Overview:
When filling or emptying bags with fine powders, static electricity can build up on the powder and on the walls of the bag. This can be dangerous when handling combustible materials or when there are flammable substances present nearby. To avoid this hazard, it is recommended to use anti-static bags when transporting hazardous materials.
Static electricity risks in explosive atmospheres:
What are the conditions/ingredients to create a fire and/or explosion?
There are 2 major conditions that can create hazardous fire or explosion in a supersacks.
Fire Triangle:
This is a situation where the supersacks are being loaded or unloaded in the vicinity of any fuel, ignition source, heat or any electrostatic discharge.
Dust Explosion Pentagon:
This is a situation where the supersacks are being loaded or unloaded in the vicinity high concentration dust cloud, combustible dust, confinement of dust or heat or any electrostatic discharge.
The types of discharge(s) that may occur due to the build-up of electrostatic charge on the FIBC include:
Brush discharges happen when there is a difference in potential between an insulating surface and a conductor. While there is no evidence that this could ignite dust, it could potentially ignite sensitive gas or vapor in the atmosphere. This can happen with all types of FIBC, but the energy is reduced in FIBC Type C by limiting the area between conducting threads and in FIBC Type D by reducing surface charge density.
PBD, or propagating brush discharge, occurs when two insulating materials with opposite electrical charges come into contact. This can be prevented in FIBCs, or flexible intermediate bulk containers, by using materials with a low breakdown voltage such as Type B.
A Spark Discharge is an electric current that flows between two conductors. This can be avoided by grounding all conductors, including FIBCs, support frames, tools, personnel, etc.
Cone (Bulking) Discharges are a potential ignition source for flammable atmospheres. They occur when powder is transferred from one vessel to another, and can require as much as 25mJ to ignite.
Brush Discharges from the surface of the powder after the completion of transfer operation. Brush discharges can ignite flammable atmospheres requiring up to about 3 – 5mJ to ignite.
Spark Discharges from:
– Metal sections of the powder transfer and storage system
– Conductive products in an insulating FIBC or vessel
– Ungrounded tools
– Ungrounded personnel
FIBC Types according to IEC 61340-4-4
Type A: No electrostatic protection, Capable to ignite a dust/air mixture.
Type B: Only liner is antistatic, fabric breakdown voltage < 6kV
Type C: Conductive fabric, Conductive or antistatic liner
Type D: Dissipative fabric and antistatic liner
Type C:
Type C according to IEC 61340-4-4: Type C industrial super sacks need to be earthed (grounded) to stop electrostatic risks. Type C industrial super sacks must be entirely made from conductive materials or must have fully interconnected conductive threads or tapes with particular patterns and particular distances between them.
For FIBCs constructed of multi-layer super sack material, at least one surface of the bulk super sacks shall have a resistance of less than 10^8 ohm. Type C FIBC labels or document pocket greater than 100 cm2 in area shall not be made from material with surface resistivity greater than 1,0 x10^12 Ohm. They need to be antistatic or conductive. The coating of a Type C fabric is insulating i.e. the surface resistivity is higher than 10^12 Ohm.
Therefore, ensure all parts of FIBC are stitched together either in a way that uncoated sides are connected face to face or ensure they are connected by using conductive film as a bridge.
For food compliance, they have to be coated or have an inner liner. Nonfood Type C bags can be uncoated.
Conductivity control of 100% of bulk super sacks is a critical quality control check to ensure all parts are connected.
Type D:
Type D according to IEC 61340-4-4: Type D FIBCs are constructed from super sack material fabrics with static dissipative threads and/or properties to control discharge incendivity. The inner liner (if needed) has to be L2 type.
When electrically isolated and subjected to “high charging” conditions, do not give rise to incentive static discharges.
Do not require grounding during use.
May be used where a flammable atmosphere is present.
Would pose ignition risk if FIBC surface is contaminated.
Conclusion:
Anti-static bulk bags are becoming increasingly popular because they not only save company’s money by preventing accidents, but they are also essential for the safety of employees who work on the ground. If you would like to learn more about how your company can benefit from using anti-static FIBCs, please contact us today!
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