Electrostatic testing is a critical process in various industries, particularly those dealing with flammable materials, powders, gases, or sensitive electronic components. Its primary purpose is to assess materials, equipment, or working environments for their potential to generate, accumulate, or discharge static electricity, which can lead to significant risks such as ignition, explosions, fires, or electronic component damage.
Common tests include.
- Volume Resistivity
- Surface Resistivity
- Charge Decay (Relaxation) Time
- Breakdown Voltage
- Liquid Conductivity
- Flexible Intermediate Bulk Containers (FIBC)
- Electrostatic Chargeability Testing
and manage electrostatic hazards, ensuring safety, product integrity, and workplace standards are upheld. Top of Form
Prime Process Safety Center has the expertise in conducting electrostatic testing, utilizing highly experienced lab staff and state-of-the-art equipment ensuring compliance with regulatory bodies and offering complimentary recommendations for various applications.
Electrical volume resistivity is the electrical resistance measured across opposite faces of a cube of solid material with side length 1m. Â Volume resistivity is used to predict, indirectly, the low-frequency dielectric breakdown and dissipation factor properties of some materials. Volume resistivity determines how easily or difficultly electrical current passes through a material. Higher resistivity values indicate poor conductivity, while lower values signify better conductivity. Electrical volume resistivity is an intrinsic property of a substance, dependent on its composition, structure, and temperature. Insulators typically exhibit high volume resistivity, while conductors have low resistivity.
The volume resistivity test is conducted in accordance with the American Standard Testing Method (ASTM) D257. ‘Standard Test Methods for DC Resistance or Conductance of Insulating Materials’, BS 5958: Part 1: 1991 and BS 7506: Part 2: 1996, EN ISO/IEC 80079-20-2, and NFPA 77.
Volume Resistivity Test Cell
The volume resistivity (Ωm) of the material is classified as follows:
| <105 | Conductive / Low Resistivity |
| 105 to 109 | Static Dissipative / Medium Resistivity |
| >109 | Non-Conductive / High Resistivity |
By knowing the volume resistivity of your material, measures can be put in place to safely handle the material. This can be achieved by handling these materials in a well earthed environment (earthed conductive or static dissipative containers, silos, hoppers, and plant equipment). The build-up and retention of charge on a material or equipment possess the biggest threat if the charge is suddenly released in the form of a spark discharge, which can cause an ignition of a flammable atmosphere. Therefore, it is imperative to know and understand the electrostatic properties of your materials to ensure they are handled correctly to prevent discharges and potential ignition of flammable atmospheres.
Electrical surface resistivity is the electrical resistance of the surface of a material, in units of Ohms per Square (Ω/sq). The surface resistivity is independent of the material size or thickness. It is a calculated based on the surface resistance of the material and the known geometry of the electrodes. It signifies the material’s resistance to current flow when an electrical potential difference is applied to the surface. Surface resistivity differs from volume resistivity as it specifically addresses the electrical characteristics of a material’s surface layer, influencing its electrical behaviour in applications such as coatings, films, and insulating layers. Factors that could influence a material’s surface resistivity the material composition, surface treatments, moisture, temperature, contamination, and mechanical stress can impact surface resistivity. These factors alter the surface’s conductivity or insulation properties.
The surface resistivity test is conducted in accordance with the American Standard Testing Method (ASTM) D257. ‘Standard Test Methods for DC Resistance or Conductance of Insulating Materials’, BS 5958: Part 1: 1991 and BS 7506: Part 2: 1996, and NFPA 77.
Surface Resistivity Test Electrode
The surface resistivity of the material is classified as follows:
| <105 | Conductive / Low Resistivity |
| 105 to 109 | Static Dissipative / Medium Resistivity |
| >109 | Non-Conductive / High Resistivity |
By knowing the surface resistivity of your material, measures can be put in place to safely handle the material. This can be achieved by handling these materials in a well-earthed environment. The build-up and retention of charge on the surface of a material or equipment pose the biggest threat if the charge is suddenly released in the form of a spark discharge, which can cause an ignition of a flammable atmosphere. Therefore, it is imperative to know and understand the electrostatic properties of your materials to ensure they are handled correctly to prevent discharges and potential ignition of flammable atmospheres.
Charge Decay (Relaxation) Time
The charge decay time test is a method used to assess the ability of materials to dissipate or eliminate electric charges over time. This test measures the rate at which the charge dissipates from a material’s surface after it has been charged, often due to static electricity or electrostatic discharge (ESD). The rate of charge dissipation or relaxation is an essential characteristic for materials used in applications where the buildup and dissipation of static charges can impact performance, safety, or product quality. The charge relaxation time is performed in accordance MIL-STD-3010 , IEC-61340-4-4 and NFPA 77.
According to MIL-STD-3010, a material that relaxes its initial charge to 10% within 5 seconds is considered to be static dissipative material. By knowing the charge relaxation time of your material, measures can be put in place to safely handle the material. This can be achieved by providing proper earthing of equipment and personnel handling the material. Charge relaxation testing is crucial in industries involving electronics, manufacturing, packaging, and areas where static charges can impact product quality, safety, or functionality.
Electrostatic Charge Transfer Measurement
Electrostatic charge transfer refers to the movement or exchange of electric charge between materials or objects through contact or proximity, resulting in the redistribution of charges and potential differences between the surfaces involved. This phenomenon occurs due to the movement of electrons from one surface to another, leading to an imbalance of positive and negative charges. This test is designed to measure the charge transferred in electrostatic discharges from insulating surfaces. The test is best applied to brush discharges from material/ equipment surfaces and provides an alternative to determining discharge energy by ignition of local flammable gas mixtures. The charge transfer is performed according to IEC 60079-0 and IEC/TS 60079-32-1
Results is interpreted according the IEC 60079 standard table below providing classification of explosion groups of materials.
According to IEC 60079-0 and IEC/TS 60079-32-1, the maximum allowed surface area of insulating materials is limited in explosive atmospheres. However, there are many cases where a sufficient safety level is still achieved with insulating materials. These cases include surfaces with embedded corona tips, enclosures backed with printed boards as well as materials with an internal breakthrough voltage of only a few kilovolts. By knowing the maximum charge that can be transferred from an insulating material, the maximum allowed surface area can be determined to handle the material safely in an explosive atmosphere.
Breakdown voltage is the minimum voltage that causes a portion of an insulator to experience electrical breakdown and become electrically conductive. All dielectric materials have a maximum applied field at which they fail and begin to conduct charge, called the dielectric breakdown strength (or alternatively dielectric breakdown voltage). The breakdown occurs either by movement of charge carriers within the dielectric material, result of dielectric and/or Joule heating or compression by electrostatic forces. This breakdown is often accompanied by a sudden and substantial increase in conductivity, resulting in the formation of an electric arc or breakdown path through the insulator.
Breakdown voltage testing is performed in accordance with IEC 60243-1, ASTM D3755-20 and Section 9.2 of IEC 61340-4-4
In the presence of prolific charge generating mechanisms (e.g. pneumatic transfer of powders, charge spraying in the powder coating process) very high levels of surface charge can be generated on an insulating sheet or layer with earthed metal backing. If the breakdown strength of the layer is sufficient to withstand the large field strength in the layer, surface charge densities of the order of 300 μC/m2 enable the discharge to change from a brush discharge into a propagating brush discharge. A propagating brush discharge can release a lot of energy. It is, therefore, capable of igniting almost all flammable gases, vapors and powders and can cause severe electrostatic shocks. By knowing the breakdown voltage, appropriate measures can be put in place to avoid propagating brush discharges in an explosive atmosphere.
Sparks From Isolated Conductors and Insulators
The use of insulating materials can isolate metal plant components or other conductive objects from earth. By being close to charged material, such conductors can become charged by induction, charge sharing or by collecting sprayed charge or charged particles. These conductors can acquire a large amount of charge and energy and can store it for a long time. Most of that energy can eventually be released as an incentive spark to earth.
Igniting Power of Insulators
To determine the direct incendivity of discharges, the insulating material is charged under the worst-case conditions as highly as possible (at least to the maximum level that could occur in practice) to provoke discharges to an earthed sphere (ignition probe) approaching and to pass such provoked discharges through gas mixtures of the known MIE value. The test is conducted in accordance with IEC/TS 60079-32-1
Electrostatic Discharge (ESD) Testing
Isolated conductors and insulators can present hazardous conditions in a flammable atmosphere when they are electrostatically charged. This is primarily due to the retention of the charges within or on the surface of the materials. A series of electrostatic discharge testing such as charge transfer, igniting power, sparks from isolated conductors and insulators and charge transfer may be able to provide risk assessment for the use of such materials in a flammable atmosphere.
Electrostatic Chargeability Testing
Electrostatic chargeability refers to the property of materials that allows them to acquire an electric charge through friction, induction, or conduction without the flow of current. Objects become charged when electrons are transferred between them, leading to an excess or deficit of electrons, creating a net positive or negative charge.
This phenomenon arises from the behavior of charged particles, particularly electrons, within the atomic structure of materials. When two materials come into contact and then separate, electrons can be transferred, leaving one material positively charged (having lost electrons) and the other negatively charged (having gained electrons).
Electrostatic chargeability plays a crucial role in various fields, including industry, technology, and everyday life. It is the principle behind static electricity, which manifests in phenomena like lightning, the attraction of charged objects, and the function of devices such as photocopy machines and electrostatic precipitators.
Understanding electrostatic chargeability is fundamental in designing materials, developing technologies, and ensuring safety in environments where static electricity buildup can lead to hazards or disturbances in electronic equipment.
The test is conducted in accordance with ASTM D4470-97, ‘’Standard Test Method for Static Electrification’’.
For materials exhibiting high electrostatic chargeability, implementing safety measures is crucial to mitigate potential hazards associated with static electricity buildup. For example establishing a proper grounding system for the material and equipment to prevent the accumulation of excess charges. This involves connecting conductive materials to the ground to allow the dissipation of static charges. Bonding also ensures that different conductive materials are at the same electrical potential, minimizing potential differences that can lead to static discharge. Employing materials that are specifically designed to minimize static electricity buildup can also be implemented when material are determined to have high propensity to electrostatic charge. Anti-static materials have properties that allow charges to dissipate more readily, reducing the risk of accumulation. Higher humidity can help dissipate static charges more effectively, reducing the likelihood of electrostatic buildup on materials. Installing devices like ionizers or static eliminators in areas where materials with high chargeability are present based on test results can be very beneficial. These devices emit ions that neutralize static charges and prevent their accumulation on surfaces.
Liquid conductivity is the electrical resistance of uncharged fuel in the absence of ionic depletion or polarization. It is the electrical conductivity at the initial instant of current measurement after a DC voltage is impressed between electrodes. The test is designed to determine the rest electrical conductivity of liquids in the range 0.1 to 2,000 pico Siemens per meter (pS/m). The results find application in the assessment of electrostatic hazards since the generation and dissipation of electrostatic charge due to handling depends largely on the ionic species present which may be characterized by the rest (equilibrium) electrical conductivity.
The test is conducted in accordance with the principles of ASTM D4308: Standard Test Method for Electrical Conductivity of Liquid Hydrocarbons.
Materials are classified according to their conductivity as low, medium or high. Materials such as Toluene and Xylene have conductivities less than 100pS/m and are considered to be low while materials such as Hydrogen Sulfide have medium conductivities between 100 and 10,000pS/m. Materials such as Isopropyl Alcohol and Acetone have conductivities greater than 10, 000pS/m and considered to be high conductive liquids. A material with a low conductivity would be considered insulating and therefore prevent the dissipation of charge. With such materials, it is possible for accumulation of charges at hazardous levels to occur which may in turn lead ignition of locally flammable atmospheres. Liquids with medium and high conductivities may lead to conduction or dissipation of charges and therefore prevent accumulation at hazardous levels. Knowing the conductivity class of your process liquid would ensure proper handling practices such as earthing of conductive and static dissipative containers of such liquids.
Flexible Intermediate Bulk Containers (FIBC)
Flexible intermediate bulk containers (FIBC) are used in industry for storage and transport of powders and granules. They are commonly constructed from polypropylene fabric or similar strong and heavy-duty insulating materials. During the filling and emptying of the FIBC’s, electrostatic charges can be built up which accumulate on the product of the container. In the event of the release of the charge in the form of incendiary discharge, an ignition can occur in a flammable atmosphere.
FIBC testing is performed in accordance with IEC 60243-1, ASTM D3755-20 and IEC 61340-4-4
Type A FIBC are made from fabric or plastic sheet without any measures against the buildup of static electricity. These bags do not provide any protection against electrostatic discharges and are intended for use with non-flammable materials.
- Type B FIBC are made from fabric or plastic sheet designed to prevent the occurrence of sparks and propagating brush discharges. While they do not provide full protection against incendiary discharges, Type B bags reduce the risk of propagating incendiary discharges from the bag’s surface.
- Type C FIBC are made from conductive fabric or plastic sheet, or interwoven with conductive threads or filaments and designed to prevent the occurrence of incendiary sparks, brush discharges and propagating brush discharges. Type C FIBC are designed to be connected to earth during filling and emptying operations. These bags effectively dissipate electrostatic charges by facilitating grounding, preventing incendiary discharges and reducing the risk of ignition in the presence of flammable atmospheres.
- Type D FIBC are made from static protective fabric designed to prevent the occurrence of incendiary sparks, brush discharges and propagating brush discharges, without the need for a connection from the FIBC to earth. These bags prevent the accumulation of static charges on the bag’s surface and are suitable for handling materials that are at risk of ignition in flammable atmospheres.
What Services does Prime Process Safety Center offer
Prime Process Safety Center offers the following Reactive Chemical Consulting Services; Chemical Reaction Hazard Assessment, Calorimetric Studies, Chemical Compatibility Studies, Chemical Instability, Chemical Kinetics Evaluation, Process Dynamic Simulation, Self-Heating Evaluation and Analysis, Emergency Relief System Design, DIERS Technology for Two-Phase Relief System Design and Emergency Relief Effluent Handling System Design
Moreover, Prime Process Safety Center offers the following reactive chemical testing services Differential Scanning Calorimeter (Differential Scanning Calorimeter), Differential Thermal Analysis (Differential Thermal Analysis), Thermogravimetric Analysis (Thermogravimetric Analysis), Accelerating Rate Calorimeter (Accelerating Rate Calorimeter) and Vent Sizing Package (Vent Sizing Package)