Electricity static

Static electricity (static for short) has been blamed for many fires and explosions, sometimes con ectly. Sometimes, however, investigators have failed to find any other source of ignition. So they assume that it must have been static even though they are unable to show precisely how a static charge could have been formed and discharged. 

A static charge is formed whenever two surfaces are in relative motion, for example, when a liquid flows past the walls of a pipeline, when liquid droplets or solid particles move through the air, or when someone walks, gets up from a seat, or removes an article of clothing. One charge is formed on one surface—for example, the pipe wall—and an equal and opposite charge is formed on the other surface—for example, the liquid flowing past it. 

Even if a static spark ignites a mixture of flammable vapor and air, it is not really correct to say that static electricity caused the fire or explosion. The real cause was the leak or whatever event led to the formation of a flammable mixture. Once flammable mixtures are formed, experience shows that sources of ignition are likely to turn up. The deliberate formation of flammable mixtures should never be allowed except when the risk 

Static electricity discharges and unexpected electrical currents are frequently overlooked as potential sources of ignition that must be controlled. Some of the conditions that may result in sufficiently intense electrical discharges or arcing are  

A program to ensure that a well-designed and effective electrical earth-grounding system and equipment bonding system is in place is an essential first step in 

Although static discharges are small electrical phenomena, they are significandy different from a high voltage electrical discharge to ground from a power system or 

Applied Process Design for Chemical and Petrochemical Plants 

The use of intrinsically safe electrical and instrumentation equipment in appropriately designed environments can guard against many electrically related discharges. Reference should be made to authoritative books on this subject. 

When two objects/particles separate after being in contact (equal charges), one particle loses electrons and becomes positively charged while the other gains electrons and becomes negatively charged. 

In storage or process tanks, a charge generation can occur if a liquid enters above Lhe liquid surface by the spraying or splashing of the liquid and a charged mist may form [64] and the bulk liquid will become charged. 

A common ignition source within chemical plants is sparks resulting from static charge buildup and sudden discharge. Static electricity is perhaps the most elusive of ignition sources. Despite considerable efforts, serious explosions and tires caused by static ignition continue to plague the chemical process industry. 

Flammable liquids are considered particularly static-prone if their electrical conductivity is within the range of 0.1 to 10 pS/m. If no particulates or immiscible liquids are present, these liquids are considered safe when their conductivity has been raised to 50 pS/m or higher. Blending operations or other two-phase mixing may cause such a high rate of charging that a conductivity of at least 1000 pS/m is needed for safe charge dissipation (British Standard 5958, part 1, Control of Undesirable Static Electricity, para. 8, 1991). 

Electrostatic Discharges An electrostatic discharge takes place when a gas- or a vapor-air mixture is stressed electrically to its break- 

Spark discharges are most common between solid conductors, although one electrode may be a conductive liquid or the human body. They appear as a narrow, luminous channel and carry a large peak current for a few microseconds or less. Sparks are the only form of discharge for which a maximum energy can be calculated, by using the expression 

C = capacitance of charged system, F V = initial potential difference between electrodes, V 

Surface charge densities cannot exceed the theoretical value of 2.7 X 10 5 C/m2, set by air breakdown, and are normally less than 1.5 x 1CT5 C/m2. 

When two dissimilar bodies or substances meet, electrons pass from one to the other at the surface contact area. When the bodies separate, particularly if they are of an insulating material, a difference of potential occurs 

1 All pipework and containers used for conve)dng flammable liquids should be effectively bonded together and earthed so that any static electricity produced is immediately discharged to earth before it builds up to a dangerous energy level. 

2 Workshop atmospheres where flammable solvenfs are used for spreading as in, say, material proofing processing, can be artificially humidified. Where practicable, specialised radioactive static eliminators or earthed metal combs near the charged material etc. can also be used. It is also a wise precaution to ensure adequate ventilation such as to keep the gas/air mixture well below the lower explosive limit (LEL) of fhe flammable solvent concerned. 

4 Certain processes, such as electrostatic paint spraying, make use of the characteristics of static electricity and special precautions against solvent ignition are required 

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An fuel-air mixture explosion can be initiated by a sudden discharge of static electricity. Yet, while flowing in systems, a fluid develops an electrical charge which will take as long to dissipate as the fluid is a poor conductor. The natural electrical conductivity of jet fuel is very low, on the order of a few picosiemens per meter, and it decreases further at low temperature. 

While with-in the mobile x-ray system, the waste in the sampler, is contained within a replaceable (and disposable) polyvinyl chloride (PVC) sleeve with a wall thickness of approximately 0.2-inches and a sealed bottom. It was anticipated that the PVC tube or sleeve would, with use, become highly contaminated with waste residues which drip of fall-off the sampler. The sleeve is coated with a conductive coating to prevent static electricity buildup . There are no sources of ignition in this sealed spare. The sampler (and waste) is coupling which includes a positive pressure gasket. This barrier is further isolated by a second barrier consisting of an epoxy coated aluminum sleeve also sealed-off from the main x-ray cabinet and PVC sleeve. There are also no potential sources of ignition in this isolated secondary space as well. 

As we have discussed earlier in the context of surfaces and interfaces, the breaking of the inversion synnnetry strongly alters the SFIG from a centrosynnnetric medium. Surfaces and interfaces are not the only means of breaking the inversion synnnetry of a centrosynnnetric material. Another important perturbation is diat induced by (static) electric fields. Such electric fields may be applied externally or may arise internally from a depletion layer at the interface of a semiconductor or from a double-charge layer at the interface of a liquid. 

Two states /a and /b that are eigenfunctions of a Hamiltonian Hq in the absence of some external perturbation (e.g., electromagnetic field or static electric field or potential due to surrounding ligands) can be "coupled" by the perturbation V only if the symmetries of V and of the two wavefunctions obey a so-called selection rule. In particular, only if the coupling integral (see Appendix D which deals with time independent perturbation theory)... 

Statexan ITA Static control agents Static decay Static decay times Static dissipation Static drying Static electricity Static eliminating devices Static mixers Static phenomena... 

Control of relative humidity is needed to maintain the strength, pHabiUty, and moisture regain of hygroscopic materials such as textiles and paper. Humidity control may also be required in some appHcations to reduce the effect of static electricity. Temperature and/or relative humidity may also have to be controlled in order to regulate the rate of chemical or biochemical reactions, such as the drying of varnishes, the appHcation of sugar coatings, the preparation of synthetic fibers and other chemical compounds, or the fermentation of yeast. 

Dry nitrocellulose, which bums rapidly and furiously, may detonate if present in large quantities or if confined. Nitrocellulose is a dangerous material to handle in the dry state because of sensitivity to friction, static electricity, impact, and heat. Nitrocellulose is always shipped wet with water or alcohol. The higher the nitrogen content the more sensitive it tends to be. Even nitrocellulose having 40% water detonates if confined and sufftcientiy activated. AH large-scale processes use nitric—sulfuric acid mixtures for nitration (127—132). 

Due to the strong ionic nature of lithium trifluoromethanesulfonate, it can increase the conductivity of coating formulations, and thereby enhance the dissipation of static electricity in nonconducting substrates (see Antistatic agents) (25). 

One of the benefits of an OMC is its immunity against static electricity and magnetic fields. Its capacity is 4.11 MByte in the version mentioned when used as a ROM, 2.6 MByte for the WORM version. 

Chemical treatments commonly appHed to cormgated paperboard packaging materials include additives that impart various degrees of water resistance, humidity resistance, oil and grease resistance, product abrasion resistance, product corrosion resistance, adhesion release properties, flame-retardant properties, nonskid properties, and static electricity control properties to the finished package (1,2). 

Liquid Fabric Softeners. The principal functions of fabric softeners are to minimize the problem of static electricity and to keep fabrics soft (see Antistatic agents). In these laundry additives, the fragrance must reinforce the sense of softness that is the desired result of their use. Most fabric softeners have a pH of about 3.5, which limits the materials that can be used in the fragrances. For example, acetals cannot be used because they break down and cause malodor problems in addition, there is the likelihood of discoloration from Schiff bases, oakmoss extracts, and some specialty chemicals. Testing of fragrance materials in product bases should take place under accelerated aging conditions (eg, 40°C in plastic bottles) to check for odor stabiUty and discoloration. 

Electrification is the process of producing an electric charge on an object. If the charge is confined to the object it is said to be electrostatic. The term static electricity refers to accumulated, immobile, electrical charges in contrast to charges in rapid flow, which is the subject of electrodynamics. 

Static electric discharge is a serious problem ia the electronics iadustry. Electronic devices are extremely seasitive to static electric discharges. Examples of the seasitivity to electrostatic discharge (ESD) are givea ia Table 2 (26). 

Electrostatic charges are also geaerated whea Hquids move ia coatact with other materials, Hquid or sofld, eg, duriag pumping of gasoliae. Serious iadustrial hazards caused by static ia chemical and related fields have been described (28), and a study of accidents ia the chemical iadustry revealed that 115 out of 1600 accideats, or 7%, were ascribed to static electricity (29) (see Plant safety). 

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