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Understanding and Mitigating Static Electricity in Industrial Settings 

We have all experienced static electricity. It’s the invisible force that makes our hair stand on end or our clothes cling to us. While merely a nuisance in these instances, static electricity can also damage electronics and cause deadly explosions. This is especially true in industrial settings, where common industrial processes such as filling and mixing can create massive static charges and extremely hazardous conditions. To safeguard both persons and property, it is crucial to adhere to applicable safety standards and procedures. 

What is Static Electricity? 

Every object is made of atoms that are typically electrically neutral. They contain an equal number of protons (positive charge) within their nucleus and electrons (negative charge) surrounding the nucleus. Static electricity occurs when there is a separation of positive and negative charges within or on the surface of a material or between materials. Electrons may move from one object to another, leaving one object with a negative charge and the other with a positive. When the objects are separated they retain the charge imbalance.

Objects that have a positive or negative charge will attempt to become neutral again. The excess charge will flow to another object, known as an electrostatic discharge. The discharge, or spark, can be extremely dangerous when it occurs near explosive mixtures. This is especially true in industrial settings. 

 

Causes of Static Electricity in Industrial Settings 

Static electricity is a natural by-product of common industrial processes. In these settings, friction, contact and separation, and rapid heat changes can cause static buildup and discharge. Some common causes of static electricity in industrial settings include: 

  • Filling 
  • Spraying
  • Pouring
  • Mixing
  • Flowing 
  • Walking 

 

Filling

Static electricity is generated when a low conductivity liquid passes through a non-conductive pipe. Positive charges are carried away with the flowing liquid while negative charges can build on the pipe walls. Since the pipe is non-conductive, the static charge remains on the pipe walls. These conditions are dangerous for several reasons. First, near the end of fill pipes at the filling point, static discharge can cause flammable air to ignite. 

Second, the charges in the pipe can also create an electrostatic field. When this happens, objects with dangerous electrostatic potential that are outside of the pipe such as gaskets and clips can jump to any conductive object including people. Thus, proper grounding for static electricity for these potentially dangerous objects is crucial.

 

Spraying 

Electrostatic charges are often used when spraying surfaces with paint, powder coating, or clear coat. The spray gun essentially adds a charge to the substance as it leaves the gun. The surface that is being painted, such as metal or plastic, is grounded and attracts the charged particles from the gun. When the spray gun and/or surface are not properly grounded, the spray gun can ignite and cause the gun to shoot flames. 

 

Pouring and Mixing 

Both pouring and mixing can agitate liquids and add a charge to the substance or surrounding objects. The agitated substance can either emit static discharge or can ignite when it comes into contact with another charged object.

 

Flowing 

Friction is also caused by liquid or dry bulk flowing through a pipe, hose, or sprayer. This can create an electric charge that is subsequently discharged when it comes into contact with another object. This process is known as flow electrification. 

 

Walking

Workers generate friction by walking. For instance, their arms rub against them and their shoes interact with the floor. This friction can cause the human body to generate a stored electrical charge. When they move within proximity of another person, machine, or substance, the built-up charge is discharged. 

Static discharge from the human body is not insignificant. According to some experts, humans can release a charge of up to 50,000 volts that can create a spark with the energy of 500 millijoules (mJ). To put that in perspective, just 0.017 millijoules can ignite hydrogen, while 1-50 mJ can ignite fine flammable dust.

 

Ways to Control Static in Industrial Settings 

Given the prevalence and danger of static buildup in industrial environments, organizations must take adequate measures to safeguard persons and property. Several methods can be used to control static electricity. The two that are most commonly used are bonding and grounding.  

 

Bonding Static Electricity 

Bonding is a method that involves connecting two or more conductive materials with a conductor such as a wire. The conductor allows charges to flow freely between the objects to equalize the charge between the objects and reduce the likelihood of static discharge. 

 

Grounding Static Electricity 

Grounding static electricity involves connecting a conductive material directly to the earth using a conductor such as copper, steel, or a grounding rod. The conductor provides a path to the ground to drain static charge as it is produced. 

While grounding and bonding are similar methods for controlling static electricity, there are some important differences. First, bonding involves connecting two conductive materials to equalize their charges while grounding involves connecting one or more objects directly to the earth. Second, bonding does not eliminate static charge. Rather, it equalizes the charge which reduces the likelihood that a spark will occur. Proper grounding for static electricity, however, eliminates the charge. But note that bonding to a grounded object will eliminate static charge if the grounded object is also conductive or semi-conductive.

 

Other Methods for Controlling Static Electricity 

In addition to bonding and grounding, some additional methods can help control static electricity. 

 

Humidity 

The work environment itself also plays a critical role in the potential hazardousness of static discharge. Humid conditions help to remove discharge through moisture in the air while dryer conditions are more prone to static buildup. It is advisable to maintain a humidity level above 60% through the use of industrial humidifiers.  However, this is not always feasible. 


Additives 

Antistatic additives to certain types of liquids can help to increase conductivity and reduce electrostatic charge formation. 


Clothing and Materials 

Special clothing and materials such as flooring can help reduce static charges from accumulating when workers are moving. 


Controlled Filling

Reducing the speed of liquids reduces the generation of static charges. Depending on the type of liquid, a relaxation time of more than a minute can help static charges dissipate. 

 

Important Standards for Static Control in Flammable and Combustible Atmospheres 

 

NFPA 77: Recommended Practices on Static Electricity 

The National Fire Protection Association (NFPA) is a global nonprofit organization that delivers information and knowledge through more than 300 codes and standards. NFPA 77 provides guidance on “identifying, evaluating, and controlling static electric hazards for the purpose of preventing fires and explosions.”


American Petroleum Institute API RP 2003 

RP 2003 “presents the current state of knowledge and technology in the fields of static electricity, and stray currents applicable to the prevention of hydrocarbon ignition in the petroleum industry…”. 


CENELEC CLC/TR: 50404

The European Committee for Electrotechnical Standardization (CENELEC) together with ETSI forms the European systems for technical standardization. CLC/TR 50404 sets forth the code of practice for the avoidance of hazards due to static electricity. 

 


How to Ground Static in Trucks and Railcars 

When trucks and trains load and unload liquids and dry materials, friction can create static buildup. Tankers that are transporting propane, gas, or other flammable liquids can accumulate enough static electricity to emit 2,250 mJ. It only takes 24 mJ to ignite gasoline vapor and 26 to ignite propane.  


Tank and Trailer Grounding 

Both NFPA 77 and API RP 2003 provide standards for grounding tank trucks. Relevant requirements state that: 

  • All bonding and grounding should be in place before starting operations. 
  • Ground indicators, often interlocked with the filling system, are frequently used to ensure that bonding is in place. 
  • Where a bonding or grounding system is all metal, resistance in continuous paths should typically be less than 10 ohms. 

Using the right truck grounding system can help ensure that operators abide by applicable safety standards. The system should have circuits that prevent the transfer of fuel if a ground connection has not been made. A solution like Newson Gale’s Earth-Rite grounding system with Road Tanker Recognition (RTR) not only ensures a connection but also ensures that the resistance of the truck loading ramp structure to the ground is low enough to safely pass static charges off the tank truck to the earth. Moreover, the solution ensures that the resistance between the tank truck and the earth grounding point is 10 ohms or less.

 

Railcar Grounding 

Railcars differ from flatbed trailers and tankers since they feature their own grounding system. The railcar’s wheel assemblies have metal-to-metal contacts that are always grounded. Yet many railcars have wheel bearings that are not conductive, causing the rest of the carriage assembly to be electrically isolated. Moreover, the wear pads on the carriage cast also isolate the assembly from the tank and fitting. 

For this reason, the tank must be grounded to the loading and unloading ramps during transfers. A railcar grounding system allows operators to safely discharge static electricity. Ensure that you go with a system that shuts down transfers of fuel if the ground connection is lost to avoid a potentially fatal explosion. 

 

SafeRack’s Grounding, Overfill, and Monitoring Solutions 

Static electricity is a natural byproduct of many common industrial processes. Bonding and grounding static electricity are the most commonly used mitigation methods. The most advanced solutions such as SafeRack’s railcar and truck grounding systems offer additional safety features that ensure an adequate ground connection is maintained to boost safety and productivity. SafeRack’s dedicated team can also help you select and install the right equipment for your railcar and tank car operational needs.