An old nursery school just outside Horsens forms the focal point of Kristian Nissen’s bachelor project.

More specifically, it is the basement beneath the institution. It was originally built as a shelter to be used in the event of war – but it is by no means ready for occupation or operationally reliable should the sirens sound today.

“Right now, Denmark is counting the number of civil defence shelters it has, because there is no real overview of the condition they are in,” Kristian Nissen says of the motivation behind his project.

Since Russia launched its war in Ukraine, awareness of external threats has increased, and politically a new Ministry for Civil Protection and Emergency Preparedness has been established.

The threat level has also been raised several times since then, and Denmark is now facing more numerous and more serious threats than it has for many years. As a result, it is highly relevant to examine how the Danish emergency preparedness system can be updated to meet present-day needs.

Kristian Nissen therefore investigates how a basement from 1958 can be converted into a modern, fully functional civil defence shelter.

In his project, he looks to neighbouring countries such as Finland and Sweden which, due to their geographical location, have a very different level of focus on shelters – and entirely different requirements for them.

“They have sports halls and car parks that could be converted into shelters in the event of war. We simply don’t have that to the same extent in Denmark,” he explains, adding:

“Finland has a specific time requirement stating that shelters must be ready for use within 72 hours, whereas in Denmark the requirement is simply ‘within a reasonable timeframe’.”

Converting instead of building new

Unlike our neighbouring countries, shelters are not incorporated as an integrated part of buildings when new construction takes place in Denmark.

For this reason, Kristian Nissen illustrates how the basement in Horsens can be modernised so that it functions in a crisis situation, rather than examining what it would take to build new concrete shelters.

“It is more sustainable, and it is also cheaper to renovate instead of building from scratch,” he says.

In the project, he focuses on the installations in the space – that is, water, heating and ventilation systems – rather than the building structure itself.

“I base my work on the Swedish requirements in this area. They are further ahead and more up to date. Their regulations run to several hundred pages, whereas the Danish regulations are just 20 pages long,” he says.

Outdated regulations in Denmark

Despite increased political attention, Danish requirements for installations in civil defence shelters are outdated. The most recent regulations date back to 1993, and the threat landscape has changed many times since then.

Kristian Nissen therefore investigates which products could make the basement resilient to today’s threats. He examines solutions for water, heating and ventilation that comply with the Swedish regulations from 2024.

“If you want energy-efficient and sustainable operation in peacetime, you need two ventilation systems – and one that can operate in crisis situations,” he explains.

It is necessary to have a system capable of filtering air in the event of radioactive, chemical or biological attacks. This system must maintain positive air pressure inside the shelter so that contaminated air from outside cannot enter.

Currently, Danish requirements specify an air pressure of 30 pascals in shelters, whereas it should be 100 pascals according to a Finnish company whose products Kristian Nissen references in his project.

The ventilation system intended for wartime use is not particularly energy efficient because – for obvious reasons – safety requirements take precedence, and there is no focus on heat recovery.

Although it would be ideal to combine both functions into a single ventilation system, this is not currently possible. Such a product does not exist.

According to Kristian Nissen, installing two separate systems would most likely also be cheaper.

“There is, of course, an additional cost involved in installing two systems instead of one, but in the case of the nursery school it would pay for itself over 29 years, according to my calculations,” he explains.

In a larger shelter, the payback period would probably be even shorter.

A question of political will

Kristian Nissen cannot put an exact price on what it would cost to upgrade all Danish civil defence shelters, but he has analysed which measures are most important to implement.

The scenario in the bachelor project assumes that all shared utility supplies fail.

For that reason, it is essential to have an installed water tank filled with water, and lighting must also be considered.

“However, ventilation is the most critical installation during crisis operation, because the space must remain sealed and maintain a controlled positive pressure – and because people cannot survive very long without air,” Kristian Nissen explains.

He analysed air quality and CO₂ levels if either 32 or 64 people were placed in a 64 m² room equipped with the proposed ventilation system.

“People ‘just’ need to survive in the shelter if the alarm sounds. It won’t be a five-star hotel experience, but they wouldn’t die,” he says, adding:

“They would most likely experience headaches, nausea and feel somewhat sluggish because the air quality would be poorer than what we are used to. But they would survive.”

The conclusion of the project is therefore that Danish civil defence shelters can indeed be modernised and brought up to date – and with relatively simple measures. The principles applied to the basement in Horsens could easily be transferred to many other shelters across Denmark.

“It hasn’t been a political priority for many years, because we have enjoyed a long period of peace. But it is entirely possible to secure modern civil defence shelters, if the will is there,” he says.

The first step could be to take a look at Kristian Nissen’s bachelor project, which he will defend on 21 January. After that, he plans to continue on to a master’s degree and further specialise in Building Science and Technology.