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Electrostatics

Viimati uuendatud: 11.10.2019


Electrostatics

Materials can either be conductive or insulating. Metallic worktops are conductive materials are, for instance, whereas worktops covered with plastic are insulators (non-conductors). Insulated worktops keep the electric charge and could increase it in time. Should this electric charge begin moving, electric current will generate and the case no longer involves static electricity. Static electric charge can also accumulate in ungrounded metallic worktops.

The working environment humidity and surface dirt of materials or tools can considerably influence the behaviour of charges. Thus, static electricity phenomenon is more common in dry weather than moist.

Contact with electrostatically charges surfaces can trigger an electric solution (“getting sparked”). Here, the electrical charge of the human body and the strength of the body’s connection with the ground surface are also relevant.

Regarding electrostatics, it is important to understand the natural principle that charged bodies (or surfaces) balance their loads when they come into contact – nature seeks balance. If the electric loads of two bodies are not considerably different, there will be no sparks.

Electric charge of surfaces grows as a result of industrial and other processes (e.g. rubbing the surfaces). If these surfaces are insulated from ground, the charge has nowhere to disperse and it builds up. When a sufficiently big charge has built up, people will “get sparked” if they touch the surface.

The following work processes are the typical creators of electrostatic fields:

  • pouring powders out of bags;
  • sifting / filtering;
  • transporting fluids, powders and other substances through pipes;
  • spraying fluids;
  • mixing fluids.

Fluids containing hydrocarbons (oil, kerosene, several solvents) possess a high electric resistance and could emit explosive/flammable fumes. These characteristics make the mentioned fluids especially vulnerable to hazards related to electrostatics. Great electrical resistance helps these substances to accumulate a large electrical charge. But flammable fumes could catch flames also from smaller electrostatic sparks.

The most frequent hazards are filters or splashes that occur during refuelling, or when foam or fumes occur during filling.

It must be noted that an electrostatic charge may accumulate both onto an insulator (e.g. plastic) or electric conductor (e.g. metal), if the latter is insulated from the ground.

Health Effects

Undesirable effects of the accumulated electrostatic charge are expressed in the lighter form as an unpleasant sense of “getting sparked” from a charged surface (e.g. when touching a door handle). More severe cases could result in death if the spark from the electrostatic solution should create an explosion or ignition in flammable or explosive gases or substances.

Physiological influences caused by the electrostatic charge vary from unpleasant stings to forceful reflexes. Stronger solutions can cause uncontrolled movements that can end with falling. The severity of physiologic influences depends on the amperage of the electric solution.

When the employee happens to hold a tool during such unwanted reflex, or if they are performing some responsible task, such uncontrolled movements may result in bodily harm to themselves or other people in the work zone.

As in the case of other electromagnetic fields, the strength of an electrostatic field is the greatest in the immediate vicinity (a few cm from the surface) and decreases exponentially when moving away from the object.

Prevention

The prevention of electrostatic fields concentrates on preventing the accumulation of static electricity on surfaces. Therefore, work surfaces are grounded; also employees and their clothes are grounded, if necessary. Accumulated charges are directed into the ground via the grounding wire, even before they can even begin to collect a charge. But not generating these fields at all would be the most effective way to eliminate the electrostatic fields.

The last resort are technical solutions for protecting sensitive devices against electrostatic solutions. But protecting devices does not exclude other hazards emanating from electrostatics: danger of ignition or explosion, and effect on people.

Work processes should be customized to minimize contact between such materials that generate static electricity when they come into contact with one another (e.g. glass and teflon; PVC and nylon).

Friction-generated electric charge can also be decreased by decreasing the speed of two materials that come into contact with one another. For example, the speed of the feed line transporting the cut material, or the flow of fluids in pipes is slowed down.

Grounding of Work Surfaces and Devices

The main solution of electrostatics’ prevention is to unify the difference of potentials between two objects (e.g. operator and device). This is mostly achieved via grounding.

Situations occur in which metallic work surfaces or devices insulated from the ground collect a charge via induction. In this way, a rather large charge can accumulate and acquire a great amount of energy.

Therefore, all metallic parts of devices that the employees have access to must be grounded. This principle can be extended to all metallic surfaces that the employee might come into contact with: door handles, frame-constructions, electronic components, containers (especially in the chemical industry), bodies of vehicles (that are used for hauling hydrocarbon-based materials).

If all electrically conductive parts and surfaces would be constantly grounded, their electrical potential would be the same, meaning that the hazards of the electric field and electric solution are minimized. However, achieving this situation is prevented by the fact that not all surfaces/materials are electric conductors neither can be turned into one. Also mobile devices (cars, wireless electronic tools) are impossible to ground.

Protection of Employees

If an employee does not wear footwear with special conductive soles or is not otherwise grounded, there is a good chance that an electrostatic charge will build up during the day on the body (and clothes). The charge might be grown by some synthetic materials (e.g. carpeting) or work processes.

To minimize the hazards emanating from an electrical solution, the following is possible:

  • decrease the unpleasant bodily effect by touching the grounded      surface previously with another metal object, like a key,
  • decrease the maximum current value by discharging the electrostatic      charge into a dispersive material (some special mat or discharging      bracelet, the exiting current of which is limited by a resistor).

Protection of Explosive Environments

The atmosphere of the working environment, containing some explosive gas or dust, can also be hazardous. Here, the following must be paid attention to:

  • improving air circulation; or
  • add combustion-decreasing gases into the internal atmosphere; or
  • decrease the oxygen level (which elimits the explosion hazard).

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