By Frank Ross
Anyone who has ever slid across a car seat in wintertime and received a jolt of static electricity knows the importance of static grounding, even if they don’t practice it often. Workers whose jobs are performed in an environment where such a spark can create a deadly explosion do not have the luxury of ignoring this dangerous potential. Some high-risk operations are obvious, while others are not commonly considered volatile.
You may have noticed that when a gas tanker fills up an underground storage tank at your local convenience store, the driver always attaches a metal grounding cable before beginning his work. Although gasoline is an obvious liquid with significant risk of explosion, other more common items in our daily lives are equally dangerous under the right conditions. For example, given the right mixture of oxygen and air-borne particulates, even common flour can create a highly explosive atmosphere.
While flour explosions are a much larger risk in areas where large amounts of flour are handled such as mills or bakeries and large grain elevators where grain dust is common, it only takes a little flour to create an explosion. Once formed, a highly dispersed dust cloud of approximately two ounces of flour suspended in a cubic yard of air has tremendous explosive properties. If exposed to a spark or flame the flour dust particles will burn and if the dust cloud is large enough, a flash fire can create a serious explosion. In areas where dust clouds are common, static grounding is a mandatory safety precaution.
|Retract-A-Cable (RAC) is coiled corrosion-resistant orange vinyl-coated cable that makes it easy to ground everything from drums to vehicles using the REB2960 or another of the series of Static Grounding Clamps sold by Storm Copper.|
The data processing industry, as well as the facilities where semiconductors are manufactured is considered a hazardous location that requires a diligent static grounding system. Likewise, the information technology (IT) world has a primary concern in minimizing static electricity and circulating currents because of the need to protect sensitive electronic equipment from events that lead to equipment failure and data losses.
In hazardous locations such as chemical plants, grounding and bonding circuits are extremely important for safety of personnel as well as protecting the physical plant. When the potential for multiple sources of ignition are a primary concern in explosive atmospheres, a more enhanced protection system of handling static electricity is a common safety solution. Electrical engineering designs in these types of installations typically incorporate a system of static electricity protection.
All matter, whether liquid or solid, is made up of atoms. Atoms are either positively charged protons or neutrons with no charge. Together they form the nucleus or core of the atom while negatively charged electrons surround the nucleus. In their normal state, atoms are considered to be electrically neutral. Basically this means there are equal amounts of positive and negatively charge atoms present. Atoms can become “charged” when an excess, or a deficiency, of electrons is created relative to their naturally neutral state. Sparks from charged conductors that are ungrounded (including the human body) are responsible for most explosions and fires ignited by static electricity. Sparks are typically intense capacitive discharges that occur in the gap between two charged conducting bodies and the potential for an explosion or fire is directly related to the amount of energy contained in the discharge. A capacitor is basically two conductors separated by an insulating material. In the electrical phenomena known as a static discharge, the charge potential is generally separated by a resistive barrier such as an air gap or form of insulation between the conductors.
According to the National Fire Protection Association (NFPA), defines Static Electricity as an electric charge that is significant only for the effects of its electrical field component and that manifests no significant magnetic field component. And a Static Electric Discharge is the release of static electricity in the form of a spark, corona discharge, brush discharge, or propagating brush discharge that might be capable of causing ignition under appropriate circumstances. The NFPA notes the following conditions must be met to create the potential for an explosive static discharge.
1. An effective means of separating the charge must be present.
2. A means of accumulating the separated charges and maintaining a difference of electrical potential must be available.
3. A discharge of the static electricity of adequate energy must occur.
4. The discharge must occur in an ignitable mixture [NFPA 77 – 4.3.1].
The primary objective when addressing concerns and hazards of static electricity and stray voltages is to minimize, or hopefully eliminate, any differences of potential between electrically conductive objects and the ground. Grounding and bonding are two of the methods most often used to reduce the risk of static discharges.
The NFPA defines grounding as being connected to earth or to some conducting body that serves in place of the earth. By their definition, bonding is the permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed. The bonding process consists of connecting two or more conductive objects together by means of a conductor so they have the same electrical potential, but not necessarily at the same potential as the earth.
To eliminate confusion between these two terms, think of grounding as a connection or path to the earth to put electrically conductive materials at the same potential as the earth. Bonding is a physical connection of electrically conductive materials to eliminate differences in the potential between each individually, thereby forming one conductive mass.
Humidity is another factor in the equation that determines the potential for explosion from a static discharge. Generally speaking, when higher humidity is present the potential for an explosion is reduced. Other options for reducing ignition hazards from static electricity would include removing the ignitable mixture from the area where static electricity could cause a discharge capable of igniting the existing mixture. Another consideration would be reducing the generation or accumulation of a charge by means of process or product modifications. And the final option would be neutralizing the charges. To that end, grounding isolated conductors and ionizing the air are the two primary methods of neutralizing charges.
This information is not totally exhaustive about the causes or potential solutions for static discharges, but is intended to increase your awareness of the potential danger that exists. The analysis of risk and any potential solution for any situation should be evaluated by an engineering professional with expertise in this particular discipline. Once a solution has been determined, Stormgrounding.com has all the static grounding equipment necessary to keep your specific static electric hazards under control.
Shop online in our secure Web site, or for static-free service, give our friendly customer service staff a call on our toll-free line: 1-888-334-2177.