划重点！带你学《化学品安全指南》(十)物理特性(中英双语)

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✍1.4 静电 Static Electricity

1.4.1 综述 General

静电是物体表面上的电荷聚集。物质通常具有相同数量的正负电荷，在电子方面是平衡的。当不同的物质接触时，这些电荷会流动，造成正电荷与负电荷数量上的不平衡。摩擦会增大这个过程。例如，当某种货物在管线内移动时。当环境无法使电荷保持平衡时，它们会聚集在导电性能低下的材料上(绝缘物)。

Static electricity is the build up of an electrical charge on the surface of objects. Materials are usually electrically balanced with an equal number of positive and negative charges. When two unlike materials are in contact with each other these charges can flow from one to the other creating an imbalance in the number of positive and negative charges. This process is amplified by friction, for example when a cargo moves through a pipeline. Static charges build up on poor electrical conducting materials (insulators) where the charge cannot come into balance with its surroundings.

当两种带有聚集电荷的物质被放置在一起时，带电的表面会平衡它们的能量。如果能量的差异足够巨大，就会有动能帮助电荷越过两种物质间的空间，引起火花。

When two materials with an accumulated static electrical charge are brought close together, the two charged surfaces will seek to equalise their potential. If the difference in potential is large enough there will be sufficient energy for the charge to jump the gap between the two materials and a spark will be generated.

1.4.2 液体中的电荷聚集和消除

Charge accumulation and relaxation in liquids

不同液体的导电性能也不一样。液体的导电性能用每米pico siemens (pS)来衡量。电荷不会在每米导电性高于10pS的液体中聚集。这样的液体被称为无聚集或导电性物质。最常见的此类物质就是水。水是良好的导电体。

The ability of different liquids to conduct electricity varies. The electrical conductivity of a liquid is measured in pico siemens (pS) per metre. Charge accumulation does not occur in liquids having conductivity well above 10 pS per metre. Such liquids are called non-accumulators or conductive materials, the most common being salt water which is a good conductor of electricity.

但是，在每米导电性低于10pS的液体中，电荷聚集是很明显的。低导电液体被称为电荷聚集或非导体。

However, at a conductivity of below 10 pS per metre, the accumulation of an electrical charge may be significant. Liquids of low conductivity are called static accumulators or non-conductive.

为安全起见，所有导电性低于50pS/米的液体均被认为是非导体。

For safety reasons, all liquids with a conductivity reading of less than per metre are considered to be non-conductive.

1.4.3 静电的产生

Generation of static

在化学品运输船上，以下操作可能会导致静电火花的产生。

The risk of generating static sparking can occur during the following operations on board a chemical carrier：

(1)装货和卸货 Loading and unloading

当液体在管路中流动时会产生静电。所产生电荷的数量取决于液体的导电能力。

An electrostatic charge is generated within the liquid as it flows through pipelines. The amount of charge generated will depend on the ability of the liquid to conduct electricity, a property known as its electrical conductivity.

(2)蒸舱 Steaming

在洗舱时向舱内注入蒸汽会引起静电在凝聚水滴中聚集。

Injecting steam into a cargo tank during tank cleaning can cause a build up of static within the condensed water droplets.

(3)除气 Gas freeing

强力空气除气设备会引起静电在设备本体聚集。

Forced air gas freeing devices can cause a static charge to build up on the body of the equipment.

(4)货舱清洗 Cargo tank cleaning

当水流通过洗舱机的喷嘴被高压喷出时，会产生静电。结果，货舱中的水雾会带电。静电也会聚集在洗舱机喷嘴上，除非机体接地。

A static charge will be produced when water is forced, under high pressure, through the nozzle of a tank cleaning machine. As a result, the water mist inside the cargo tanks may become charged. A charge can also build on the nozzle of the tank cleaning machine unless the machine is electrically grounded.

(5)取样/测量 Sampling/gauging

测深棒或取样设备在尚未深入货舱时可能已经聚有电荷。将此类设备深入或提出货舱可能会在绳上产生电荷放电。

TObjects such as ullage probes or sampling equipment may already contain an electrostatic charge prior to being lowered into a tank. Lowering and raising such equipment in and out of a cargo tank may also generate a static charge on the line.

(6)货物抑制剂 Cargo inhibitors

添加粉末状的抑制剂或其他类似的物质可能会产生电荷，特别是当采用自由洒落方式的时候。

Adding of substances such as powdered inhibitors and other similar material may generate a static charge especially if added by free falling the substance into the tank.

1.4.4 货物操作过程中产生静电

Static generation during cargo operations

在管线中流动的货物由于同管线的摩擦，可能会带电。在到达货舱后依然带电。因为货物同货舱结构之间的电位差变得平衡，货物中的静电会逐渐消失。这个过程被称为电荷消失。其速度同液体的导电性有关。

A liquid flowing into a cargo tank can be charged by friction within the loading pipeline and remain charged within the cargo tank. The static charge within the cargo will slowly dissipate as the difference in potential between the cargo and the tank structure equalises. This process is called charge relaxation and its speed depends upon the conductivity of the liquid.

如果货物中含有水滴，当因为重力的原因，水滴逐渐沉淀于舱底时，会产生摩擦(假设货物的比重小于水)。同样，如果货物内含有不可溶解的气体，在气泡上升至液体表面的过程中，货物会变得带电。在以上两种情况中，会产生垂直电流， 导致液体表面带有高压，也被称为表面电压。随着时间的推移，电荷将根据液体的导电性同货舱结构相平衡。

Should the cargo contain water droplets, friction occurs when these droplets settle by gravity through the liquid in the tank (assuming that the liquid has a density less than that of water). Similarly, if the liquid contains a non-dissolved gas, the liquid could become charged when the gas bubbles rise to the surface of the liquid in the tank. In both of the above cases a vertical electrical current is established and a high voltage may result at the surface of the liquid, which is known as a surface voltage. Over time, depending on the conductivity of the liquid, the charge will equalise with the tank structure as described above.

如果将液体自由倾倒入货舱内，也会产生静电，这是因为同空气摩擦的原因。液体的溅落导致更多的电荷产生。因倾倒液体而溅起的带电液膜，将会较液体更长时间带电，原因是泡沫的薄膜仅为电荷提供了极其狭窄的向货舱结构放电的通道。

A static charge can also be generated if the liquid is allowed to fall freely into a cargo tank (splash filling), where friction with the air through which the liquid falls adds a further charge to the liquid. Charged foam, generated when splash filling some liquids, will retain a charge for a much longer time than the bulk of the liquid, as the thin film of foam bubbles at the liquid interface only provides a very narrow path for charge relaxation to the tank structure.

1.4.5 洗舱时产生的静电

Static generation during tank cleaning

在使用热水，或洗舱剂，或注入蒸汽洗舱时，在舱内会生成带静电的雾气。

A statically charged mist is formed inside the cargo tank when washing, particularly with hot water or a cleaning medium or when injecting steam into the tank.

在洗舱机内部，喷嘴处，水柱沿线，水柱喷在货舱结构表面，都会产生摩擦。

Friction is also generated within the tank cleaning machines at the nozzle, along the water jet and on impact against the tank surfaces.

带电的水雾在空货舱中滞留的时间长于在装卸液体货物时产生静电的时间。消除水雾中静电需要的时间几乎等于水雾凝聚到货舱表面所需的时间。在水雾中会产生高压，以致在空气中产生火花。

Statically charged mists can remain inside empty cargo tanks for a far longer time than the static charges generated within a liquid product during the loading and discharging process. Relaxation of a static charge within the mist can only happen as fast as the time it takes for the mist to condense on to the tank surface. Such high voltages can be generated within these mists that sparks can occur even in air.

1.4.6 会产生静电的移动设备

Static generating portable equipment

当一个绝缘的或未接地的电极浸没在一个静电场内，就会带电。但无法导向大地。如果电势的能量足够大，就会在电极和舱壁或液体表面之间产生火花。如果周围气体可燃，就会被点着。能起到电极相同作用的甲板设备包括金属取样罐，移动泵， 以及量空挡和测深设备。用来降落这些设备的绳索也是潜在的静电生产者，特别是合成纤维制成的绳索。所以绝对不允许用合成纤维绳索将设备降落到货舱中。

When an insulated or unearthed electrode is immersed in an electrostatic field it becomes charged, but the charge has no path to earth. If the difference in electrical potential is large enough a spark can then jump from the electrode to the tank wall or to the surface of the liquid. If the atmosphere is flammable, ignition will occur. Examples of such equipment used on deck that may act as an electrode include metal sampling cans and portable pumps as well as ullaging and sounding equipment. The lines used to lower such equipment are also potential generators of static electricity, particularly ropes made of synthetic fibres. Ropes made of synthetic fibres should never be used to lower equipment into tanks.