At AZO, we primarily focus on unloading bulk bags, but we realize there are many other steps involved with transporting these FIBCs (Flexible Intermediate Bulk Containers). One of these steps is storage. There are proper and improper ways to store a super sack in your facility, as well as those situations when stacking bulk bags is not recommended.

This being said, “Should we stack our bulk bags?” is a question that still might come up when discussing bulk bag storage. There are some advantages to doing so. For one, it saves floor-space. It is also generally cheaper than investing in another specific storage method. In this blog, post we’ll briefly mention the alternative stacking method to stacking, explain the parameters for acceptable bag stacking and provide a bit of technical information to help explain why all bags are not meant to be stacked.

“Racking” is a stacking alternative that avoids certain risks

Let’s start with the risks involved with stacking: most notably, the safety hazard that is posed when multiple heavy sacks are stacked on top of one another, dependent upon one another to stay in place. Improperly stacked super sacks can fall, and even properly stacked bags could occasionally be put at risk due to other unrelated accidents. The other risk posed by bag stacking is not as critical for worker safety, but is related to product safety. 

Simply put, placing bags directly on the floor (or stacked upon each other) is not suitable for food commodities. Organizationally, bag stacking restrains FIFO (first in-first out) capability because the forklift cannot reach the oldest bags on the bottom of the pile. Prolonged storage leaves them vulnerable to infestations. The material can also expire or be easily influenced by environmental factors. At the end of the day, big bags that contain food-grade ingredients should not be stacked.

Rather, food-grade ingredients should be racked. Racking involves organizing the bags independently on racks and pallets. A separate rack location is needed for each bag. This does increase costs and space requirements. We will explain more about racking in another blog post, but racking offers an alternative when there are clear concerns with stacking bulk bags.

Bag stacking is acceptable under specific stacking methods 

Essentially, you should only stack FIBCs if they’re designed to be stacked. The ISO (international standards organization) has set a standard (ISO 21898) for fabric and whole bag integrity as a safety standard. There is an ISO specification that determines “SF” or “safety factor.” If an ISO-approved bag contains a label that rates the safety factor as “five .. one” this means that, as long as the bag is filled with product, this bag could theoretically withstand the weight of up to five bags on top of it. 

Big bags should be no more than triple stacked. Bags added to the stack should be handled in a manner that is safe for those working around it. Bags with a wider footprint improve both stackability and stability. (Baffle bags, which are specifically designed to retain their square shape, fit this description particularly well.)

After you assure that your bags can be stacked, it is still critical to stack them safely and correctly. The Flexible Intermediate Bulk Container Association (FIBCA) describes two types of stacking methods (“Pyramid” and “Supported” stacking) in these terms:

• Pyramid Stacking: Each bag above the first layer must sit on at least four lower bags. Each layer is subsequently tiered inwards forming a pyramid structure.
• Supported Stacking: Formed against two retaining walls of sufficient strength.

One notion of caution should be stated. The FIBCA warns to never approach or repair a damaged bag in the pile without first removing all bags on top of the broken bag. This damage would most likely be caused by a careless fork truck operator. A forklift fork can either puncture or tear the side of a bag, resulting in product spilling out of it. A floor-level bag with a large tear could then jeopardize the stability of stacked bags above it as well as the safety of nearby workers. It might be worthwhile at this point to describe the differences between the multitudes of super sacks available on the market.

The ISO (Test Method 21898) ensures the quality and strength of bulk bags and “manufacturing integrity”

Not every super sack is the same. The simple truth is that not all super sacks are stackable. How can you be sure that the bags in your facility are stackable? Again, ISO has set “ISO 21898” for fabric and whole bag integrity as a safety standard. This standard ensures a quality sack but many imported bags do not have this critical label.0

Each stacked FIBC should have an attached label with the following information: name and address of manufacturer, manufacturer’s reference, safe working load (with unit of measure) safety factor and the class of the FIBC (one-time of multiple use). An example of the safety factor would be “(5:1)” or “(6:1)” as we mentioned above.

If you’re buying material from a vendor that doesn’t include proper labeling, then the quality of the bag cannot be verified. If the label isn’t complete, then questions should be raised as well. To be sure, third-party ISO verification testing in the US is available through TEN-E labs in North Carolina, for example.

Stacking unlabeled or other poor quality bags can absolutely pose a safety threat to your warehouse. These shoddier bags will look the same but may not hold up as well while in storage. If you plan to stack your super sacks, first check for ISO approval. We also recommend confirming with your supplier what they recommend concerning stacking their bags. 

Ultimately, the seemingly simple question “should we stack our bulk bags?” turns out to be not so simple after all. The answer to that question will come down to a handful of other key questions. First, “what is in the bag?” “Is it ok to sit the bag on the floor?” “Is your super sack properly labeled?” Finally, “are your bags strong enough to stack?” Only after these basics have been addressed will you know if the advantages outweigh the risks associated with bag stacking.

Look for more information on “racking,” pallets and more tips on proper super stack storage in a future blog post here on bulkbagunloading.com. If you happen to be considering investing in a super sack unloading system or have any questions on how to help your plant and processes run smoothly in general, feel free to contact our AZO sales team. AZO has more than seven decades of experience in handling raw materials and shaping ingredient automation along the way.