What is electrostatic testing?
Electrostatic testing is a critical process across many industries—especially those involving flammable materials, powders, gases, or sensitive electronic components. Its primary purpose is to evaluate materials, equipment, or work environments for their ability to generate, accumulate, or discharge static electricity. Left unmanaged, static electricity can pose serious risks such as ignition, explosions, fires, or damage to electronics.
Common electrostatic tests include surface resistivity, volume resistivity, charge relaxation, breakdown voltage, and so on. In this article, we provide a general guide to electrostatic testing, explaining how each test helps identify and mitigate hazards to ensure safety, product integrity, and compliance with workplace standards.
Volume Resistivity
Electrical volume resistivity measures a material’s resistance to electrical current flowing through its volume. It’s typically measured across opposite faces of a cubic sample and indicates how easily current moves within the material. This property depends on the material’s composition, structure, and temperature. Insulators have high volume resistivity, while conductors show low values. The test applies direct current voltage across a sample using electrodes and measures the resulting resistance to calculate resistivity.
Understanding volume resistivity is important for safely handling powders or solids that may hold static charge. Materials with high resistivity often retain charge, increasing the risk of electrostatic discharges that could ignite flammable atmospheres. Knowing a material’s resistivity helps organizations apply proper grounding or use conductive equipment to prevent sparks. Accurate data also supports compliance with safety standards and improves risk management in industrial settings.
Volume resistivity testing is performed according to recognized standards such as ASTM D257, which covers DC resistance or conductance of insulating materials. Additional standards include BS 5958: Part 1: 1991, BS 7506: Part 2: 1996, EN ISO/IEC 80079-20-2, and NFPA 77.
Surface Resistivity
Electrical surface resistivity measures how much a material resists electrical current across its surface, expressed in ohms per square (Ω/sq). Unlike volume resistivity, it specifically focuses on the surface layer—an important factor for coatings, films, and insulating layers. This property depends on several factors, including material composition, surface treatments, moisture, temperature, contamination, and mechanical stress. To test it, technicians apply direct current voltage across two electrodes placed on the material’s surface, often under different humidity levels to simulate real-world conditions.
Understanding a material’s surface resistivity is key to managing electrostatic hazards. In particular, it’s critical in applications where static charge buildup must be controlled, such as protective clothing liners or laminate sheets. Materials with high surface resistivity can retain charge longer, which increases the risk of discharge sparks in flammable environments. Therefore, knowing this property helps organizations implement proper grounding and use static-dissipative tools. As a result, they can reduce risk, enhance safety, and meet relevant industry standards.
Surface resistivity testing follows established standards like ASTM D257, BS 5958: Part 1: 1991, BS 7506: Part 2: 1996, and NFPA 77.
Charge Decay (Relaxation) Time
Charge decay time shows how quickly a material releases electric charge from its surface after being charged—an essential factor in controlling static electricity and preventing electrostatic discharge (ESD). Technicians start by conditioning the material at 50% relative humidity. They then charge the surface to about 5000 volts using corona discharge or triboelectrification and apply a grounding cable to initiate discharge. A static monitor measures how fast the charge dissipates and records the time it takes to drop to 50%, 10%, and 1% of the initial charge. This method works for both solid and powder materials and helps evaluate how well a material controls static buildup over time.
Understanding the charge relaxation properties of materials is vital in industries where static charge accumulation can affect safety, product quality, or operational performance, such as electronics, manufacturing, and packaging. Materials classified as static dissipative are those that reduce their surface charge to 10% within 5 seconds, according to MIL-STD-3010. Knowing this behavior allows for the implementation of proper grounding measures and handling procedures to mitigate the risk of static discharge, which can damage sensitive components or ignite flammable environments. Charge decay testing helps in selecting materials that balance conductivity and insulation for effective static control.
Charge decay testing follows established standards including MIL-STD-3010, IEC-61340-4-4, and NFPA 77.
Electrostatic Discharge (ESD) Testing
Electrostatic charge transfer refers to the movement or redistribution of electric charges between objects or surfaces through contact or proximity. This typically occurs when insulating materials or isolated conductors become electrostatically charged, often through friction or exposure to a charged environment. When these materials come into contact with or near a grounded object, a discharge may occur. This phenomenon is central to understanding how static electricity can accumulate and eventually be released in the form of sparks, even in the absence of a continuous conductive path.
Understanding and measuring electrostatic charge transfer is crucial in environments where static discharges can present serious hazards. In industries handling flammable gases, vapors, powders, or dust, unintentional discharges can ignite explosive atmospheres, leading to fires or catastrophic incidents. Charge transfer testing helps assess the ignition risk posed by insulating materials and isolated conductors by measuring the potential energy released in a discharge. This allows engineers and safety professionals to design systems that minimize static-related hazards, whether through grounding, material substitution, or implementing protective equipment like static eliminators.
Testing for electrostatic charge transfer is conducted in accordance with IEC 60079-0 and IEC/TS 60079-32-1.
Breakdown Voltage
Breakdown voltage is the minimum voltage at which an insulating material fails to resist electrical current, causing electrical breakdown and sudden conductivity. This occurs when the electric field exceeds the material’s dielectric strength, allowing charge carriers to pass through. Dielectric heating, Joule heating, or electrostatic compression often trigger the breakdown, leading to arcing or forming a conductive path. To test this, technicians condition solid insulating materials at 25% and 60% relative humidity and 23°C for at least 12 hours. They place the sample on a grounded plate, apply a cylindrical electrode, and gradually increase the voltage until a sudden current surge signals breakdown. Multiple tests on different surface areas and sides help ensure consistent results.
Measuring breakdown voltage is essential for safely using insulating materials like sheets, films, fabrics, foils, coatings, and Flexible Intermediate Bulk Containers (FIBCs). High surface charge densities from processes like pneumatic powder transfer or powder coating can generate strong electric fields. These may trigger brush or propagating brush discharges, which release energy and can ignite flammable atmospheres. Knowing breakdown voltage helps prevent such hazards by guiding material selection and safety measures. It also plays a key role in designing insulation systems and preventing failures under high voltage stress.
Breakdown voltage testing adheres to international standards such as IEC 60243-1, ASTM D3755-20, and IEC 61340-4-4.
Liquid Conductivity Testing
Liquid conductivity measures how well an uncharged liquid conducts electricity when a direct current (DC) voltage is first applied—before ionic depletion or polarization can occur. This test captures the liquid’s rest or equilibrium conductivity, usually ranging from 0.1 to 2,000 pico Siemens per meter (pS/m). The ionic species in the liquid play a key role in how electrostatic charge builds up or dissipates during handling. This test is especially important for fuel liquids. Before testing, technicians measure the liquid’s temperature, since it directly affects conductivity. They then apply a DC voltage between an outer cylindrical electrode and an inner electrode immersed in the sample, and use a pico-ammeter to record the current exactly three seconds later. To maintain accuracy, they thoroughly clean and flush the test cell with the liquid before taking measurements.
Understanding liquid conductivity is key to managing electrostatic hazards, especially when working with fuels and industrial liquids. Low-conductivity liquids like toluene and xylene act as insulators, allowing static charge to build up and potentially ignite flammable atmospheres. In contrast, conductive liquids like hydrogen sulfide or isopropyl alcohol help dissipate charges and reduce static risk. Conductivity testing guides safe handling practices, such as grounding containers and equipment to prevent ignition. It also helps assess liquid quality, purity, and suitability for specific industrial uses, making it valuable across many sectors.
Liquid conductivity testing is conducted according to ASTM D4308.
Flexible Intermediate Bulk Containers (FIBC)
Flexible Intermediate Bulk Containers (FIBCs), or bulk bags, are widely used to store and transport powders, granules, and other bulk materials. Made from strong polypropylene or similar insulating fabrics, these containers can accumulate static charge during filling and emptying. This buildup can trigger incendiary discharges, which may ignite flammable atmospheres if unmanaged. To evaluate and classify FIBCs, tests measure breakdown voltage, surface resistivity, conductivity, and discharge behavior under controlled temperature and humidity. These results help determine the container’s electrostatic safety performance.
Electrostatic testing of FIBCs is critical for ensuring safe handling of potentially flammable materials. Depending on their electrostatic properties, FIBCs are classified into types A, B, C, and D, each with distinct safety features to prevent ignition hazards. Type A bags provide no protection against static buildup, making them suitable only for non-flammable materials. Type B and C bags incorporate measures to reduce or dissipate charges, with Type C requiring grounding to prevent sparks. Type D bags offer static protection without the need for grounding by preventing charge accumulation altogether. Understanding these classifications and their implications allows manufacturers and users to select the correct FIBC type, minimizing the risk of fire or explosion in hazardous environments. Regular testing throughout product development, manufacturing, and periodic inspections ensures continued compliance and safety.
FIBC electrostatic testing is performed in accordance with internationally recognized standards including IEC 61340-4-4, IEC 60243-1, and ASTM D3755-20.
Electrostatic Chargeability Testing
Electrostatic chargeability is a material’s ability to acquire an electric charge through friction, induction, or conduction—without current flow. This happens when electrons transfer between objects during contact and separation. One material gains electrons (negative charge), and the other loses them (positive charge). This electron behavior is central to static electricity and affects many natural and industrial processes. To test chargeability, technicians subject solids or powders to controlled rubbing or flow and measure the charge using static field meters or Faraday cups with electrometers.
Understanding chargeability is essential in industries where static buildup can cause safety hazards, equipment failure, or process issues. Materials with high chargeability can ignite flammable environments or damage electronics. Measuring this property helps identify materials that need grounding, bonding, or anti-static treatments. Managing humidity and using static eliminators also help reduce risks. Regular chargeability testing supports material development, quality control, and safe handling in industrial operations.
Electrostatic chargeability testing is conducted according to established protocols such as ASTM D4470-97, “Standard Test Method for Static Electrification.”
Conclusion
Managing electrostatic risks is crucial for safety and reliability in industries handling powders, granules, and bulk materials. Static charge buildup can cause serious operational and safety issues. This guide to electrostatic testing explains how understanding material behavior helps reduce these risks. Electrostatic testing—for solids, powders, or packaging—provides key data for material selection, equipment design, and environmental controls. By assessing how materials respond to contact, friction, or flow, organizations can prevent static-related incidents and improve process safety.
At Prime Process Safety Center, we bring deep industry knowledge and advanced lab capabilities to every project. We deliver accurate, reliable data that meets tough industry and regulatory standards. Whether you’re developing new products or validating existing ones, our team works closely with you to provide practical insights and custom recommendations.
Partner with us for trusted process safety testing. With modern equipment, strict quality controls, and a strong commitment to safety, we help you reduce static hazards and improve material handling. Our goal is to help you operate safely and confidently in high-risk industrial environments.
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