Type D Big Bag (Static Protective)

Type D Big Bag: Static Protection Without Earthing

Type D big bag is made of static protective fabric that prevents sparks, brush discharges and propagating brush discharges without being earthed. Its electrostatic classification follows IEC 61340-4-4.

Quasi-conductive yarns woven into the fabric release the accumulated charge safely into the air through low-energy corona discharges.

Unlike a Type C big bag, it needs no earthing connection during use, which removes the risk of a forgotten or broken earth connection. It is widely used, especially in the US market.

Where Can It Be Used?

Under IEC 61340-4-4, a Type D big bag may be used in:

• Zones 21 and 22 (explosive dust atmospheres)
• Zones 1 and 2 (explosive gas atmospheres): gas groups IIA and IIB with a minimum ignition energy of 0.14 mJ or more
• Filling and discharge operations with charging currents of up to 3 µA

IEC 61340-4-4 does not cover Zones 0 and 20 or gas group IIC (e.g. hydrogen).

Rules for Use

• No earthing — The big bag is not connected to an earth bonding point
• Earth nearby conductors — All conductive objects within 1 m of the big bag (metal frames, hoses, personnel) must be earthed during filling and discharge
• Liner — Only Type L2 liners (surface resistivity 10⁹–10¹² Ω) may be used; liners with a conductive layer must not be used in a Type D big bag
• Cleanliness — Contamination such as water, oil or rust can impair the charge-dissipating properties of the fabric
• Label — Every Type D big bag carries the IEC 61340-4-4 number, the Type D designation, the static protection symbol and the note that it does not require earthing; markings such as “Type CD” or “Type D+” are not permitted

Type C or Type D?

Type C

• Conductive yarns carry the charge to the earth bonding point
• Earthing is mandatory
• Compatible liners: Type L1 or L2

Type D

• Static protective fabric dissipates the charge safely without earthing
• No earthing required
• Compatible liner: Type L2 only
• In gas atmospheres, limited to a minimum ignition energy of 0.14 mJ or more and charging currents of up to 3 µA

If reliable earthing is difficult at your site, or you want to remove the risk of earthing errors, Type D is suitable. If the minimum ignition energy of the gas is below 0.14 mJ or the charging current exceeds 3 µA, use Type C. The final choice is made in your site risk assessment.

How Is It Tested?

Under IEC 61340-4-4, a Type D big bag is filled with charged polypropylene pellets while at least 200 ignition attempts are made with an ethylene–air mixture with a minimum ignition energy of 0.14 mJ. A single ignition means the big bag does not qualify as Type D.

Tests are carried out at both 20% and 60% relative humidity. A type qualification certificate is normally valid for three years.