✍1.4 靜電 Static Electricity
1.4.1 綜述 General
靜電是物體表面上的電荷聚集。物質通常具有相同數量的正負電荷，在電子方面是平衡的。當不同的物質接觸時，這些電荷會流動，造成正電荷與負電荷數量上的不平衡。摩擦會增大這個過程。例如，當某種貨物在管線内移動時。當環境無法使電荷保持平衡時，它們會聚集在導電性能低下的材料上(絕緣物)。
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.
當兩種帶有聚集電荷的物質被放置在一起時，帶電的表面會平衡它們的能量。如果能量的差異足夠巨大，就會有動能幫助電荷越過兩種物質間的空間，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 液體中的電荷聚集和消除
Charge accumulation and relaxation in liquids
不同液體的導電性能也不一樣。液體的導電性能用每米pico siemens (pS)來衡量。電荷不會在每米導電性高于10pS的液體中聚集。這樣的液體被稱為無聚集或導電性物質。最常見的此類物質就是水。水是良好的導電體。
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，在每米導電性低于10pS的液體中，電荷聚集是很明顯的。低導電液體被稱為電荷聚集或非導體。
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.
為安全起見，所有導電性低于50pS/米的液體均被認為是非導體。
For safety reasons, all liquids with a conductivity reading of less than per metre are considered to be non-conductive.
1.4.3 靜電的産生
Generation of static
在化學品運輸船上，以下操作可能會導緻靜電火花的産生。
The risk of generating static sparking can occur during the following operations on board a chemical carrier：
(1)裝貨和卸貨 Loading and unloading
當液體在管路中流動時會産生靜電。所産生電荷的數量取決于液體的導電能力。
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)蒸艙 Steaming
在洗艙時向艙内注入蒸汽會引起靜電在凝聚水滴中聚集。
Injecting steam into a cargo tank during tank cleaning can cause a build up of static within the condensed water droplets.
(3)除氣 Gas freeing
強力空氣除氣裝置會引起靜電在裝置本體聚集。
Forced air gas freeing devices can cause a static charge to build up on the body of the equipment.
(4)貨艙清洗 Cargo tank cleaning
當水流通過洗艙機的噴嘴被高壓噴出時，會産生靜電。結果，貨艙中的水霧會帶電。靜電也會聚集在洗艙機噴嘴上，除非機體接地。
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)取樣/測量 Sampling/gauging
測深棒或取樣裝置在尚未深入貨艙時可能已經聚有電荷。将此類裝置深入或提出貨艙可能會在繩上産生電荷放電。
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)貨物抑制劑 Cargo inhibitors
添加粉末狀的抑制劑或其他類似的物質可能會産生電荷，特别是當采用自由灑落方式的時候。
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 貨物操作過程中産生靜電
Static generation during cargo operations
在管線中流動的貨物由于同管線的摩擦，可能會帶電。在到達貨艙後依然帶電。因為貨物同貨艙結構之間的電位差變得平衡，貨物中的靜電會逐漸消失。這個過程被稱為電荷消失。其速度同液體的導電性有關。
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.
如果貨物中含有水滴，當因為重力的原因，水滴逐漸沉澱于艙底時，會産生摩擦(假設貨物的比重小于水)。同樣，如果貨物内含有不可溶解的氣體，在氣泡上升至液體表面的過程中，貨物會變得帶電。在以上兩種情況中，會産生垂直電流， 導緻液體表面帶有高壓，也被稱為表面電壓。随着時間的推移，電荷将根據液體的導電性同貨艙結構相平衡。
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.
如果将液體自由傾倒入貨艙内，也會産生靜電，這是因為同空氣摩擦的原因。液體的濺落導緻更多的電荷産生。因傾倒液體而濺起的帶電液膜，将會較液體更長時間帶電，原因是泡沫的薄膜僅為電荷提供了極其狹窄的向貨艙結構放電的通道。
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 洗艙時産生的靜電
Static generation during tank cleaning
在使用熱水，或洗艙劑，或注入蒸汽洗艙時，在艙内會生成帶靜電的霧氣。
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.
在洗艙機内部，噴嘴處，水柱沿線，水柱噴在貨艙結構表面，都會産生摩擦。
Friction is also generated within the tank cleaning machines at the nozzle, along the water jet and on impact against the tank surfaces.
帶電的水霧在空貨艙中滞留的時間長于在裝卸液體貨物時産生靜電的時間。消除水霧中靜電需要的時間幾乎等于水霧凝聚到貨艙表面所需的時間。在水霧中會産生高壓，以緻在空氣中産生火花。
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 會産生靜電的移動裝置
Static generating portable equipment
當一個絕緣的或未接地的電極浸沒在一個靜電場内，就會帶電。但無法導向大地。如果電勢的能量足夠大，就會在電極和艙壁或液體表面之間産生火花。如果周圍氣體可燃，就會被點着。能起到電極相同作用的甲闆裝置包括金屬取樣罐，移動泵， 以及量空擋和測深裝置。用來降落這些裝置的繩索也是潛在的靜電生産者，特别是合成纖維制成的繩索。是以絕對不允許用合成纖維繩索将裝置降落到貨艙中。
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.