Introduction
Regardless of your level of expertise, this article underscores the critical role that industrial or container desiccants play in shipping goods, whether by road, rail, or sea. Their primary purpose is to avert damage and minimize shipping losses.
You might be wondering, ‘What exactly is a desiccant?’ If that’s the case, take a breath! We’re here to provide a clear explanation in this article. Even if you’re a seasoned shipping professional looking to refresh your knowledge and gain some new insight into desiccants, we’ve got you covered.
** This article is provided for informational purposes only.
What does the word 'desiccant' mean?
Let’s dissect the term ‘desiccant.’ According to the dictionary, when used as a noun, it refers to a “desiccant substance or agent.” Admittedly, there’s not a lot of meat to that definition.
However, it raises another question: What exactly is a desiccant ‘substance’? We’ve all encountered those tiny packets labeled ‘desiccant’ inside pill bottles or other food packages, perhaps even in a bag of beef jerky. Perhaps you ignore them and eat the jerky bits, or maybe you thought it was a packet of extra salt?
Well, it’s definitely not salt. Perhaps the author of this article found that out the hard way one time.
Can’t confirm or deny that for you, but let’s not repeat past mistakes.
It’s the desiccant substance itself that makes a desiccant what it is. By definition, a desiccant substance is employed to maintain a state of “dryness” or “desiccation” within a specific environment.
Desiccant substances commonly come in pre-packaged forms (such as those found in the beef jerky packaging) and are solid materials designed to absorb moisture. There are also specialized liquid or gel desiccant substances that employ chemical bonding processes to soak up water molecules.
What are container desiccants?
As we’ve just covered, desiccants play a vital role in preserving ‘dryness,’ whether they’re safeguarding agricultural products, electronic equipment, pet food or granular substances like chemicals and medications.
Shipping professionals employ container desiccants as part of specialized shipping practices. These desiccants are strategically installed inside shipping containers to uphold dry conditions and absorb water molecules. In doing so, desiccants thwart a phenomenon known as ‘container rain.'
The Significance of Understanding Moisture and Container Rain
Freight insurance companies in the United States report staggering figures, suggesting that approximately 10% of transported goods in shipping containers are discarded due to moisture-induced damage. This percentage alone should raise eyebrows and prompt multiple readings to confirm accuracy. Such waste can significantly impact a company's expenses and delivery schedules.
One culprit behind this moisture damage phenomenon is what we call 'container rain.'
Container rain occurs when the relative humidity inside the container reaches 100% during transit. This results in the formation of water droplets that subsequently drip from the container's ceiling or walls onto the goods within. To effectively address the issue of container rain, it's crucial to understand its mechanics.
Let's delve into a brief science lesson. It's essential to grasp that warm air has a higher moisture-holding capacity than cold air. In simpler terms, warm air is more proficient at retaining moisture than cold air. Therefore, the air's moisture-holding ability diminishes when the air temperature decreases.
Shipping products across diverse climates can present formidable challenges for companies. Temperature fluctuations are common during various shipping stages, whether by road, rail, or sea. The most dangerous time for moisture accumulation is when the container is sitting still, for instance, a rail or shipping yard.
Now, consider this: if warm air experiences sufficient cooling during transport, such as when crossing vast oceans like the Atlantic or Pacific, the moisture in the air condenses. This is the moment when we encounter what's known as the 'dew point.'
The dew point is merely the temperature at which air cools to the end of becoming saturated with water vapor. If the cooling continues, the airborne water vapor transforms into liquid water, commonly called 'dew.' At this point, water droplets form on a cooler surface than the environment's air temperature when the dew point is reached.
This condensed water precisely gives rise to the problem we call 'container rain.' In a shipping container, the colder surface is typically the container's walls or ceiling. Consequently, these water droplets may cascade onto the cargo, resulting in costly damage.
The Moisture Absorber You Deserve… and Need
"Breaking news: Moisture wreaks havoc on shipping cargo, exacting a hefty toll on precious commodities! Who will ride to our rescue?"I
While this statement may carry a touch of drama, reminiscent of comic book sensationalism, the issue of container rain and moisture damage is no laughing matter.
Enter the unsung heroes of the shipping world—container desiccants. These remarkable saviors are strategically placed within shipping containers to maintain optimal dry conditions, battling the formidable foe of moisture damage.
Desiccants engage in a fierce battle against condensation, relentlessly absorbing moisture from the air.
They are the stalwart guardians, ensuring the container remains dry, even when confronted with fluctuating temperatures and shifting humidity levels.
Now, let's delve into the arsenal of substances employed in container desiccants. There exists a diverse array of desiccant materials, each possessing remarkable water-absorption powers.
What Sort of Substances are Used in Container Desiccants?
Among the most prevalent choices is silica gel, a porous form of silicon dioxide (silica) that harnesses the power of silicon and oxygen molecules to create a network of voids and pores. These pores in silica gel exhibit a potent chemical attraction to water molecules, rendering it a formidable water absorber.
However, the ranks of desiccant materials include other contenders, such as calcium sulfate (CaSO₄), charcoal, and calcium chloride (CaCl₂). Furthermore, there are eco-friendly desiccant materials that are 100% biodegradable, including substances like clay, coco peat, and even rock salts.
A Few Notes on Calcium Chloride vs Silica Gel
Now, let's turn our attention to the differences between two of the most popular desiccant materials, calcium chloride and silica gel, in the realm of desiccant supremacy.
These two contenders employ distinct methods to vanquish moisture from their surroundings.
Silica gel, as previously described, adeptly absorbs water molecules onto its surface. In contrast, calcium chloride, an inorganic compound, starts as a white crystalline solid at room temperature but readily dissolves in water.
While traditionally known for de-icing and road surfacing, calcium chloride has also earned its place as a desiccant due to its "hygroscopic" and "deliquescent" properties. These scientific terms essentially mean that calcium chloride absorbs moisture like silica gel, but remains in a liquid state with a binding agent.
What are the Differences of Both Compounds?
Silica gel is efficient at regular temperatures but may lose some of its absorption prowess at higher temperatures. Conversely, calcium chloride maintains robust absorption capabilities, particularly in higher humidity and temperature conditions.
Calcium chloride boasts a lengthier absorption period and a greater capacity to contain water molecules.
Ultimately, when discussing the two together, calcium chloride is above and beyond the better performing desiccant material. Consulting with a sales person when purchasing desiccants is a good practice to understand what type of material you’re getting.
What about their absorption performance?
Speaking of absorption performance, desiccant bags designed for shipping containers typically contain a substance that greedily soaks up humidity from the surrounding air. The effectiveness of these formulas varies, depending on the desiccant material.
For instance, silica gel desiccants absorb approximately 40% of their bag weight. In simpler terms, a 2 kg bag can absorb roughly 800 g of water. Conversely, desiccant materials like calcium chloride exhibit remarkable prowess, absorbing up to and exceeding 300% of their weight. A 2 kg bag of calcium chloride can absorb 6-10 kg of water.
This astounding capability prompts many shippers to opt for calcium chloride bags, owing to their status as the highest absorbers available. Biodegradable mixtures of calcium chloride and clay, capable of absorbing roughly 100% of its weight and providing a 1:1 ratio of performance.
However, a more potent absorber like calcium chloride should be your trusted ally if you embark on a longer journey through diverse climates marked by significant temperature and humidity fluctuations.
More Desiccant Advantages and Installation Methods
Due to many factors a loaded container becomes its own ecosystem. Condensation will occur on surfaces inside the container. Installing desiccants in the container prevents condensation from occurring by absorbing water molecules that would accumulate on the container walls, ceiling or cargo,
In terms of installing desiccants, there are many ways to go about this. Almost all shipping containers contain a corrugated wall design and have lashing rings that run down the length of the container for securing points for shipping liners or hook-up points to strap more extensive materials in place.
These indentations and lashing rings are also great spots to hang up desiccants. Another point to touch on is how simple container desiccants are to use. Here’s a breakdown:
Step 1: Walk into the container and hang the desiccant on the lashing ring against the wall.
That’s how easy it is. Not even kidding.
However, desiccants in shipping containers can come in many forms. Several bags can be assembled on a pole and hung on a lashing ring. These pole bag types are long and slot into the groove along the wall so it doesn’t take up any space for products to be moved into the container afterward.
Other types of desiccants are individual, larger bags sewn to a hook or strap that sit near the container ceiling on a lashing ring. Others can be desiccant-filled bags that sit along the container floor to combat any moisture that condenses and pools at the bottom of a container.
Even specific desiccant-infused paint or sprays can be applied to the container ceiling, floor and walls that absorb moisture. These desiccant compounds are primarily for automotive work but are also found in commercial-grade options.
What Sizes of Desiccant Bag are Available?
Sizes and styles of desiccant bags for shipping containers can vary in dimension, material capacity, and even practicality if the bag needs to fit within the wall groove for a tight load.
As discussed, some desiccants come in a vertical line and hang on an attached pole that keeps the bags suspended when hung in the air. These bags, called “pole” or sometimes “magnum” desiccants, are designed for tightly packed containers and fit vertically in the container’s corrugated walls.
The “cargo bag” or “piccolo bag” desiccants come as a single bag with a plastic hook or strap for suspending it. These are for bulk-loaded or pallet-loaded containers that permit room at the top for the desiccant to hang on a lashing ring.
Container desiccants can come in bag sizes ranging from 100 - 300 g at the smallest and up to 1.5 kg or even 2 kg bags. These weights refer to the mass of the desiccant material inside them before use and not the final weight.
How Much Desiccant or How Many Desiccants Do I Need?
It’s vital that when using a desiccant, you’re using the right amount. That’s very vague advice, so how much is enough? It depends on a few different factors, ultimately.
What desiccant material are you using and what’s the absorption rate?
What’s the climate and relative humidity of the transport location?
How long of a distance is it to transport it?
How large is the desiccant package and what’s the saturation point?
These are all great questions to ask when trying to get the correct amount of desiccant in your shipment. However, many shippers argue that the best practice is calculating by going off of the cubic feet of the container and the type of material used to find the correct amount for any given shipment.
In some cases, providers can more accurately predict how much desiccant is truly needed through data loggers that are inserted inside containers. These devices record humidity levels in the container throughout a given journey, every hour. This can help paint a very accurate picture of how many desiccants you need. Another good customer practice is to ask your desiccant provider on what test methods they offer.
The MIL-D Specification
An excellent place to start without knowing the answers to this question is learning something called 'desiccant units.' The U.S. military, for instance, uses a specification called the "MIL-D-3464," which determines how much of a desiccant is needed to absorb a specific amount of water vapor to prevent corrosion and mildew in different conditions.
The 'MIL-D' spec determines the 'desiccant unit' by testing how much material is required in two different test formats:
It's important to note that these measurements are calculated under ideal conditions, but they remain a good guideline for determining the quantity of desiccant needed.
For instance, the MIL-D spec defines that it takes 26g of silica gel to absorb the required water vapor under the above conditions. A more straightforward way of looking at this would be to say that, '26g of silica gel = 1 desiccant unit of silica gel.'
How much silica gel would we need for a standard 20’ shipping container under that specification?
Using the above example of 26 g of silica gel as one desiccant unit, we can now look at the average of how much one desiccant unit is needed to cover in terms of cubic feet. A standard 20' container is typically: (19'4" long) and (7'9") wide by (7'10") high.
Let's say our container is precisely that. Those measurements give us 146 ft² of floor space and 1,172 ft³ for total volume in the container. Now, we need to see how many desiccant units are required to perform in an area of that size adequately.
The MIL-D spec states, "...1.2 units of desiccant is needed for 1 ft³ of air volume to be considered best practice."
With this in mind, we must multiply the total container volume (1,172 ft³) by 1.2 desiccant units. That gives us a total of 1,406.4 desiccant units. Regarding the amount of silica gel, if one desiccant of silica gel unit is 26 g, we need 36,566.4 g for the container to provide adequate performance.
Now, don't panic. That's a considerable number, but there's no need to grab a shovel and look for a mountain of silica gel. We need to consider the scale of how many grams that is in the packaging of shipping desiccants. First off, grams (g) are a small unit. It's only about 37 kg (82 lbs) of silica gel for one 20' container, roughly the size of a large emperor penguin. Fun fact!
With that perspective, we know that shipping desiccants can come in different quantities. There are smaller desiccants, around 100 g or even much smaller than that; some can go as large as 1.5 kg or 2 kg per bag.
If you're dealing with a large space like a 20' container, it's safe to assume you'll use a heavier desiccant bag. Let's say you are calculating to use 1.5 kg silica gel desiccants in your container. Taking (37 kg) and dividing it by (1.5 kg per bag) we get a total of 24.667.
Let's round up to be safe, and now we know that for a standard 20' container using 1.5 kg silica gel desiccant bags, you need at least 25 bags to hang inside the container to meet the best practice using the MIL-D spec.
One last thing to keep in mind is that the MIL-D spec is also just one example of measurement. Talking to your sales person will give a much more specific answer to how much desiccant you need.
What about calcium chloride desiccants in this scenario?
An important thing to keep in mind is that the above scenario was for one type of desiccant material. Some manufacturers say you need ten times more silica gel than calcium chloride to get the same coverage.
That knowledge might push shippers to use calcium chloride instead of silica gel desiccants. Instead of 37 kg of silica gel, you may only need about 4 kg of calcium chloride.
Similar desiccant bag sizes apply for calcium chloride desiccants, so you may only need a fraction of the amount of bags you would need otherwise. Using 1.5 kg calcium chloride desiccants and needing only 4 kg of material, you can get away with only four bags to cover the MIL-D specification.
Other Factors for Calculating the Amount of Desiccant Needed
To summarize, calculating the amount of desiccant required is always dependent on a few factors. These are crucial for calculating and understanding the situation for optimal moisture control. The factors are:
Container Size: Depending on how large the container you’re using, it depends on the air volume inside— consequently, the larger the space, the more moisture that can be present. A good rule of thumb is that the larger the container, the more desiccant is needed.
Cargo Type: Different cargo can have different sensitivities to moisture. Electronics and metals are susceptible to moisture and may require more desiccants than average. In contrast, textiles and some food products might be less sensitive.
Packaging: The materials used in packaging can also determine the quantity of desiccants used. Plastics are less permeable to moisture and, therefore, require less desiccants, whereas package materials like cardboard might need more desiccants.
Duration: The longer the shipping trip, the longer the cargo is exposed to potential moisture. If your shipment will be going 60+ days on a cargo ship, using more desiccant than what’s required would be beneficial.
Climate: Whatever climate you ship your products through may dictate the amount of desiccant applied in the container. If the route involves a significant change in temperature and humidity levels or an overly humid region, more desiccants may be essential.
Final Overview
Moisture is everywhere in our atmosphere in different quantities, depending on where you are. Because of this variable, shipping goods through various climates can have costly consequences if you’re not prepared for the potential factor of moisture damage.
Therefore, desiccants are a valuable commodity to have for any shipping company. Shipping desiccants used in any make or model of container help absorb that moisture to help get your goods to their destination in excellent condition and ideally undamaged.
Desiccants safeguard all products, including agriculture commodities, pet food, chemical powders, or other packaged commodities. Understanding a little of the science behind container rain and knowing how much of which desiccant material you need will go a long way in reducing the risk of loss and optimizing your shipping logistics.
In a world where every percentage point in shipping losses matters, the value of the moisture-absorbing super bags we call desiccants cannot be overstated.
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