Ünsa Electrostatic FIBCs
SAFE PROTECTION AGAINST IGNITION HAZARDS
Segregation procedures of the moving product particles during filling and emptying produce static electricity. When the FIBC is filled, the electric charge accumulates inside the FIBC on top of the product and may create a high electric field, that an ignitable discharge is possible. When filling and emptying the FIBC with a bulk product, a combustible dust arises inside the FIBC. Thus when filling and emptying the FIBC in hazardous areas with explosive atmospheres, a reliable protection against the risk of electrostatically induced ignitions is essential. Ünsa offers the entire range of protective measures for the safe handling of FIBCs in hazardous areas.
FIBC Types for Electrostatic Hazards
| TYPE A | FIBC without any protective measures against electrostatic charges. |
| TYPE B | FIBC with a breakdown voltage not exceeding 6 kV to prevent propagating discharges. Type B FIBCs can be used in the presence of combustible dusts with ignition energies > 3 mJ. |
| TYPE C | FIBC with interconnected electrostatic conductive film tapes and conductive loops and/or conductive tabs for grounding. The breakdown voltage does not exceed 6 kV. Type C FIBCs can be used in the presence of combustible dusts and in the presence of flammable gases or vapors with ignition energies ≥ 0,14 mJ. |
| TYPE D | FIBC made usually from non-conductive fabric containing conductive threads or filaments which are not interconnected. Charge dissipation occurs into the surrounding of the FIBC via corona discharge. Earthing of the Type D FIBC has only a minor effect on charge dissipation and is not required. Type D FIBCs can be used in the presence of combustible dusts and in the presence of flammable gases or vapors with ignition energies ≥ 0,14 mJ. |
Use of Different Types of FIBC
| Use of Different Types of FIBC | |||
| Bulk Product | Surroundings | ||
| MIE of dust (Minimum Ignition Energy) |
Non flammable atmosphere | Explosive dust atmosphere | Explosive gas and vapor atmosphere |
| MIE > 1000 mJ | A, B, C, D | B, C, D | C, D |
| 1000 mJ > MIE > 3 mJ | B, C, D | B, C, D | C, D |
| MIE < 3 mJ | C, D | C, D | C, D |
ÜNSA TYPE C
The dissipative Ünsa Type C FIBC which forms a reliable interconnected grid enclosing a maximum non-conductive area of 25 cm2. (e.g. 45 mm. mesh size) The FIBC has a resistance to ground at all points at the outside of R<108Ω . The breakdown voltage of the coated and uncoated fabric does not exceed 6 kV.
When filling and emptying, the Type C FIBC must be grounded. For the safe operation of the plant, Ünsa recommends double secured grounding via the conductive grounding tab and the conductive lifting loops.
The Type C FIBC can be fitted with a conductive inner liner. The conductive inner liner is in contact with the ground via the interwoven conducting filaments of the fabric and should not be removed from the FIBC in hazardous areas.
ÜNSA TYPE D
Under the trade name "HCD-Fabric®" Ünsa has developed a
High Corona Discharge Fabric. The Ünsa Type D FIBC made out of
HCD-Fabric® is certified by Wolfson Institute and Swiss Institute according to the IEC 61340-4-4 Standard. Ünsa Type D FIBC with
HCD-Fabric® is protected under patents in Europe, USA, Japan and Australia.
| European Patent No: | EP 1 411 007 |
| USA Patent No: | US 6,974,783 |
| Japan Patent No: | JP 2004-149222 |
| Australia Patent Appl. No: | 2003252786 |
The accredited electrostatic test laboratory of Ünsa has been established to carry out the below tests on FIBCs:
- Gas ignition
- Electrical breakdown voltage
- Electrical resistance
- Charge transfer
These test results are used for evaluating the electrostatic properties of FIBCs to be used in hazardous explosive atmospheres or for quality control purposes.
The laboratory can be conditioned between 60% RH and 20% RH, and 23°C via dehumidifier and air condition systems. All metal support frameworks, working platforms and any other conductors, including operators, within one meter of the tested FIBC are earthed, regardless of the FIBC being tested.
The tests are carried out according to IEC 61340-4-4 Standards. At least 200 ignition attempts on the test FIBC are made. The whole sequence of ignition attempts is made on each of the four walls of the test FIBC (50 ignition attempts on each wall). Additional attempts are made on any panel attached to the FIBC. After completing the ignition attempt no ignition should occur on the test FIBC. The tests are carried out with ethylene and enriched air mixture having a MIE of 0,14 mJ.
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| Type C | Type D without liner | Type D with liner |
WARNING
| Do not use FIBCs in the presence of flammable atmospheres with ignition energies < 0.14 mJ. |
| Do not use FIBCs in the presence of Hydrogen, Acetylene and Carbondisulfide (Group IIC according to EN 50014). |
| In order to prevent incendive spark discharges from the surface of Type B and D FIBC, it shall not become contaminated or coated with conductive material (e.g. water, grease or oil). |
| Additional precautions are necessary when a flammable gas or vapor atmosphere is present inside the FIBC (e.g. in case of wet solvent powders). |
| An important safe working practice with any type of FIBC in combustible dust and/ or vapor and gas atmospheres includes grounding of all conductive materials, equipment and personnel in and around the flammable surrounding. |
