Why Shipping Containers Are Overrated as Underground Shelters
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If You Believe Everything You Read On The Internet, Then You Probably Think A Buried Shipping Container Makes A Great Underground Shelter. Here’s Why That’s a Bad Idea.
The Internet is flush with articles about how easy it is to convert a shipping container into a shelter. The promise is that the main structure is already complete and all you have to do is bury it to protect yourself and your family from tornadoes, hurricanes, and even nuclear war.
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Common advice covers some level of ventilation, re-enforcement, and double-entry and exit points, but the downside and the dangers go well beyond standard assumptions.
The Fundamental Problem
Shipping containers are designed to hold cargo on ocean-going ships. They are designed to be structurally sound when stacked vertically. The structural integrity is defined by vertical re-enforcements that sustain weight at fixed points on the corners of the containers. And that’s where the problems begin when a container is buried underground.
Earth, Air, Fire, and Water
Shipping containers have very little structural integrity on their tops and sides. They are not designed to support weight on those surfaces. Only the corner beams support their weight when stacked. When a shipping container is buried, the force and weight of the surrounding ground on the top and sides will cause the container to slowly collapse and buckle.
Much advice is offered on how to support and re-enforce the tops and sides for thousands of dollars. But does it really make sense to spend so much to re-enforce a structure when you could construct a stronger structure from scratch?
Here are the facts:
A cubic yard of dirt weighs between 2,000 and 2,500 pounds, depending on the soil composition. A shipping container will quickly collapse under that pressure on the sides and top.
Think of it as an aluminum can. When you push down on the top of an aluminum can there is resistance. It has some relative, vertical integrity. If you squeeze the same can with two fingers it will quickly collapse. The design of a shipping container has similar characteristics.
An enclosed shipping container buried underground will obviously have no air circulation. The only solution is external venting, air circulation driven by fans, and above-ground ventilation pipes or tubes. This is a standard requirement for any underground shelter along with a hand-cranked or battery backup in case of power loss, but things can get complicated with a shipping container.
Leaks in the metal walls due to cracks, rust, or tears can allow gases to enter the container—from methane emitted by a septic field to propane from a ruptured propane tank after a tornado. Propane is heavier than air and hugs the ground. If it can find a way into a large hollow space like a buried and rusting shipping container, it will.
The whole idea of any shelter is to survive a disaster. Unfortunately, fire is a result of many disasters. Fires occur after earthquakes, tornadoes, hurricanes, civil unrest, and most definitely after a nuclear detonation.
It may seem that an underground shipping container would offer a safe haven, but shipping containers are often used by firefighters for training. A fire is built in and around the container, and the internal temperatures have been measured as high as 700 degrees Fahrenheit. A sustained fire raging above a shipping container can quickly turn that metal box into an oven.
Complicating matters are entry and exit points. If you are compelled to evacuate the container due to rising temperatures, all you’ll be doing is emerging into the inferno causing the heat. Entry and exit points are critical with any shelter, but just because you can get out of a shipping container surrounded by fire doesn’t mean you’ll survive once you emerge into the firestorm.
Any underground shelter has to deal with the constant threat of water. In fact, water may be the most insidious threat to any underground bunker.
- Water makes the surrounding earth heavier. Even a well-supported shipping container can buckle and collapse when the added weight of water combines with the weight of the surrounding soil.
- Water is relentless. It will always find a way to seep through cracks and crevices. Even a minute hole or gap in the metal of a shipping container can allow water to continually drain into the container. A sump pump can offer a solution, assuming it can keep up with the flow and that it also has a battery backup. Oh, and if that battery is contained in the shipping container, you’ll have fumes from sulfuric acid to ventilate as well.
- Water causes rust. Shipping containers are made out of metal. No matter how treated or painted the exterior may be, over time the paint will succumb, and the metal will rust. This will not only compromise the structural integrity but allow more water to flow into the container.
- Water leads to mold and mildew. Even when a shelter is effectively drained with a sump pump, the residual moisture can lead to the development of mold on surfaces. This is another problem for any underground shelter, but the potential for leaks in a shipping container makes it worse. Especially if black mold develops.
But Wait, There’s More
This gets back to the design and construction of shipping containers. They are made for cargo, not for people. As a result:
- They are sometimes painted with industrial paints on the exterior and interior that are not only toxic but potentially deadly with continued exposure in a confined space.
- Any wood in the container walls, ceiling, or floor is treated with water repellent chemicals that emit toxic fumes, especially in an enclosed space.
- Shipping containers are also treated with highly toxic fumigation sprays to kill and repel insects and rodents.
- Many shipping containers are made from something called “Corten steel.” This type of steel does not need to be painted but any nicks or scratches will quickly rust.
- The metal in a container combined with the surrounding earth can create a barrier to the transmission of any wireless signals for cell phones.
Are Shipping Containers Ever a Good Idea?
They can be if used above ground. They can be a quick and easy way to provide storage for farm equipment, tools, or general storage. Some people use them to park and store motorcycles, jet skis, snowmobiles, and recreational ATV’s.
Others have used above ground shipping containers as dedicated workshops for welding or woodworking. As far as using an above ground shipping container as a shelter, you have to ask yourself what you’re trying to shelter yourself from.
A tornado or hurricane can sweep away an above-ground shipping container as easily as a trailer in a trailer park. Strap it down all you want, but most trailers in trailer parks are strapped down as well, and many photos of past tornadoes have shown the devastation of too many trailer parks.
Underground Is Not the Solution
It’s when people start thinking of them as underground shelters that the problems begin.
With significant investment, lots of research, and due diligence, you may be able to safely convert a shipping container into an underground shelter. But there are still some lingering questions you have to ask yourself if that’s your plan.
- The average cost estimate that many people have reported for converting a shipping container into a shelter is in the range of $20,000 to $30,000. This includes the cost of the container, shipping and delivery, excavation of the ground, lifting and placement of the container, re-enforcement of the container, along with all of the things any underground shelter requires, from ventilation to dewatering systems.
- Many states and municipalities have assorted and strict building codes for everything from a deck to a barn, and especially for structures intended for human habitation. Those codes and the eventual inspections that will result might keep you a bit safer, but rest assured they will add to the total cost. And again, that’s true for any underground shelter, but some municipalities may simply prohibit the use of a buried shipping container as a shelter.
- Shipping containers have one entry and exit point—large doors on one end that swing open. A secondary exit will be required. But those large swinging doors will require that the container only be partially buried to allow the doors to open.
- Shipping containers are not bulletproof. If you’re concerned about looters and civil unrest, understand that the large doors will not protect you from gunfire.
- The entry and exit to any underground shelter can be blocked by debris after a disaster, whether it be natural or manmade. Those swinging doors on one end of the shipping container will only swing outward. That’s a bad design if debris has accumulated outside the doors. The same goes for any secondary hatch in the roof if it opens outward.
- They have a relatively short shelf-life. A concrete underground shelter will last longer than a buried, metal shipping container. Buried metal will eventually succumb to rust.
There Are Better Alternatives
If you feel the need to construct a dedicated underground shelter, there are better ways to spend your money than burying a shipping container. The best way is to hire a contractor with shelter building experience.
If you can only afford to do it yourself, do your homework. Depending on the nature of the disaster, you may have to spend significant time in your shelter. The key is to make sure it’s time and money well spent.
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