The harm of human body static electricity and its countermeasures
1. Electric shock
In places where the humidity is lower than 40% RH, the human body is more likely to be charged. Normally, the human body is charged 2 to 5kV. The discharge voltage that makes the human body feel electric shock is about 2~2.5kV. When an electric shock occurs, most people will think whether there is a problem with the grounding or the building (structure) is not grounded. This is a more layman's idea, because a charged human body will discharge and produce no matter whether it touches the grounded or ungrounded (isolated) conductor. electric shock.
Suggested measures:
(1) Humidification, at least 50%RH;
(2) Use ion wind to eliminate human body static electricity;
(3) Spray static conductive coating or cover static conductive material on the surface of easy-to-touch conductors;
(4) Carpet with conductive fiber material.
2. Electronic equipment
Ordinary electronic devices withstand the human body electrostatic discharge potential value:
Withstand value of sensitive components: <1kV
Withstand value of MOS device with protection circuit: 1～4kV
Requirements of foreign computer rooms to limit static electricity on the human body:
Surface charge density of clothes and fabrics: <3μC/m2
Resistivity of dielectric material: <109～1010Ω·cm
Decay time of dielectric material: <1s
Work clothes power: <0.5μC/piece of human body* high potential: <1kV
Suggested measures:
(1) Laying static conductive floor/plastic board
Recommended value of Japan "Static Safety Guide": 103～106Ω
Recommended value of national standard GB50174-93: volume resistivity 107～1010Ω·m, surface resistance 105～108Ω
(2) Wear anti-static work shoes and clothing.
(3) Wear a grounded anti-static wrist strap.
(4) Install human body static elimination equipment that can prevent electric shock.
3. Human body static electricity in petrochemical sites
In petrochemical dangerous places, static electricity on the human body is one of the most dangerous hidden dangers. The reason is that there are many opportunities for the gas release source and the human body to be charged and discharged in the enterprise; the second is that most of the operators do not understand the danger of human body static electricity and the specific measures to prevent electrostatic discharge. Almost all domestic and foreign static electricity regulations put forward regulations to prevent human body static electricity, but unfortunately, most of these regulations lack operability in terms of dangerous limits and specific restrictions, so accidents occur in enterprises from time to time. For example, in 1972, a railway loading flash and fire accident of a certain factory of Fushun Petroleum, 1979 a flash and explosion fire accident in a grinding workshop of a Xi'an factory using gasoline to wipe the floor, a flash explosion and a fire accident of a car in Yanshan in 1983, and a small body in Tianjin in 1988 under the PP The flash explosion accident of material packaging, the sampling accident of Yongping Mine in 2000, the car refueling accident at the gas station, the flash explosion accident of pouring powder into the container, the flash explosion accident of sampling with small iron barrels, etc., all of these accidents directly threaten human life and property Security. The following discusses the physical characteristics of the human body itself.
Human body capacitance 100～400PF (a few can reach 1000PF), charged 2～5kV human body energy storage 0.4～2.5mJ (W=CV2/2, human body capacitance is calculated at 200PF); human body surface resistance 500～5000Ω, experimentally proved, simulated human body The instantaneous (about tens of ns) discharge energy transfer to the grounded metal body is as high as 80% to 100%, which is enough to ignite flammable and explosive gases, oil and gas, etc. (such as H2*small ignition energy less than 0.1mJ, gasoline vapor minimum ignition energy 0.26 mJ). Therefore, in petrochemical companies, there are more fire and explosion accidents caused by static electricity on the human body. Japan's "Electrostatic Safety Guidelines" has classified the human body as an isolated conductor for management, with a management index of 100V.
Suggested measures:
The countermeasures to prevent human body static electricity accidents (including anti-charge countermeasures and anti-discharge countermeasures) focus on the monitoring and behavior preparation of equipment and supplies in non-explosion-proof areas; anti-charge operations and anti-discharge operations should be considered in explosion-proof work areas. The specific recommendations are as follows:
Non-explosion-proof area:
①Detection of anti-static work supplies
②Maintenance of grounding electrode and grounding terminal
③Human body static discharge rod (metal), ion wind static eliminator
Explosion-proof area:
①Anti-static ground
②Local humidification
③Anti-static work supplies
④Anti-static work clothes and shoes
⑤ It is strictly prohibited to serve
⑥Equipment and tool grounding
⑦Do not touch the charged medium
⑧Intrinsically safe human body static elimination equipment, such as intrinsically safe human body static elimination, intrinsically safe static elimination sign (United States)
Control indicators of intrinsically safe human body static elimination equipment:
The discharge charge transfer amount is less than 0.1μC, the transfer energy is μJ level, the residual voltage of the human body after touch is less than 100V, and the residual energy is less than 0.1mJ.
Notice:
Individual specifications propose to install grounded stainless steel pipes on the escalators of the trestle to discharge the static electricity of the human body. The practice is improper. Considering the explosion-proof dangerous place, it is actually to add a dangerous point (ignition source). It is recommended to consider replacing the intrinsic safety in the design. Type product.