Could humanity survive living in bunkers?

When you start looking through the news it doesn’t take long to find a story about a possible world war or some kind of extraterrestrial threat like an asteroid on a collision course. Even without an initial triggering factor, there is a very real chance that something bad will happen naturally to our planet and humanity will be forced to live in a protected survival environment away from whatever it is that has made the environment uninhabitable.

The last time this happened naturally was 66 million years ago when an asteroid hit the earth and wiped out the dinosaurs, but it wasn’t the impact itself that killed them. The collision threw a huge amount of debris into the atmosphere, and the shockwave was so powerful that it triggered most of the volcanoes on Earth which all erupted at the same time. The sky was so thick with ash that it blocked out the sun for an estimated two years, causing all plant life to die along with the animals that depended on them.

The chance of an asteroid of the same size hitting the Earth is very small, but there is a much higher chance that someone will press the red button and set off a bout of nuclear warfare. Whatever the reason could be, the question is “Would it be possible for humanity to survive underground for an extended period?”

How long can you survive in a bunker?

The average bunker that is designed for more than a single night stay, like a bomb shelter for example, is only suitable to be lived in for no more than two weeks. The problem comes with supplies and sanity, both of which have a huge amount of individual factors that determine the length of time you can stay underground. The size of the bunker isn’t as important as what’s in it, but with so many different types and shapes of bunkers, it’s easier to just go through the factors that will determine the amount of time you can stay underground.

Power supply

A 15kw generator will use about 1 gallon of fuel per hour and be able to power a bunker that can house up to 20 people. This will require a schedule for the use of high-energy-consuming items like electric showers so the system doesn’t trip, but would indeed be possible. A 10,000-gallon fuel tank would last for just over 400 days at this rate but would take up a large amount of space and cost a great deal. The other problem with liquid fuel is that it goes bad and both diesel and petrol go off after about one year, so even if you could store more it wouldn’t do any good.

The most advanced option would be a nuclear battery, such as the type used on aircraft carriers which can provide power for over 20 years. The chances of getting hold of one of these would be close to impossible if you weren’t building a bunker for high-ranking government officials. Surface-based renewable energy sources would be a bad choice because they probably wouldn’t last for very long and would require people to go outside to maintain them, which might not be an option depending on the type of apocalypse.

The only option for safe and consistent power would have to come from flowing water, which could be re-directed from a nearby river and channeled underground to a power room in the bunker. The water would flow through a series of vortex turbines and then back outside again to rejoin the main flow, and if the river didn’t dry up in the summer it would have no reason to stop producing power. The water could also be collected and run through a filtration system to provide unlimited drinking water, with the waste going back into the main flow and out of the bunker.

(A design for a billionaires bunker, but with the amount of people and supplies they seem to have, they’d be lucky to still be alive after 12 months)

Oxygen

It would be impossible to either store enough oxygen in tanks or build a system that could clean the air to a degree that would be safe to live in for a long time. Air would have to be pumped in from outside and this would require it going through a series of carbon filters or another purification method. Without power, you wouldn’t have time to die of thirst because the air would become too thick with CO2 to survive.

Water

Without a source of fresh water, you could last for as long as your water tanks held out and didn’t get contaminated. The average person will drink around 4 pints per day, and require another 4 in a bunker setting for cleaning and cooking. This means that a 10,000-gallon water tank will last 20 people for 500 days, but this would mean very few showers and having to flush the toilet with waste cleaning water. Fortunately, it would be possible to dig a well or pump system within the bunker in the ground below, and bunkers are also known to have problems with collecting water around their lowest layers which would be collected and purified.

Food

Canned food usually doesn’t last for more than five years before it either starts to go bad or rapidly loses its nutritional value. Dried goods like peas and beans can last for ten years and dehydrated food lasts for about the same amount of time, but after this, you’d starve, unless you had a lot of money. The best type of food you can have with a long-term bunker is freeze-dried food because it offers the most variety and can last for 25 years.

A standard pallet filled up with packs of freeze-dried food to a height of 6 feet can provide 2,000 calories for one person for two years. 10 pallets will last a group of 20 people for a whole year, so you’d only need 250 pallets of food to feed everyone for 25 years. This would take up a huge amount of space but large storage rooms could be specifically built to accommodate them, but the cost for all this food would be several million.

(A classic fallout-style shelter designed for no more than a couple of weeks)

Sanity

Have you ever been trapped underground with the knowledge that you can’t go back to the surface without dying? me neither, but this will constantly be in the back of the minds of anyone trapped in this situation. The smaller the bunker and the more people in it, the faster someone will lose their mind and do something stupid. Even if everyone has their own personal space, there is also the mental factor of their surroundings and not being able to see the sky or feel the warmth of the sun.

Mildly claustrophobic people will have this fear amplified upon the realization that they have to stay inside, and anyone who suffers from it badly will become a nervous wreck. People will also need a recreational area that imitates the outdoors, and the entire bunker would have to be themed so it looks as “outside” as possible.

Health

The range of nutrients that could be gained from freeze-dried food would be sufficient to support someone for many years, but people could easily develop a deficiency if they didn’t stick to a careful diet. Vitamin D bulbs would have to be used because this would be the only way people could access it, but food and light would be the only way to get fresh vitamins and nutrients. Most supplements last for no more than two years, so stocking them for a long stay would be a waste of time.

Medicine would also go off over time and there are only so many things you can make while trapped in a bunker. Anyone requiring a constantly prescribed medicine like insulin wouldn’t last longer than their stockpile held out or went off, and the smallest of injuries or illnesses in a bunker could end very badly. The bunker would also have to have an area dedicated to physical exercise, as there wouldn’t be anything to do down there and people could get unhealthy through inactivity.

What’s the longest humans could survive underground?

If cost and availability of materials weren’t a factor, then in theory it would be possible for humans to survive underground until any necessary equipment they had broke down. The only way to power a facility for longer than 25 years would be with a source of water flowing through a power room, or by having spare nuclear batteries you could activate and swap over every 20 years. If the needs for power and water were met, the biggest challenge would be the production of food and building the bunker in the first place.

If people needed to grow their own food down there then it would have to be big, really big. You would need about one acre of internal bunker space per person to have enough room to feed someone, provide a living space, and store all of the things they’ll need.

The city of New York covers an area of 193,700 acres, so if you built a bunker the same size as the city, you could house just as many people. This is about 1/25th of 1% of the country’s population so even if you had a few trillion dollars spare, you’d still be far from being able to save everyone.