Electrostatic Charges

What are electrostatic charges?

Electrostatic charges are the excess or deficiency of electrons on the surface of a material, leading to an unbalanced electric charge. This phenomenon, commonly known as “static electricity,” can occur in both solids and liquids, including lubricants and fuels. Accumulation of electrostatic charges can lead to dangerous spark discharges, posing a risk of ignition of flammable vapors.

How do electrostatic charges form in lubricants?

Most lubricants, especially mineral oils and synthetic hydrocarbons, are dielectrics, meaning they are substances that poorly conduct electricity. Electrostatic charges can be generated and accumulated in them as a result of:

• Flow of liquid through pipelines, hoses, filters: Friction between the liquid and the walls of the conduits causes separation of charges.
• Pumping, mixing, spraying: Intense movement of the liquid promotes electrification.
• Filtering: Flow of oil through the filter material can generate significant charges.
• Contact and separation of different materials: E.g., liquid with machine components, tanks.

The degree of electrification depends on many factors, including the electrical conductivity of the liquid (the lower it is, the easier charges accumulate), flow speed, type of materials, and presence of contaminants (e.g., water).

Why can electrostatic charges be dangerous?

When a charged object (e.g., liquid in a container, device component) approaches another object with a different electric potential (e.g., grounded or oppositely charged), electrostatic discharge can occur in the form of a spark.

If such a discharge occurs in an atmosphere containing flammable vapor concentrations (e.g., gasoline, solvent, certain oils with low flash point) within their explosive limits, the spark can initiate an ignition or even explosion.

The risk is particularly high in cases of:

• Products with a low flash point.
• Operations conducted in confined or poorly ventilated spaces where vapors can accumulate.
• Use of non-conductive or improperly grounded installation elements (tanks, hoses, pumps).

Factors affecting charge accumulation

• Conductivity of the liquid: Liquids with low conductivity (e.g., < 50 pS/m) are more prone to charge accumulation.
• Flow speed: Higher speeds generate more charges.
• Installation material: Use of non-conductive plastics without proper grounding favors charge accumulation.
• Presence of dispersed phases: E.g., water droplets in oil, air bubbles.
• Temperature and ambient humidity.

Methods of prevention and hazard control

To minimize the risks associated with electrostatic charges, the following measures are applied:

1. Grounding and potential equalization: All metal parts of the installation (tanks, pipelines, pumps, dosing devices, packaging) and vehicles (e.g., tankers) must be effectively grounded. Before starting pumping, equalizing wires (called bonding) must be connected, e.g., to the delivering and receiving tank.
2. Use of appropriate materials: As much as possible, avoid using non-conducting plastics in parts in contact with flammable liquids or use antistatic materials.
3. Limit flow speed: Especially at the initial stage of filling tanks and with low conductivity liquids.
4. Antistatic additives: Special additives enhancing conductivity are added to some fuels and solvents to facilitate charge dissipation.
5. Atmosphere control: Provide good ventilation to avoid forming explosive vapor-air mixtures. In some cases, an inert atmosphere is used (e.g., tank nitrogen blanketing).
6. Appropriate work procedures and personnel training.

Products and operations particularly at risk

• Fuel handling (gasoline, diesel, aviation fuels).
• Using and transferring organic solvents.
• Working with some evaporative cutting oils.
• Cleaning and degreasing processes using flammable liquids.
• Operations in explosion hazard areas (ATEX).

Information regarding electrostatic hazards for a specific product can be found in its Safety Data Sheet (SDS). Always follow safety rules and local regulations concerning working with flammable substances.