FIBC bulk bag electrostatic classification is governed by IEC 61340-4-4, and the choice between Type A, Type B, and Type C is decided by material minimum ignition energy, presence of flammable vapors, and whether a verified ground connection is feasible at every fill and discharge point [S3].
All three bag types share the same woven polypropylene substrate and the same 500-2,000 kg load range typical of standard flexible intermediate bulk containers, but the way each handles tribocharging during powder transfer is fundamentally different [S2]. Specifying the wrong type in a combustible-dust or flammable-vapor environment is a documented ignition-source risk, not a paperwork error [S1].
Type A FIBC: No Static Protection, Non-Hazardous Only
Type A FIBCs are constructed from plain-woven polypropylene and other non-conductive fabrics with no mechanism to dissipate or limit static charge generated as product moves across the inside surface during filling and discharge [S1][S4]. Because charge accumulates freely on the fabric, Type A bags are restricted to non-flammable products in environments where no flammable solvents, gases, or combustible dust clouds with minimum ignition energy of 1,000 mJ or less are present [S1].
Typical permitted uses include non-flammable agricultural products, construction aggregates, and general food-grade dry goods that are not combustible powders [S3]. Type A bags must not be specified where any ignitable atmosphere can form, since the bag itself can act as an isolated charged conductor and a propagating brush discharge source [S3][S4].
Type B FIBC: Low Breakdown Voltage, Combustible Dust Without Flammable Gas
Type B FIBCs share the non-conductive woven polypropylene substrate of Type A and likewise have no static-dissipative mechanism, but the fabric is specified with a low breakdown voltage that prevents propagating brush discharges across the bag wall [S1][S3][S6]. This is the critical physical difference: Type B does not ground charge away, it limits the energy a discharge can release if one occurs [S5][S9].
Because there is still no controlled path to ground, Type B bags are NOT approved for use in the presence of flammable vapors or gases, only in dry combustible dust environments where the dust MIE is sufficiently high and no flammable atmosphere is present [S3][S8]. The Type B envelope is narrower than procurement teams often assume; it is a dust-only solution, not a general-purpose flammable-atmosphere bag [S7].
Type C FIBC: Conductive Threads, Mandatory Verified Ground
Type C FIBCs are built from non-conductive woven polypropylene interwoven with conductive threads, typically in a grid pattern, that are tied to a verified earth ground at every fill and discharge operation [S1][S3][S4]. The conductive network provides a controlled path for static charge to leave the bag, so any discharge that occurs travels to ground rather than acting as an ignition source inside a flammable atmosphere [S6][S8].
Operationally, a Type C bag without a confirmed ground reverts to the hazard profile of a Type A bag, since an ungrounded conductive network is an isolated charged conductor, which is why every transfer step must include a grounding check [S3][S7]. Type C is the standard specification for Zone 1 and Zone 2 hazardous areas when a reliable ground can be established, including chemical processing, pharmaceutical powder handling, and mining applications with flammable atmospheres [S3][S7].
Decision Matrix: Type A vs Type B vs Type C on Six Criteria
The four FIBC types are routinely miscategorized in RFQs, so the following comparison is built from the IEC 61340-4-4 framework and the operational limits quoted across manufacturers and distributors [S3][S7][S8]:
Static control method: Type A, none; Type B, low breakdown voltage fabric limiting propagating brush discharge energy; Type C, interwoven conductive threads connected to earth ground [S1][S3][S6].
Grounding required: Type A, no; Type B, no; Type C, yes, mandatory verified ground at every operation, with loss of ground effectively reclassifying the bag as unsafe [S3][S7].
Safe in flammable gas or vapor atmosphere: Type A, no; Type B, no; Type C, yes when grounded [S3][S8].
Safe in combustible dust environments: Type A, only non-combustible dust; Type B, dry combustible dust without flammable gas; Type C, yes when grounded [S1][S3].
Typical load capacity and handling footprint: all three types share the standard 500-2,000 kg FIBC envelope and the same woven polypropylene substrate, so the differentiator is purely electrostatic [S2].
Failure mode if misapplied: Type A in flammable atmosphere becomes an ignition source; Type B in a flammable vapor atmosphere is not approved; Type C with broken ground link reverts to isolated-conductor hazard [S1][S3][S7].
Selection Rules: Who Each Type Is For and Who It Is Not For
Use Type A only when the product is non-flammable, the surrounding atmosphere contains no flammable vapors, gases, or combustible dust with MIE of 1,000 mJ or less, and no static-sensitive downstream process requires a grounded bag [S1][S3].
Use Type B when handling dry combustible powders in environments without flammable vapors or gases, and where the bag fabric's low breakdown voltage is sufficient to suppress propagating brush discharge risk, but do not substitute it for Type C in any flammable-gas atmosphere [S3][S7].
Use Type C when the operating area is classified as hazardous (Zone 1 or Zone 2) with flammable gases, vapors, or dust, and when a verified ground can be established and confirmed at every fill and discharge point, with documented operator checks per shift [S3][S7][S8].
Limitations, Failure Modes, and Sourcing Constraints
The most common failure mode in the field is not fabric failure but ground failure on a Type C bag: a broken ground clamp, a corroded grounding stud, or a lift truck without a confirmed ground path silently downgrades a Type C bag to a Type A hazard profile [S3][S7]. Periodic resistance testing of the conductive network, typically to a specified resistance-to-ground threshold per IEC 61340-4-4, is the only reliable way to keep a Type C bag in its certified class [S3].
Procurement should also confirm the bag is supplied with test certificates and traceability for the conductive-thread pattern, since non-conductive repairs, patches, or liners can break the conductive path and invalidate the Type C rating [S7]. For an overview of FIBC construction and how it relates to bulk bag selection in food, chemical, and mineral service, the IEC 61340-4-4 framework is the common reference cited across manufacturer technical datasheets [S3][S6].
When the operating environment cannot guarantee a verified ground on every transfer, a Type D bag using static-dissipative fabric and atmospheric corona discharge is the alternative specified in the same IEC 61340-4-4 framework, and is covered in the companion Type C vs Type D comparison published on 2026-05-21 [S7].
Trackable signals for the next planning cycle: confirm whether the site's hazardous-area classification has been re-validated since the last bag audit, verify that all Type C grounding clamps have documented resistance test records within the last 12 months, and review whether any new powder SKU has an MIE below the assumed 1,000 mJ threshold.
The underlying component specifications are covered under dry type transformer, and bag filter.
Background reading: Truck Scale Deck Corrosion: Salt Attack and Coating Selection.