cause abnormal heartbeat and lead to death. 50 mA is the lower limit of ventricular fibrillation current (or lethal current), that is, the minimum current that causes ventricular fibrillation through human body. When a current of 50 mA passes through human body 1s, ventricular fibrillation may occur and people may die.
According to ohm's law, it = u/Rb. Under the same voltage condition, in the environment where the skin is immersed in water, the smaller the resistance of the human body, the greater the current passing through the human body. In addition, after research, the frequency of 30 ~ 300 Hz alternating current is the most harmful interval to human body, and 50 Hz industrial frequency alternating current is just in this interval, so 50 Hz industrial frequency current is very harmful to human body. At the same time, because the electric shock current in water often passes through the whole body and flows through the heart, the electric shock accident is particularly serious in the water environment.
(2) Cause analysis of the accident
1, electric shock accident of electric water heater in toilet
Usually, there are three reasons for electric shock accidents of electric water heaters in toilets:
First, from the water heater itself. Long-term use of the electric heating tube in the water tank of the water heater will cause metal surface fatigue. When it reaches the limit, it will break, causing the heating wire to connect with water. The voltage of 220V directly passes through the water and flows through the human body, forming a path to the ground, and a large amount of current passes through the human body. When the current exceeds 50mA, it will cause permanent damage to the heart and even immediate death. The second is from the water supply pipeline, especially the old buildings built in the early stage. The water supply pipe is made of metal pipe. Renovation of old buildings, improper maintenance of ground wires or pipe networks, and frequent electrification of water pipes have also caused electric shock accidents in water intake of electric water heaters. Third, the ground wire itself is charged, and most of the water heaters themselves have good ground wires, so the elimination of leakage faults depends on good grounding. But if the ground wire is charged, the water heater will suffer and get an electric shock.
2. Electrical equipment leakage, electric shock and drowning accidents in water.
The electrical equipment used in rural electric shock accidents mainly includes submersible pump, water pump, fish pond oxygen pump and oxygen machine. The underwater lighting equipment in the city is mainly parks. Due to the quality problems or long-term use of these equipment, the equipment is corroded, the water seal condition of electrical parts is destroyed, and the insulation of electrical lines is destroyed. Most of these electrical equipment are not equipped with leakage protection devices or the installation is not standardized, which eventually leads to electric shock accidents. At the same time, because the human body can't act autonomously due to spasm after being electrocuted in water, the death probability is much higher than that of ordinary electric shock accidents.
3. The power cord fell into the water and caused an electric shock accident.
The main causes of electric shock accidents caused by power line falling into water are as follows: First, the tower support of power line does not meet the requirements of line erection specifications, which causes tower collapse and line falling into water in typhoon or other bad weather, which is more common in rural areas; Second, poor or damaged line insulation is mostly caused by private connection and random connection when electricity is used in construction sites or rural areas; Third, when the sudden flood or the water level in the pit and basement exceeds the normal state, some normal electrical equipment, electrical lines and sockets are submerged, resulting in leakage.
Second, preventive measures.
To prevent the above-mentioned electric shock accidents in water environment, the key is to do effective prevention work from both technical and management aspects.
(1) technical measures
In terms of electricity safety technology, insulation, safe spacing, leakage protection, safe voltage, fence and fence are all protective measures to prevent direct electric shock; Protective grounding and protective zero connection are the most basic measures in indirect electric shock protection measures. The so-called indirect electric shock protection measures refer to the technical measures to prevent all parts of the human body from contacting the metal parts of electrical appliances that are not charged under normal circumstances but charged under fault conditions. Limited by space, this paper mainly expounds the correct selection of leakage protection devices for electrical equipment in water environment.
Functionally, leakage protection (residual current protection) device is mainly used to prevent indirect contact electric shock and direct contact electric shock, as well as to prevent leakage fire and monitor grounding fault. Commonly used leakage protection devices take leakage current or electric shock current as action signals. The processed action signal drives the actuator to act, so that the line can be quickly disconnected.
The working currents of current-type leakage protection devices are divided into 0.006, 0.0 1, 0.0 15, 0.03, 0.05, 0.075, 0. 1, 0.2, 0.3, 0.5, 1, 3, 3. 1000mA or more is low sensitivity, which is used to prevent leakage fire and monitor ground fault. In order to avoid misoperation, the rated non-action current of the protection device should not be lower than 1/2 of the rated action current.
According to the specification requirements, I-type mobile electrical equipment and hand-held power tools with metal shells, electrical equipment installed in harsh places such as damp or strong corrosion, construction electrical equipment in construction sites, temporary electrical equipment, and plug-ins in hotel rooms.
Water lighting equipment in sockets, swimming pools or baths in civil buildings with high risk of electric shock. Power supply lines and electrical equipment installed in water should be equipped with leakage protection devices.
Many factors should be considered when selecting leakage protection devices. In bathrooms, swimming pools, tunnels and other places with high risk of electric shock, high-sensitivity leakage protection devices should be selected. According to IEC4.79 (Effect of current passing through human body), when the alternating current passing through human body is less than 30mA, human body will not die due to ventricular fibrillation, which is not directly related to human humidity and contact voltage. Therefore, according to the international electrotechnical standard, leakage protection devices with working current not more than 30mA are used in all provisions to prevent personal electric shock. Therefore, in the hospital operating room, bathroom and other places with high risk of electric shock, leakage protection devices with action current of 30mA can be installed to prevent personal electric shock.
Some highly sensitive leakage protection devices (such as 10mA) are used in construction sites, homes and rural areas. In fact, the leakage protection devices of 10mA and 30mA have the same effect in preventing electric shock, and both can prevent people from dying of ventricular fibrillation. Because 10mA leakage protection device is expensive, it is not suitable for wide use, and its rated non-working current is only 5mA. Because rural low-voltage power grid equipment is often in outdoor and humid places, the normal leakage current is large, which is easy to cause misoperation. The consequence of frequent misoperation and power failure is often that the leakage protector is short-circuited or cut off, which makes the line lose the protection of grounding fault and leads to dangerous consequences.
Leakage protection devices in operation should be inspected and tested regularly. All parts, upper parts and terminals of the protector shell shall be kept clean and intact; Bakelite shell should not be deformed or discolored; There should be no cracks and burn marks; The name (or trademark), model, rated voltage, rated current and rated working current of the manufacturer shall be clearly marked, and shall meet the conditions and requirements of the operation line. The protection level of the protector shell should be adapted to the environmental conditions of the place of use. The terminal should not be loose; Connecting parts shall not change color. There should be no obvious corrosion on the terminals. There should be no noise when the protector works. The operating handle of the leakage protection switch should be flexible and reliable, and its reliability should be tested regularly with the test button during use.
(2) Management measures
In addition to the corresponding technical measures, the management of water environment electricity consumption is also essential. According to the common types of electric shock, it is suggested to take the following management measures and master the necessary preventive knowledge.
1, government departments and electric power management departments should strengthen supervision, strengthen electricity use guidance, and standardize citizens' electricity use. In order to strengthen the safety management of rural power supply and distribution lines, electrical equipment near ponds and reservoirs should be equipped with qualified leakage protection devices and necessary insulation measures. Put an end to private connection and random connection of lines. Do a good job in the management of the "three-line intersection" line.
2. Professional electricians must complete the power outage, electricity inspection, grounding wire installation, sign board installation and fence installation before starting the operation.
3. Suitable for activities in places with water, such as lakes, outdoor swimming pools and park waters. Pay attention to whether there are power supply lines, production plants and the distance between lines and electrical equipment and the water surface nearby to avoid easy water inflow. Especially in thunderstorm weather, don't swim in the open air.
4. Don't touch the trees near the wires. In some places, trees and wires are parallel. As the trees grow taller every year, some crowns surround the wires. When encountering thunderstorm and strong wind, trees and wires collide and rub with each other, which will lead to short circuit and discharge.
5. Don't shelter from the rain under overhead transformers and power line towers.
6. After the rainstorm, water is likely to accumulate on the roads in some places. At this time, it is best not to drown. If you have to wade, you must always observe whether there are any broken wires in the stagnant water near the road you pass. When you find the supply line falling into the water, don't handle it yourself. Mark the surrounding area immediately, remind other pedestrians not to approach, and notify the power supply department in time for emergency treatment.
7. If you are a non-professional, you must be cautious when buying second-hand electrical appliances and fully consider their safety performance.
8. It is very necessary to strengthen the publicity of electricity safety knowledge and electric shock first aid knowledge. If you knew the knowledge of electric shock first aid, many tragedies might not have happened.