Plain Bag - Low Breakdown Voltage
Prevents Propagating Brush Discharges
Do not use:
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 BigBulkBags 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.
|Inside FIBC||Atmosphere Surrounding FIBC|
|Non-Flammable Atmosphere||Explosive Dust Atmosphere||Explosive Gas or Vapour|
MIE > 1000 mJ
|A B C D||B C D||C D|
|MIE 3 mJ to 1000 mJ||B C D||B C D||C D|
|MIE < 3 mJ||C D||C D||C D|
|FIBC Type A||FIBC Type A are made from non-conductive fabric and provide no protection against static electricity.|
|FIBC Type B||FIBC Type B are made from non-conductive fabric. They differ from FIBC Type A in that the breakdown voltage through the fabric, including any coating, shall be low enough to prevent propagating brush discharges.Spark discharges may occur from the surface of FIBC Type B if they become contaminated or coated with conductive material (e.g. water, grease or oil). Precautions should be taken to avoid such contamination and to avoid conductive objects such as tools or metal clips being placed on the FIBC.|
|FIBC Type C||FIBC Type C are made entirely from conductive fabric or from a non-conductive fabric with interconnected conductive threads or filaments. The pattern of conductive threads or filaments is either:a grid enclosing an area of non-conductive fabric no greater than 25 cm2,
or a 20 mm stripe, in which case each thread or filament must be interconnected at two separate places (usually at both ends).
FIBC Type C must be provided with a grounding point to which all conductive panels, threads or filaments are electrically bonded. The resistance to the grounding point from anywhere on a conductive fabric and from conductive threads or filaments must be less than 108 ohm (updated to less than 107 ohm in the second edition of IEC 61340-4-4 – see below).
The lift loops of FIBC Type C must also contain conductive threads or filaments with a resistance to the grounding point of less than 108ohm (updated to less than 107 ohm in the second edition of IEC 61340-4-4 – see below).
FIBC Type C must also meet the breakdown voltage requirements of FIBC Type B.
In order to prevent spark discharges that might ignite a flammable or explosive atmosphere, it is essential that FIBC Type C are always securely grounded. A label should be attached to the FIBC indicating the position of the grounding point(s) and clearly stating the requirement for grounding. Ungrounded people may become charged through normal activity and could then discharge to ground when touching Type C FIBC. It is essential to follow normal safe practice and ensure that all conductors, including people, are grounded in the presence of flammable or explosive atmospheres.
|FIBC Type D||FIBC Type D are made from fabric that allows charge to be dissipated without being connected to ground. FIBC Type D fabrics usually contain conductive threads or filaments that dissipate charge safely into the atmosphere by low energy corona discharges. Some FIBC Type D have low resistivity coating that may reduce the risk of incendiary discharges.Grounding of FIBC Type D is not required.
To be qualified as safe for use in the presence of flammable or explosive atmospheres it must be first demonstrated that FIBC Type D do not produce incendiary discharges under realistic conditions.
Note: The conditions and procedures of test used to demonstrate the absence of incendiary discharges are specified in the draft IEC 61340-4-4.
FIBC Type D must also meet the breakdown voltage requirements of FIBC Type B.
Ungrounded conductors such a metal drums or people may become charged when positioned close to some FIBC Type D. It is essential to follow normal safe practice and ensure that all conductors are grounded in the presence of flammable or explosive atmospheres.
Spark discharges may occur from the surface of FIBC Type D if they become contaminated or coated with conductive material (e.g. water, grease or oil). Precautions should be taken to avoid such contamination and to avoid conductive objects such as tools or metal clips being placed on the FIBC.