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Recognizing and Mitigating Static Electricity Hazards
Ancient Greeks discovered that when animal fur and amber were rubbed together, the fur could be used to attract feathers, glass dust and other lightweight objects. It wasn’t until 1600 AD, however, that William Gilbert, an English scientist, documented and associated this property with electricity.
Static electricity is sometimes little more than a nuisance that causes clothing to unattractively cling in all the wrong places. But it can be much more detrimental. In fact, fire departments respond to nearly 280 industrial incidents involving static electricity each year, according to the National Fire Prevention Association (NFPA).
Imbalance of Energy
Objects are made of atoms containing protons, electrons and neutrons. Most of the time, the protons and electrons balance each other in an object, making it electrically neutral. But when different objects rub together, that friction can cause the number of protons or electrons on the surface can become imbalanced, creating static electricity.
Static electricity remains on a surface until it is either safely discharged or until it can jump to another object. When it finds a path to jump to another surface, it does so as a spark.
Although it is most often associated with a person walking across a surface and touching another person or a metal object, static electricity can also be generated by materials in motion, such as the movement of fluids. When liquids move through pipelines or hoses, the friction creates static electricity.
Filtering, stirring, pouring and pumping liquids creates static electricity. Like static cling in clothing, this is sometimes little more than a nuisance, but when flammable liquids are being moved, static electricity can cause fires and explosions if sufficient concentrations of flammable vapors are present.
Like friction, humidity plays a role in static electricity hazards. According to the National Oceanic and Atmospheric Administration (NOAA) data, 89 percent of the US experiences at least seasonal conditions where the relative humidity is 60 percent or less. The lower the humidity, the higher the potential for harmful levels of static electricity to build up on surfaces.
The fluctuation between seasons, or between humid and arid conditions, can lure some facilities into a false sense of security—especially if static electricity is not a hazard for long spans of time. That’s why it is important to recognize potential sources of static electricity and guard against them all the time, not just when the humidity drops.
Sometimes, safety hazards are easy to spot because they can be seen. Because static electricity cannot be seen, sources may initially be harder to identify.
Reviewing chemical inventories is one place to start. Look for all liquids that are flammable, such as petroleum-based solvents and fuels. When these fluids are in motion, their hazard potential increases more than when they are in undisturbed, closed containers. Identify areas where each flammable liquid is pumped, mixed, filtered, sprayed, poured or transferred as well as areas where flammable vapors may be released from a process.
Combustible dusts are another hazard to consider. More than 100 industrial combustible dust incidents were confirmed by the Chemical Safety Board from 2006 to 2017, and they weren’t only happening at grain handling facilities. Like flammable vapors, static electricity can produce a spark with enough energy to ignite combustible dusts in the air or on surfaces.
After considering liquids and dusts, note each static-generating activity and process. Conveyor belts, fan blades, pulleys, sanding and grinding operations, receiving and assembly activities are all common examples. People, machinery and motorized vehicles are additional sources.
Next, decide where the combination of a liquid, gas or dust and an activity or process can create the potential for static electricity to unsafely discharge. In addition to manufacturing, assembly and distribution areas, do not overlook outdoor bulk chemical and waste storage areas.
Bonding and Grounding
Think back to middle school science class when the teacher discussed electricity. When it comes to the flow of electricity, materials are either conductors or insulators. Conductors allow electricity to flow freely. Insulators interrupt the flow of electricity.
Materials made of metal are generally good conductors. These materials can be bonded and grounded to increase safety and decrease the risk of static electricity discharging. Materials made of plastics or elastomers are typically insulators. These materials cannot be effectively bonded our grounded.
Static electricity can build to unsafe levels on both conductors and insulators. Grounding items that are conductors, such as drums, totes, metal cabinets and metal machinery, creates a path for static electricity to be safely dissipated to the earth. This is usually accomplished by using a grounding cable to connect the metal item to a grounding assembly or to an unpainted water pipe.
In some instances, even people need to be grounded. This is accomplished though specialized flooring and grounding assemblies worn over the shoes or on the wrists.
Bonding prevents the spark from built up static electricity from jumping between two objects by connecting them to equalize their potential energy. A good example of this is bonding a pump to a drum containing a flammable liquid, then bonding a smaller container to the pump before pumping the flammable liquid into it. When the drum is properly grounded, the bonding assemblies provide a path from the receiving container through the bonding assemblies so that any built up static electricity on a person or any of the bonded surfaces can be safely channeled to the earth.
Non-conductive materials, like plastics and polymers, cannot be effectively bonded and grounded. These materials also tend to have an inherent static charge. Increasing humidity in areas where non-conductive materials are used or stored can help to reduce static hazards.
Storing Flammable Liquids
Because static electricity can build up on any surface, flammable liquid storage areas cannot be ignored. Drums and smaller containers should be kept in designated areas and grounded. In many cases, smaller amounts of flammable liquids may be kept in flammable storage cabinets.
Metal flammable storage cabinets have a brass screw, typically on one side of the cabinet near the bottom, to facilitate grounding. When metal containers are placed in the cabinet, the grounding assembly will channel static electricity to the earth.
When drums and other containers are not in use, keeping them closed will help to prevent flammable vapors from being released. Minimizing these vapors can help to prevent unsafe levels from forming in the air and can prevent an explosion if a stray spark of static electricity is left unchecked.
Like gravity, static electricity is an unavoidable property that cannot be overlooked or disregarded. Recognizing it as a hazard and proactively mitigating it when working with flammable liquids and combustible dusts will help to prevent dangerous fires and explosions.
This article originally appeared in the June 2020 issue of Occupational Health & Safety.