Granulate electrostatic charging — electrostatics in plastics transloading

Granulate electrostatic charging: where the electrostatic charge comes from, the dangers in PE/PP transloading, how to limit it — earthing, type A/B/C/D big bags, reducing pneumatics. A practitioner's guide.

Autor: Aleksy Pasternak 25 March 2025 Aktualizacja: 4 April 2026 10 min czytania

Granulate transloading and electrostatics — SMIALA terminal in Chorula

Definition

Granulate electrostatic charging is the accumulation of electrostatic charge on the surface of plastic grains as a result of friction during transfer, transport and transloading — a phenomenon unavoidable with polymer granulates, which are very good insulators and do not drain off the charge spontaneously.

In terminal practice it is one of those problems that do not show up on an invoice yet can ruin an entire operation. Granulate that has become charged sticks to walls, dusts, cakes and causes trouble during filling and emptying. And in unfavourable conditions — with combustible dust or solvent vapours — it stops being a nuisance and becomes a real occupational safety risk. Over more than thirty years working with polyethylene and polypropylene I have learned to treat electrostatics not as a physical curiosity but as a process parameter that must be consciously controlled.

The mechanism — triboelectric charging

At the root of the phenomenon lies triboelectric charging, that is electrification by friction. When two surfaces come into contact and separate, a charge separation occurs at the boundary: one accumulates an excess of electrons and becomes negatively charged, the other positively. With granulate there are millions of these contacts per second. The grains rub against each other, against the walls of loading hoppers, against the big bag fabric, against the inner surfaces of pipes and ducts. Each such contact is a small charge separation.

The nature of the material itself is decisive. Polyolefins — PE and PP — are among the best insulators known to industry. The surface resistivity of untreated plastic can exceed 10^13 ohms, which means that once generated, the charge practically does not drain away. It accumulates and adds up until the potential on the grain surface or on the whole mass of material in the packaging reaches values measured in kilovolts. This is a fundamental difference from metals or conductive materials, where the charge immediately drains to earth.

Three factors amplify the phenomenon:

Intensity of movement. The faster and more violently a grain moves, the more contacts and the higher the charge. A calm, gravity chute charges the material less than driving it with an air stream.
Pneumatic transport under pressure. This is the most charging method of moving granulate. Compressed air accelerates the grains in the pipes to high speeds, multiplying friction against the walls — especially at the bends of the installation. That is why material coming out of a pneumatic line is sometimes charged to a very high potential.
A dry environment. Moisture forms a thin, conductive layer on the grain surface that facilitates charge drainage. In dry air — typical of the heating season — granulate charges far more strongly than at moderate humidity.

This is why the transloading method matters so much. The choice between pneumatics and gravity is not only a question of speed or angel hair — it is also a question of how strongly we charge the material before it reaches the recipient’s silo.

Consequences — from nuisance to hazard

Electrostatic charging has two faces. The first, everyday one, is the technological nuisances that lower quality and slow down work:

Grains sticking. Charged granulate clings to the walls of hoppers, pipes, the inside of the big bag and the silo tanker. Residue after emptying is greater, and at a material changeover the risk of mixing grades grows.
Caking and agglomeration. Electrostatically attracting grains form lumps that disturb the free flow of material and can clog hoppers or valves.
Dusting. Charged dust particles (fines) rise and settle on every surface instead of falling — worsening workstation cleanliness and occupational hygiene.
Difficult filling and emptying. Material that will not flow evenly lengthens the operation, forces packaging to be shaken and reduces process repeatability.

The second face is more serious. Accumulated charge seeks to discharge, and when the potential is high enough, an electrostatic discharge — a spark — occurs. In itself it may only be unpleasant (everyone knows the “zap” from a door handle), but in the presence of combustible dust or combustible solvent vapours the spark can become an ignition source. This is a real risk wherever the granulate contains a dust fraction capable of forming an explosive dust-air atmosphere, or where vapours of volatile substances are present nearby. At a transloading terminal, where large masses of material are handled and dust is generated, this hazard must not be underestimated.

It is worth adding that brush and cone discharges are particularly dangerous. The latter appear above a cone of heaped bulk material in a large container — for example in a big bag or silo during filling — and can release energy sufficient to ignite sensitive dusts. This is one of the reasons why the electrostatic classification of packaging is so important.

Ex zones and big bag types A/B/C/D

Wherever there is a risk of forming an explosive atmosphere, the rules of working in explosion-hazard zones (Ex) apply, regulated by the ATEX directive. In such conditions, the choice of packaging ceases to be a matter of price and becomes a safety decision. The classification of big bags (FIBC) in terms of electrostatics divides them into four types:

Type	Properties	Earthing	Application
A	ordinary PP fabric, no antistatic protection	not applicable	non-combustible materials, environment free of combustible dusts and vapours
B	reduced breakdown voltage, limits the energy of spark discharges; does not drain off the charge	no	when no combustible vapours are present and the dust has a low ignition energy
C	conductive fabric with a grid of threads, requires connection to earth	yes, mandatory	combustible materials, Ex zones — provided correct earthing
D	dissipative fabric, disperses the charge without earthing	no	Ex zones without the possibility of reliable earthing; sensitive to soiling

A key pitfall concerns type C: a conductive big bag with an unconnected earth is more dangerous than an ordinary type A, because it behaves like an isolated conductor, accumulating charge over its entire surface and capable of releasing it in a single, strong discharge. That is why the discipline of connecting the earth at every filling and emptying of type C is absolute. Type D is more convenient in this respect, because it does not require a connection, but it loses its properties when its surface is covered with an insulating layer of dirt.

How to limit electrostatic charging

In terminal practice there is no single miracle remedy — there is a set of measures applied together, chosen to suit the material and the environment. Here are those that really work:

Limiting pneumatics, that is gravity. This is a measure at the source. Since pneumatics under pressure charges material most strongly, the most effective way to limit the charge is to give it up wherever possible. Our transloading without pneumatic conveying is based on a gravity chute through a sieve — the grain falls under its own weight, is not accelerated in pipes, and therefore charges incomparably less. This is an example of a situation in which the method protecting against angel hair and contamination simultaneously protects against excessive charge.
Earthing. Everything conductive — hoppers, pipes, frames, type C big bags — must have a reliable path for charge to drain to earth. Sound, controlled earthing is the foundation of safety in Ex zones and the first thing checked before starting an operation.
Ionisation. Air ionisers generate ions of both signs that neutralise the charge accumulated on the surface of the material and the packaging. They are used locally, in the loading zone, where the charge is highest.
Humidity control. Maintaining moderate air humidity in the hall facilitates the natural drainage of the charge. It is a simple, cheap and often underrated measure — especially valuable in the dry heating season.
Choice of antistatic packaging. A conscious choice of type C or D instead of type A wherever the material is combustible or the environment requires it. The choice of packaging is part of operation planning, not chance.

In daily work we most often combine these measures: the gravity chute limits charge generation, earthing and the right big bag type drain off what arises anyway, and humidity control and ionisation complete the picture. This is a layered approach — no single measure is a hundred percent, but their combination brings the risk down to an acceptable level.

The discipline of personnel also matters. Operators working with materials in Ex zones must wear antistatic footwear and clothing, and keep the workstation clean, because a layer of dust can worsen the properties even of a well-chosen package. Electrostatic safety is as much a matter of equipment as of habit.

Standards and classification

Electrostatics in the bulk materials trade is not left to intuition — it is regulated by standards. The most important is the IEC 61340 set, devoted to static electricity:

IEC 61340-4-4 defines the classification of big bags (FIBC) in terms of electrostatic properties — it is here that types A, B, C and D and their test methods are formally described.
IEC 61340-4-9 concerns flexible intermediate packaging and related products.
IEC 61340-5-1 describes the general requirements for protecting devices against electrostatic discharges and is sometimes a reference point for general rules.

They are complemented by the ATEX directive together with standards for selecting equipment and protecting against explosion in dust and gas atmospheres. In practice this means that for a given material and a given zone, the permissible packaging types, earthing requirements and rules for organising work are determined. A serious operator does not improvise — they work according to classified zones and a documented risk assessment. For a recipient auditing a supplier, compliance with these standards is one of the elements of assessing the reliability of a logistics partner.

Electrostatics in practice at the Chorula terminal

At our terminal in Chorula — by the A4 motorway, with a buffer warehouse for 2000 big bags and a throughput of up to 200 tonnes per day — electrostatics control is built into the very method of work. The cornerstone is gravity transloading without pneumatic conveying: by giving up accelerating the grains with compressed air, we limit charging at the source and at the same time protect the granulate from angel hair and contamination. The same solution serves three goals at once — and that is precisely why it makes sense.

Most of the granulates we handle — the polyolefins PE and PP — are strongly insulating materials, so we approach electrostatics cautiously by default. The terminal profile covers free-flowing materials, non-ADR, but every material with a dust fraction or elevated flammability we treat separately: with the right big bag type, verified earthing and — when needed — additional measures. Recipients from the plastics industry expect material that is not only clean but also safely transloaded, and electrostatics control is part of that promise.

You will find the full transloading offer, with quality and safety control maintained, on the page about transloading big bags to a silo tanker, and the broader context of bulk material transport in the PHS Magnum portal.

Sources

The IEC 61340 series of standards on static electricity, including IEC 61340-4-4 (FIBC classification) and IEC 61340-4-9 (flexible packaging).
The ATEX directive and guidelines for explosion protection in dust and gas atmospheres.
Industry materials on electrostatics in the transport and transloading of plastics.
Observations from working with polyolefins at the terminal in Chorula — Aleksy Pasternak.

Najczęstsze pytania (FAQ)

What is granulate electrostatic charging?

It is the accumulation of electrostatic charge on the surface of plastic grains during friction — during transfer, transport and transloading. Polyolefin granulates such as PE and PP are very good insulators, so the charge does not drain away freely and can build up to a high potential. The result is grains sticking together, dusting and, in extreme conditions, the risk of a discharge.

Where does the charge on granulate come from?

From triboelectric charging, that is electrification by friction. When grains rub against each other and against the walls of pipes, hoppers or the big bag, a separation of charges occurs at the interface of two materials. The more intense the movement and the more insulating the plastic, the higher the potential. Pneumatic transport under pressure amplifies the phenomenon, because it accelerates the grains and multiplies the number of contacts.

What are the dangers of granulate electrostatic charging?

On a daily basis it is grains sticking to walls, caking, dusting and difficulty in filling and emptying packaging. The more serious problem is the risk of an electrostatic discharge, which in the presence of combustible dust or combustible solvent vapours can become an ignition source. That is why, in explosion-hazard zones, electrostatics is treated as a real occupational safety risk.

Which type of big bag is antistatic?

Type A has no antistatic protection. Type B limits the energy of spark discharges but does not drain off the charge. Type C is conductive and requires earthing during filling and emptying. Type D is dissipative and disperses the charge without earthing. The choice of type depends on the flammability of the material and the working environment.

How can electrostatic charging be limited during transloading?

Most effectively by limiting pneumatics and using a gravity chute that does not accelerate the grains. In addition: earthing of the installation and conductive packaging, air ionisation in the loading zone, humidity control (a dry environment favours charging) and the choice of antistatic packaging of type C or D. In Ex zones all these measures are applied together.

Does humidity affect granulate electrostatics?

Yes, strongly. Moisture forms a thin, conductive layer on the grain surface that facilitates charge drainage. In dry air, typical of the heating season, granulate charges noticeably more strongly. That is why maintaining moderate humidity in the transloading hall is sometimes a simple and effective way to limit the problem.

Which standard regulates electrostatics in transloading?

The basic set of standards is the IEC 61340 series, including IEC 61340-4-4 on the classification of big bags (FIBC) in terms of electrostatic properties and IEC 61340-4-9 for flexible packaging. They are complemented by the ATEX directive and standards for selecting equipment for explosion-hazard zones. It is in them that types A, B, C, D and the requirements for their use are defined.