Flexible intermediate bulk containers (FIBCs), sometimes known as bulk bags, are widely used in the chemicals, pharmaceuticals, food, agriculture and other chemical process industries (CPI) sectors, to transport and store dry, flowable bulk-solid materials, such as granules, powders, grains, clays, cement, resins and others. This one-page reference provides basic information on FIBCs to aid in their selection and use.
FIBC bag construction
Most FIBCs in use in the CPI are made of polypropylene extruded in threads or ribbons and interwoven in a longitudinal-and-transverse pattern. When filled, FIBCs can be handled by forklift trucks, cranes or hoists, and are designed to be lifted from the top by means of permanently attached lift loops, sleeves or stevedore straps.
Generally, FIBCs in use at industrial sites are one of the following types:
U-panel. U-panel bags have one panel forming two opposite sides and the bottom, creating a “U” shape.
Circular. A circular bag (also known as a tubular bag) is made from fabric woven on a circular loom that is then cut to the proper length for a specified bag height. This eliminates the vertical seams on each of the bag’s sides.
Four-panel. Four separate pieces of fabric are sewn together to create the body of the bag.
Baffle. In a baffle bag, pieces of fabric or other material are sewn across each corner of a tubular or four-panel bag to help stabilize the load and more efficiently utilize storage or shipping space.
Linings. FIBCs can be used with or without liners. Two common liner types are form-fit and tubular. Form-fit liners will allow improved filling and complete discharging of product. Tubular liners are straight cylinders that may have one end heat-sealed.
FIBC selection and use
FIBCs are lightweight (5–7 lbs), offering a low package-to-product weight ratio and the ability to hold one metric ton of product. With a standard filled diameter of 45–48 in., FIBCs are designed to fit two across in a truck or a shipping container, although specially configured containers are available (Figure 1).
To ensure that an FIBC will meet the requirements for handling a specific product, users should seek to answer the following questions on product details:
• What is the product’s bulk density (lbs/ft3 or kg/m3)?
• What is the safe working load (SWL; the amount of load that a FIBC is designed to carry) and the net fill weight needed per FIBC?
• Is the product considered a hazardous material or dangerous good?
• Does the FIBC need to meet pharmaceutical or food-safety requirements?
• What is the product’s mesh size (particle size)?
• What is the product’s moisture content?
• Are there special barrier needs (is the product hydroscopic, for example)?
• What are the product’s flow characteristics (free-flowing, dust-forming, bridging, static buildup)?
• What is the filling temperature?
• What are the product’s sensitivities to agglomeration, clumping, mechanical deformation, vibration?
Handling FIBCs involves safety considerations, including the following:
Load. The SWL is determined by the design of the FIBC, along with the sewing method used and the strength of the fabric.
Antistatic. FIBCs made from plain woven polypropylene and other non-conductive materials (Type A FIBCs) offer no static protection. Type B FIBCs are made from plain woven polypropylene fabrics that have a low breakdown voltage to prevent the occurrence of highly energetic propagating brush discharges that can ignite a dust-air mixture, according to ABC Polymer Industries, a maker of FIBCs. However, Type B FIBCs do not have any mechanism for dissipating static electricity. Type C FIBCs are made from non-conductive polypropylene fabrics interwoven with conducting threads, normally sewn in a grid pattern, that connect the bag to ground via a grounding point. Type D FIBCs are made from antistatic and static-dissipative fabrics that are designed to safely prevent the occurrence of incendiary sparks, brush discharges and propagating brush discharges without the need for a connection from the bulk bag to the ground. Type D FIBCs are designed to safely package combustible products and to handle products in combustible and flammable environments.
Stacking. FIBCs should only be stacked if they are designed to be stacked, if their stability is assured and if they are stacked using a “pyramid” or “supported” stacking method. In pyramid stacking, each bag above the first layer must sit on at least four lower bags. Each layer is subsequently tiered inward, forming a pyramid structure. Supported stacking refers to placing FIBCs against two retaining walls of sufficient strength.
Filling and unloading. Filling and discharging options are shaped by the filling method (conveyer, gravity, bulk bag filler), clearance, desired fill rate, discharge method (gravity, screw, conveyor, bottom cut, full dump) and whether or not controlled discharge is required, as well as whether bag handling is available.
1. ABC Polymer Industries LLC, “What are the differences between Types A, B, C and D FIBC fabrics, Newsroom, Dec. 10, 2014, www.abcpolymerindustries.com, accessed Dec. 2021.
2. Flexible Intermediate Bulk Container Association, Resource Center, www.fibca.com, accessed Dec. 2021.
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