Type B FIBC bulk bags

What the Type B fabric is doing

Charge builds on polypropylene as powder flows across it. On plain fabric it can climb high enough across the bag wall to produce a propagating brush discharge, the most energetic kind of discharge a bag surface can give off, and strong enough to ignite many flammable dusts.

Type B fabric is made to break down at a low voltage, so the charge can't stack up to that level. It doesn't carry charge away to ground and it doesn't neutralize it. It simply stops the worst case from forming. Ordinary brush discharges can still happen, and those can ignite flammable vapours and gases, which is exactly why a Type B bag is limited to areas where none are present.

Think of it as a ceiling rather than a drain. The wall can't hold more than a modest charge before the fabric lets go of it locally, and that ceiling sits below the level a propagating brush discharge needs. Everything else around the bag, including people, drums, scoops and metal chutes, still has to be handled by your plant's own grounding and bonding.

Where the line is drawn

Three conditions have to hold together. The product is a dry powder. No flammable vapour or gas is present at filling, in transit inside the plant, or at discharge. Nothing on the line is relying on the bag to be grounded. Break any one of those and Type B is the wrong bag.

Solvent is the usual trap. A powder that left a dryer still damp with solvent, or a hopper vented near a solvent tank, changes the answer. Name IEC 61340-4-4 in your spec, read the maker's documents, and follow your site's hazardous-area assessment. We'll quote what that assessment calls for.

Changes on the line reopen the question. A new solvent wash, a different dryer, a product moved to another building, or a discharge point refitted to feed a reactor all mean the assessment should be looked at again before the next pallet is ordered.

Paperwork helps auditors as much as operators. Keep the assessment's bag requirement, the maker's test records and a copy of the label together in one file, somewhere purchasing can see it, so a reorder never drifts to a cheaper substitute.

Liners and other add-ons

A liner sits between the powder and the fabric, so it changes how charge behaves inside the bag. Don't drop a stock liner into a Type B bag on your own. Ask for a liner the maker has assessed with that bag, and keep the paperwork that says so.

Other parts follow the same rule: document pouches, labels and ties are part of the build the maker tested, so ask for them in the original order rather than adding them later.

Weather inside the plant plays a part as well, though not one you can lean on. A fill that seems quiet on a muggy afternoon can behave quite differently on a cold, dry morning. Plan for the dry day.

Choosing between B, C and D

Type C has conductive threads and a ground tab, and it only works when someone clips the cable on at both filling and discharge; unclipped, it's unsafe. Type D dissipates charge without any ground. Type B sits between plain fabric and those two and is the narrowest in use: dry powder, no vapour or gas.

Price is the wrong tiebreaker. The cheapest protected type the assessment allows is a fine choice; the cheapest one it doesn't allow is a hazard. Where two types are both acceptable, weigh the practical side: who connects cables, how many stations there are, and how often bags travel between buildings.

• Plain polypropylene, nothing flammable nearby: Type A
• Dry flammable powder, no flammable vapour or gas: Type B may fit
• Grounding is reliable and enforced at every station: Type C may fit
• No dependable ground, or vapour may be present: ask about Type D

Ordering and freight for Type B

Static-protected bags are quoted new only; a used bag's handling history can't be checked. They fold and bale like standard bags and travel on wrapped pallets, LTL or truckload. Send the powder, the assessment's answer, the spout sizes, the SWL and the ZIP, and we'll set up the load and confirm the day.

Receiving matters as much as ordering. Check that each bale carries the right label, that it reads Type B, and that the lot number matches the paperwork. Keep static-protected stock apart from plain bags in the warehouse, because a Type A bag grabbed by mistake looks almost identical on the rack.

Expect us to ask for the assessment's wording before we quote. It isn't red tape; it's how we make sure the bag landing on your dock is the one your engineer named.