译者序
按照欧美国家的电气火灾分类标准，静电引发的火灾属于电气火灾的范畴。静电往往发生在无形之中，在悄无声息中点燃可燃物，易造成群死群伤的事故。静电发生突然，发生机理复杂，最常见的火灾形式是静电电弧引燃易燃气体，通常现场留不下典型痕迹，只能从发生的可能性加以判断认定，静电发生的机理是什么呢，如何开展调查呢？本文重点介绍最新版的《火灾和爆炸调查指南》中第9章 电气及火灾中第12节静电火灾，更多详细内容请参考《关于静电的操作规程》。由于篇幅原因，此文分为上下两篇，上篇主要介绍常见引发静电的情况以及静电产生原理两部分，下篇将介绍引燃电弧、电弧引燃能量、静电积累的控制、静电引燃的必要条件以及雷击等相关内容。
图1 NFPA921
火灾与爆炸调查指南
-2017版
图2 NFPA77
关于静电的操作规程
-2014版
中国人民警察大学火灾物证鉴定中心
西安科技大学火灾物证鉴定中心
2019年09月08日
《火灾和爆炸调查指南》
--静电火灾
NFPA921
火灾和爆炸事故调查指南
9 electricity and fire
电气原理及电气火灾
9.12 static electricity
静电火灾
9.12.1 introduction to static electricity
静电概述
9.12.1.1Static electricity is the electrical charging of materials through physical contact and separation and the various effects that result from the positive and negative electrical charges formed by this process. Static electricity is accomplished by the transfer of electrons between bodies, one giving up electrons and becoming positively charged, and the other gaining electrons and becoming oppositely, but equally, negatively charged.
静电是通过物质的接触与分离而产生的放电现象，此过程中产生的正负电荷，具有多种作用方式。静电是通过物体间电子的转移造成的，一个物体失去电子，带正电，另一物体接受电子，带负电，但是电荷始终保持平衡。
图3NFPA77中绝缘材料相对位移静电产生示意图
9.12.1.2Common sources of static electricity include the following:
Pulverized materials passing through chutes or pneumatic conveyors
Steam, air, or gas flowing from any opening in a pipe or hose, when the stream is wet or when the air or gas stream contains particulate matter
Nonconductive power or conveyor belts in motion
Moving vehicles
Nonconductive liquids flowing through pipes or splashing, pouring, or falling
Movement of clothing layers against each other or contact of footwear with floors and floor coverings while walking。
Thunderstorms that produce violent air currents and temperature differences that move water, dust, and ice crystals, creating lightning
Motions of all sorts that involve changes in relative position of contacting surfaces, usually of dissimilar liquids or solids
产生静电的常见情况如下：
通过输送槽或气动输送机传导的粉状材料；
从管道或软管开口处流出的，含有水分或颗粒物的蒸汽、空气或可燃气体；
运动着的非导电的电动输送带；
行驶着的车辆；
管道中流动的、喷洒的、倾倒的、下坠的非导电液体；
衣物层与层之间的相互移动，或在行走过程中，鞋与地板或鞋与地板覆盖物的接触；
在雷暴天气中，空气中产生的激烈电流和巨大温差，造成的水、尘埃和冰晶的转移，产生的雷电现象；
接触面的相对位置发生变化，常指不同的液体或固体之间，所有类似的运动变化。
9.12.2 Generation of Static Electricity.
静电的产生
9.12.2.1 General. The generation of static electricity cannot be prevented absolutely, but this generation is of little consequence because the development of electrical charges may not in itself be a potential fire or explosion hazard. For there to be an ignition, there must be a discharge or sudden recombination of the separated positive and negative charges in the form of an electric arc in an ignitible atmosphere. When an electrical charge is present on the surface of a nonconducting body, where it is trapped or prevented from escaping, it is called static electricity. An electric charge on a conducting body that is in contact only with nonconductors is also prevented from escaping and is therefore nonmobile or static. In either case, the body is said to be charged. The charge may be either positive or negative .
概述。完全阻止静电的产生是无法实现的，但就电荷本身而言，可能不具有火灾或爆炸危险性，因此仅仅产生静电是不会造成危害后果。只有在可燃气氛中，存在正负的电荷分离或突然结合，并以电弧的形式出现，才能导致静电引燃。在非导电物体表面，电荷的流动受到限制，限制电荷流出，此物体表面出现的电荷，称之为静电。导电物体仅与非导体接触，导电物体上的电荷流动也将受到限制，因此电荷也会处于无法转移或静止状态。以上情况，均可视为物体带电。带电负载可能是正极，也可能是负极。9.12.2.2* Ignitible Liquids.Static is generated when liquids move in contact with other materials. This phenomenon commonly occurs in operations such as flowing through pipes, and in mixing, pouring, pumping, spraying, filtering, or agitating. Under certain conditions, particularly with liquid hydrocarbons, static may accumulate in the liquid. If the accumulation of charge is sufficient, a static arc may occur. If the arc occurs in the presence of a flammable vapor–air mixture, an ignition may result.可燃液体。当液体与其他物质流动接触时，将产生静电。这种现象通常发生在作业过程中，如：管道中流动、混合、倾倒、灌装、喷洒、过滤或摇晃。在特定的情况下，特别是碳氢化合物液体中，可能出现静电电荷的积累。如果电荷积累的足够多，将会产生静电电弧。如果电弧发生在易燃预混气体中，可能发生引燃现象。
图4NFPA77中管道中液体流出时静电产生原理图
9.12.2.2.1Filtering with some types of clay or microfilters substantially increases the ability to generate static charges. Tests and experience indicate that some filters of this type have the ability to generate charges 100 to 200 times higher than achieved without such filters.
用有些粘土进行过滤或使用微量过滤器过滤，将显著增加产生静电的可能性。经实验和实践说明，使用某些此类过滤器进行过滤比不使用产生静电的可能性增加100-200倍。
9.12.2.2.2The electrical conductivity of a liquid determines its ability to accumulate and hold a charge. Liquids with very low conductivity do not have enough free charges to accumulate a significant charge. Liquids with very high conductivity have enough charges, but the charges cannot accumulate to a significant degree. Consequently, the high-hazard liquids are those with intermediate conductivity . The units for conductivity are siemens per meter, abbreviated as S/m. A siemens is the reciprocal of the ohm.
液体的导电性决定着液体积累和持有电荷的能力。液体的导电能力差，没有充足的自由电荷，无法积累足量的电荷。液体的导电能力强，具有充足的自由电荷，但是电荷无法积累到一定程度。因此，高危险等级的液体是那些导电性适中的液体，导电能力的单位是西门子每米，缩写为S/m。西门子是欧姆的倒数。Table9.12.2.2.2 Common Liquids That Have Conductivity
表9.12.2.2.2 常见液体的导电性
9.12.2.3 Charges on the Surface of a Liquid.液体表面电荷If an electrically charged liquid is poured, pumped, or otherwise transferred into a tank or container, the unit charges of similar polarity within the liquid will be repelled from each other toward the outer surfaces of the liquid, including not only the surfaces in contact with the container walls but also the top surface adjacent to the air or vapor space, if any. It is the latter charge, often called the surface charge, that is of most concern in many situations. In most cases, the container is of metal, and hence electrically conductive.带电液体以倾倒、灌装或其他方式注入容器时，液体内极性相似的单位电荷将相互排斥，向液体的外表面移动。外表面不仅包括容器壁与液体的接触面，也包括液体与周围空气或气体空间的外表面。在液体与周围空气或气体空间产生的电荷，称为表面电荷，往往需要特别关注。由于金属具有导电性，多数情况下选用金属容器，防止容器壁与液体的接触面的电荷积累。9.12.2.3.1Even if the tank shell is grounded, the time for the charge to dissipate, known as relaxation time, may be as little as a few seconds up to several minutes. This relaxation time is dependent on the conductivity of the liquid and the rate and manner that the liquid is being introduced into the tank, therefore, the rate at which the electrostatic charge is being accumulated.即使容器的壳体接地，电荷驱散的时间可能要持续几秒至几分钟不等，称此时间为驰豫时间。弛豫时间取决于液体的导电能力，液体注入容器的速率和方式，这里的速率指静电电荷的累积速率。9.12.2.3.2If the electrical potential difference between any part of the liquid surface and the metal tank shell should become high enough, the air above the liquid may become ionized and an arc may discharge to the shell. However, an arc to the tank shell is less likely than an arc to some projection or to a conductive object lowered into the tank. These projections or objects are known as spark promoters. No bonding or grounding of the tank or container can remove this internal charge.液体表面任何部位与金属容器外壳之间的电势差足够高时，其上部的空气可能发生电离，并向外壳释放电弧。但是，空气电离向容器外壳释放电弧的可能性，要小于向某些抛射物或在容器内沉降的导电物体释放电弧的可能性。这些抛射物或导电物体称为电火花发生器。没有进行接地或跨接保护的容器内部可能发生电荷的转移。9.12.2.3.3If the tank or container is ungrounded, the charge can also be transmitted to the exterior of the tank and can arc to any grounded object brought into proximity to the now-charged tank external surface.如果容器未进行接地处理，电荷也可能转移至容器外部，将向靠近正在放电容器外壳表面的接地物体释放电弧。9.12.2.4* Switch Loading. Switch loading is a term used to describe a product being loaded into a tank or compartment that previously held a product of different vapor pressure and flash point. Switch loading can result in an ignition when a low vapor pressure/higher flash point product, such as fuel oil, is put into a cargo tank containing a flammable vapor from a previous cargo, such as gasoline. Discharge of the static normally developed during the filling can ignite the vapor air mixture remaining from the low flash point liquid.加载转变。加载转变是指将某种物质注入容器或空间中，因此导致其挥发性和闪点发生变化。当挥发性较低或高闪点物质，注入到之前存储易燃液体的液舱中，且液舱中仍然残留有此易燃液体蒸汽时，加载转变将导致火灾的发生。填充过程中，常引起静电放电，可能点燃残留的低闪点易燃液体蒸汽与空气的预混气体继而引发火灾。9.12.2.5 Spraying Operations. High-pressure spraying of ignitible liquids, such as in spray painting, can produce significant static electric charges on the surfaces being sprayed and the ungrounded spraying nozzle or gun.喷洒操作。高压喷洒可燃液体时，在喷撒表面和未接地的喷枪喷嘴处，可能产生一定强度的静电电荷。9.12.2.5.1If the material being sprayed can create an ignitible atmosphere, such as with paints utilizing flammable solvents, a static discharge can ignite the fuel–air mixture.如果喷洒的物质能提供可燃气氛，静电放电可能将可燃预混气体引燃。9.12.2.5.2In general, high-pressure airless spraying apparatus have a higher possibility for creating dangerous accumulations of static than low-pressure compressed air sprayers.通常来说，相较于低压压缩空气喷雾器，高压缺气喷雾设备产生静电积累危险的可能性更大。9.12.2.6 Gases.When flowing gas is contaminated with metallic oxides or scale particles, with dust, or with liquid droplets or spray, static electric accumulations may result. A stream of particle-containing gas directed against a conductive object will charge the object unless the object is grounded or bonded to the liquid discharge pipe. If the accumulation of charge is sufficient, a static arc may occur. If the arc occurs in the presence of an ignitible atmosphere, an ignition may result.气体。在流动的气体混入金属氧化物或颗粒物、粉尘、液滴或喷雾，可能造成静电积累。含有颗粒物的气体喷雾直接作用到物体时，如果该物体没有接地或未连接放电管道，将造成电荷积累。如果积累的电荷足够多，静电电弧就会发生。如果电弧发生在可燃气氛中，就可能发生引燃。9.12.2.7 Dusts and Fibers.Generation of a static charge can happen during handling and processing of dusts and fibers in industry. Dust dislodged from a surface or created by the pouring or agitation of dust-producing material, such as grain or pulverized material, can result in the accumulation of a static charge on any insulated conductive body with which it comes in contact. The minimum electrical energy required to ignite a dust cloud is typically in the range of 10 to 100 mJ. Thus, many dusts can ignite with less energy than might be expended by a static arc from machinery or the human body.粉尘和纤维。在工业生产的粉尘和纤维处理加工过程中，可能产生静电电荷。表面抛出粉尘，或倾倒、摇动过程中产生粉尘，都可能在其接触的绝缘导体上产生静电电荷积累。点燃粉尘的最小放电能量通常在10mJ-100mJ之间。因此，相较于机械加工或人体静电电弧产生能量，许多粉尘可以被比其更低能量的电弧点燃。9.12.2.8 Static Electric Discharge from the Human Body.Numerous incidents have resulted from static electric discharges from people. The human body can accumulate an electric charge. The potential is greater in dry atmospheres than in humid atmospheres . If a person is insulated from ground, that person can accumulate a significant charge by walking on an insulating surface, by touching a charged object, by brushing surfaces while wearing nonconductive clothing, or by momentarily touching a grounded object in the presence of charges in the environment. During normal activity, the potential of the human body can reach 10 kV to 15 kV, and the energy of a possible arc can reach 20 mJ to 30 mJ. By comparing these values to the minimum ignition energies of gases or vapors, the hazard is readily apparent.人体释放的静电。许多事故是人体释放的静电造成的。人体可能积累电荷。相较于潮湿环境，在干燥环境中更容易积累电荷。如果一个人与地面绝缘，他在绝缘表面上行走、触摸带电物体、穿衣时表面摩擦以及快速触摸周围带有电荷的接地物体，都可能积累大量的电荷。在正常活动期间，人体的电位可以达到10kV至15kV，释放的电弧能量可能达到20mJ至30mJ。通过与气体或蒸汽的最小点火能量比较，人体释放静电的危险性显而易见。9.12.2.9 Clothing.Outer garments can build up considerable static charges when layers of clothing are separated, moved away from the body, or removed entirely, particularly when of dissimilar fabrics. For some materials and/or low humidity conditions, an electrostatic charge may be accumulated. The use of synthetic fabrics and the removal of outer garments in ignitible atmospheres can become an ignition source.衣物。当衣服各层被分开，从身体脱下，或完全脱掉时，外层衣服将积聚大量静电电荷，特别衣服含有不同的织物纤维。对于某些材料或在低湿度条件下，可能产生静电电荷积聚。在可燃气氛中，合成织物的使用以及脱衣过程，都可能成为引火源。Table 9.12.2.8 Electrostatic Voltages Resulting fromTriboelectric Charging at Two Levels of Relative HumiditySituation
