Type B FIBC are similar to Type A FIBC in that they are made from plain polypropylene or other non-conductive material. And like Type A bulk bags, Type B bulk bags do not have any mechanism for dissipating static electricity. The difference is that Type B bulk bags are made from materials that have a low breakdown voltage to prevent the occurrence of highly energetic, and dangerous propagating brush discharges (PBD).
There are two ways to achieve a low breakdown voltage in FIBC made from woven polypropylene. The first way is to use uncoated fabric. Although the polypropylene tapes have a high breakdown voltage, the air gaps in the weave of uncoated fabric has a low enough breakdown voltage to prevent PBD occurring. Clearly, Type B FIBC made from uncoated fabric cannot be used to package powders or other materials that produce fines that might leak through the uncoated fabric. The second way of achieving low breakdown voltage is to apply a very thin coating. However, because of the way coatings are applied to bulk bag fabrics, it is likely that holes and tears will occur in very thin coatings. Although a fabric with a very thin coating may have a low breakdown voltage, it is almost certainly incapable of providing the containment and protection required for packaging powders.
Although Type B FIBC can prevent PBD, they cannot be considered antistatic FIBC because they do not dissipate electrostatic charge and so normal brush discharges can still occur, which can ignite flammable solvent vapours. Antistatic bulk bags must have a consistent and reliable mechanism for dissipating static electricity. It is essential that only proven antistatic bulk bags with full static protection are used in any process that involves flammable solvents. In these situations CROHMIQ Static Protective Type D FIBC is the safe option.
Because Type B FIBC do not dissipate static electricity, there are consequences aside from the risks of incendiary discharges. Brush discharges from Type B FIBC can cause electrostatic shocks to operators. Whilst such shocks are not dangerous in themselves, they can be distracting and may lead to accidents. Another consequence of the build up of static electricity on Type B FIBC is that dust and other contaminants are attracted to the surface. This is clearly not desirable in food and pharmaceutical applications, and other applications where hygiene is critical. Electrostatic attraction can also make it difficult to fully empty Type B bulk bags. Several kilograms of powder can be left clinging to the inside of the bag. When the bulk bag is taken down and moved away from the emptying station, the residual powder may be dislodged and spill out. This again has an impact on hygiene within a factory and is detrimental to good house-keeping practice. Poor house-keeping and the build up of powder and dust has been implicated as a contributing factor in many combustible dust explosions.