FIBC Types A, B, C and D Explained
“Static electricity is the one FIBC risk that is invisible until it is not.”
Executive Summary
Filling and emptying bulk bags moves metric tons of dry material rapidly against polymeric fabric, inducing significant triboelectric static charges. In the presence of combustible dusts or flammable solvents, this static charge can trigger devastating flash fires. International standard IEC 61340-4-4 classifies FIBCs into four distinct types.
Understanding Triboelectric Hazards
When powder flows through an FIBC at high velocity, electrons transfer across the contact surfaces. The resulting static voltage can easily exceed 20,000 volts.
If the discharge energy exceeds the Minimum Ignition Energy (MIE) of the surrounding dust cloud or solvent atmosphere, an explosive spark occurs. Selecting the right FIBC type is a non-negotiable process safety mandate.
Type A — Standard Plain Woven Polypropylene
Type A bags are fabricated from plain polypropylene fabric without any antistatic treatments. Surface charges build up without mitigation.
• Safe for: Non-flammable dry materials (sand, gravel, agricultural grains, fertilizer).
• Prohibited for: Combustible dusts (MIE < 1000 mJ) or any area containing flammable solvent vapours.
Type B — Low Breakdown Voltage Fabric
Type B fabric does not dissipate static charges, but it is manufactured with a breakdown voltage strictly below 6 kV across the fabric wall.
This critical breakdown limit prevents propagating brush discharges — high-energy sparks capable of igniting dust clouds.
• Safe for: Dry combustible powders where minimum ignition energy is above 3 mJ, provided no flammable gases or vapours are present.
• Prohibited for: Any atmosphere containing flammable gases, solvent mists, or hybrid atmospheres.
Type C — Conductive & Groundable
Type C bags incorporate interwoven conductive grid threads spaced across the entire fabric, interconnected to dedicated grounding tabs.
During filling and discharge operations, the grounding tab must be physically clamped to an approved plant earth. All electrostatic charges drain safely into ground before voltage can accumulate.
• Crucial requirement: Must be grounded during every cycle. An ungrounded Type C bag is more dangerous than Type A, as isolated conductive threads create high-energy capacitance.
Type D — Antistatic / Static Dissipative (No Grounding Required)
Type D bags use patented dissipative yarn technologies that safely discharge static energy directly into ambient air via low-energy corona discharge.
They do not require grounding wires, making them ideal for facilities where human grounding discipline cannot be 100% guaranteed.
• Caution: Bag fabric must not be painted, oily, or contaminated with conductive grease, which could ground the corona filaments.
Classification Decision Matrix
Always base your FIBC type selection on a documented DSEAR/ATEX hazardous area classification and laboratory powder MIE test data.
| Material Environment | Dust Cloud MIE | Vapour Atmosphere Present? | Required FIBC Type |
|---|---|---|---|
| Non-flammable inert solids | N/A | No | Type A |
| Combustible dusts | > 3 mJ | No | Type B |
| Combustible dusts | Any MIE | Yes (Solvents/Vapours) | Type C (Grounded) or Type D |
| Flammable atmospheres with risk of ungrounded human error | Any MIE | Yes | Type D |
Coastal FIBC Technical Engineering Desk · Rajkot, India
Have specific material or electrostatic calculations? Send your inquiry to our engineering team.