FIBC Type C vs Type D: Choosing an Antistatic Bulk Bag

Dry powders charge up whenever they move — pneumatic filling, discharge through a spout, even pulling out a liner. In a dust cloud, one spark is enough. The energy needed to ignite that cloud is its minimum ignition energy (MIE): fine carbon black and organic pigments can sit below 10 mJ, while coarse cement dust needs far more. That number, not the product name, decides which bag class is safe.

The four classes at a glance

• Type A — plain woven PP, no static protection. Non-hazardous areas only.
• Type B — same fabric, breakdown voltage at or below 4 kV, which stops propagating brush discharges. Still no earth connection.
• Type C — conductive threads or filaments interwoven, plus a grounding tab. Must be earthed during filling and emptying. IEC 61340-4-4:2018 caps resistance to the designated earth point at 100 MΩ, raised from 10 MΩ in earlier editions.
• Type D — dissipative coating or fibre, no earthing required; charge is bled off by corona discharge.

Type C: safest, if it is actually grounded

Type C physically drains charge to earth, which makes it the default for low-MIE powders, solvent-borne products and areas where gas may be present. The catch is operational: an ungrounded Type C bag behaves like a Type A bag. Most field failures trace back to a missing clamp, a painted or rusty filling frame, or a clamp hooked on after filling has already begun. Three controls close that gap — a dedicated earth stud on the filling head, an interlock that blocks filling until the resistance check passes, and a clamp inspection every shift.

Type D: no grounding, but a hard limit

Type D is the practical answer where a reliable earth cannot be guaranteed: mobile filling stations, temporary discharge pits, third-party warehouses. NFPA 652 permits Type D for combustible particulate solids and for flammable vapour atmospheres with an MIE above 0.14 mJ. Below that threshold — hydrogen, carbon disulfide, some solvent vapours — Type D is not acceptable and grounded Type C is required. People and conductive equipment around a Type D bag should still be earthed.

Decision checklist

• Low-MIE powder (carbon black, organic pigment, fine chemical) on a fixed, grounded filling line → Type C with a grounding interlock.
• Same powder, but loading points move or earthing is unreliable → Type D, after confirming MIE.
• Flammable gas or vapour below 0.14 mJ → Type C only, with verified earthing.
• Non-combustible bulk (clinker, sand, gravel) → Type A or B is sufficient and cheaper.

Six questions for the purchase order

Wording such as antistatic bag is not a specification. Put these six items in writing:

• Which edition of IEC 61340-4-4 does the test report cite? 2018 is current.
• What resistance was measured from fabric to the earth tab, and at what relative humidity? The standard tests at low humidity.
• How many earth tabs, and where are they placed?
• Which liner type is fitted (L1, L2, L3), and is it approved for this bag class?
• Is the value stated per bag or per production lot, and who signed the report?
• Does the class marking survive twelve months outdoors?

Matching the bag to the product

For fine carbon powders the class matters more than the fabric weight, because the risk is ignition rather than tearing. Our carbon black bags are built as documented Type C or Type D constructions, with earth tab count and liner stated on the spec sheet instead of left to interpretation.

Where the same product also ships in 25 kg units, the usual pairing is an antistatic-liner valve bag on the same filling line. For tonne loads lifted by crane or forklift, the FIBC bulk bag range covers 500–1,500 kg in both C and D options, standard or custom dimensions.

Send the product SDS and its measured MIE, and we will confirm class, liner and earthing requirement — in writing, with the standard edition cited — within 24 hours.