Executive summary
Finland and Switzerland both maintain mature civil-defence shelter systems, but they expose different design logics.
Finland’s framework is unusually explicit in legislation and decrees. It defines when a shelter is required, how the protected floor area is calculated, the shelter class by protected area, pressure-wave design loads for S1, S2 and rock shelters, minimum structural thicknesses, ventilation rates, minimum overpressure, maintenance intervals and equipment design life.
Switzerland operates a highly standardised federal shelter system built around a reinforced-concrete protective shell, blast-resistant closures, emergency egress, protective ventilation, gas filtration, overpressure/explosion-protection valves and tested components. Federal technical instructions remain central to the system, and the country continues to treat shelter infrastructure as a long-life national asset that requires inspection, renewal and readiness.
The comparison is most useful when read as two mature answers to the same project question:
How is a protection objective translated into a repeatable building system that can be designed, approved, maintained and activated years after construction?
1. Regulatory architecture
Finland
Chapter 11 of the Finnish Rescue Act governs civil-defence shelters. Section 71 establishes the shelter-construction duty for qualifying new buildings. A shelter is generally required when a building or building group on the same plot has at least 1,200 m² of floor area and is used for living, working or otherwise permanent occupancy. For industrial, production, storage and assembly buildings, the threshold is 1,500 m², subject to the statutory conditions and exceptions.
Section 74 defines the protective purpose. The shelter must protect occupants against weapon effects, building collapse, ionising radiation and toxic substances, while temperature, air quality and hygienic conditions must remain adequate for the intended use.
The legal framework is layered:
- Rescue Act 379/2011: obligation, purpose, readiness and authority framework.
- Government Decree 408/2011: size, location, shelter class, structural loads and structural minimums.
- Ministry of the Interior Decree 506/2011: rooms, ventilation, water, sanitation, electricity, communications, maintenance and penetrations.
- Government Decree 409/2011: shelter devices, markings, environmental resistance, product information and design life.
The Finnish system makes the shelter a predictable building requirement rather than an exceptional specialist add-on. Once a project crosses the statutory trigger, the designer can identify the need early enough to coordinate the shelter with structure, basement planning, circulation, technical rooms, ventilation routes and normal-time use.
Switzerland
The Swiss Federal Office for Civil Protection (FOCP/BABS) describes a national objective of a shelter place for every inhabitant. Around 370,000 private and public shelters provide places for essentially the whole population, while local gaps remain.
Shelter construction remains an active obligation in areas where municipalities have insufficient shelter places. BABS explains that owners constructing residential buildings may be required to build, equip and maintain a shelter, while compensation payments can apply where a shelter is not built because of technical reasons or sufficient local coverage.
The Swiss system is defined not only by law but by a visible federal technical-document architecture. BABS publishes technical instructions for mandatory shelters, special shelters and protective structures, together with technical specifications for ventilation units, NBC filters, overpressure valves, explosion-protection valves and related components.
The Swiss model is strongly system-oriented. The protective shell, closures, ventilation chain, equipment and inspection regime are treated as one standardised protective infrastructure package. For project teams, this means component approval, installation interfaces and lifecycle requirements matter as much as the existence of the room itself.
2. Shelter sizing, classification and location
Finland
Government Decree 408/2011 requires the actual protected area to be at least:
- 2% of total floor area for the general building categories covered by the shelter obligation;
- 1% of floor area for shop, industrial, production, storage and assembly buildings;
- minimum 20 m² of actual protected area.
Where sizing is permitted on the basis of average occupants, the protected area is 0.75 m² per person unless a larger area is needed for a particular reason.
Shelter class is determined by actual protected area:
| Actual protected area | Class |
|---|---|
| up to 135 m² | S1 reinforced-concrete shelter |
| up to 900 m² | S2 reinforced-concrete shelter |
| up to 4,500 m² | rock shelter |
Since the 2018 amendment, a shelter may generally be located up to 500 m from the building it serves, with a possibility for a competent authority to allow a more distant common shelter in specific threat-based circumstances.
The Finnish sizing rule ties protection directly to ordinary building metrics. The result is architecturally important: the shelter area can be estimated during early space planning, before detailed engineering begins.
Switzerland
Swiss shelters range from very small private shelters to shelters for hundreds or more occupants. BABS states that the same basic principles apply regardless of size because the system is largely standardised.
The federal shelter brochure describes a minimum floor area of approximately 1 m² per occupant and a volume of 2.5 m³ per occupant for the shelters it describes.
BABS also increasingly favours larger shelters for economic and organisational reasons, while many private shelters still serve roughly 5 and 50 people.
Finland connects shelter class to protected floor area. Switzerland presents a more standardised family of shelter solutions whose scale can vary considerably while retaining the same core protection principles.
3. Protection objective and threat basis
Finland
The Rescue Act sets the high-level protection objective: weapon effects, building collapse, ionising radiation and toxic substances.
Government Decree 408/2011 then translates one part of that objective into explicit pressure-wave structural design loads:
- S1 reinforced concrete: 100 kPa
- S2 reinforced concrete: 200 kPa
- rock shelter: 300 kPa
These are statutory design loads. The cited clause itself does not identify them as incident pressure or reflected pressure.
Pressure terminology note
Incident pressure is the pressure in the propagating wave before it interacts with a major surface. Reflected pressure is the amplified pressure that can occur when that wave strikes a surface. The relationship depends on wave intensity and angle of incidence.
For this research, these concepts are used only to explain why a bare pressure number requires a clear reference condition. The Finnish statutory values above are not re-labelled as incident or reflected pressure unless the applicable design document explicitly does so.
Switzerland
BABS describes Swiss shelters as primarily intended for armed conflict and designed to provide basic protection against modern weapon effects, including NBC agents and near hits from conventional weapons.
The TWP 1984 technical instruction repeatedly describes the standard mandatory shelter as a 1-bar shelter. The same document explains the protective contribution of underground location, the reinforced-concrete shell, building mass, controlled openings and filtration.
Both systems recognise blast/weapon effects, but the public documentation exposes the design philosophy differently. Finland places explicit pressure classes directly in decree. Switzerland uses a long-established standard shelter concept supported by federal technical instructions and standardised components.
4. Structural shell
Finland
Government Decree 408/2011 specifies minimum reinforced-concrete thicknesses.
For an S1 shelter:
- external walls and roof: at least 300 mm reinforced concrete;
- floor, load-bearing internal reinforced-concrete walls, columns and intermediate slab in a two-storey shelter: at least 150 mm.
For an S2 shelter:
- external walls and roof: at least 400 mm reinforced concrete;
- other structural minimums increase accordingly.
Rock shelters are designed on rock-mechanical principles, and the regulation requires flood risk to be considered.
The structural shell is not a generic basement wall upgraded later. Its thickness, load basis, openings and interfaces are part of the shelter definition. This strongly favours early coordination with the main structural concept.
Switzerland
BABS describes the protective shell as the floor, walls and ceiling constructed in reinforced concrete. Openings are closed with blast doors and blast-resistant covers, also designed as protective elements.
The TWP and TWK technical instructions provide the construction and dimensioning basis for protective structures. BABS continues to publish and update these technical-document sets.
Swiss shelter design emphasises the continuity of the protective envelope. The practical project issue is therefore not only concrete strength or thickness, but the entire boundary condition: shell, closures, penetrations, emergency egress and ventilation interfaces.
5. Openings, access and emergency egress
Finland
The Finnish technical rules treat doors, hatches, penetrations, valves and other shelter-specific devices as regulated equipment categories. Penetrations through the protective envelope must match the shelter’s required strength and tightness and be closable from the shelter side.
S1 shelters require an airlock room or airlock tent provision. S2 and rock shelters use more substantial separated technical and airlock arrangements.
Switzerland
Every shelter includes an emergency exit or escape tunnel so that occupants can leave even if the normal entrance is unusable after building collapse.
The shelter envelope is closed by blast doors and blast covers. Larger shelters use airlocks so that entry and exit do not defeat the protective ventilation condition.
Openings are among the most interface-sensitive parts of any shelter. They connect architecture, structure, ventilation, access, installation tolerances and product compliance. They should therefore be frozen only after all disciplines agree on their function and location.
6. Ventilation, filtration and overpressure
Finland
Decree 506/2011 is very explicit.
The shelter must receive pre-filtered air at not less than:
- 2.7 dm³/s per m² of actual protected area in the relevant ventilation mode;
- 0.9 dm³/s per m² during filtration.
The ventilation system must be able to operate independently of the electricity supply.
The shelter must be capable of maintaining at least 50 Pa overpressure.
The intake air must be capable of being filtered for toxic substances. S1 shelters must be designed so that detection/identification equipment can be installed; S2 and rock shelters require the capability to detect and identify toxic substances.
For S2 and rock shelters, fresh-air and exhaust ducts are separate, with the intake and exhaust openings at least 10 m apart.
The ventilation plant is not ordinary comfort HVAC. It is a protective system with different operating logic, filtration, pressure control and independence requirements. Treating it as late-stage MEP fit-out creates predictable coordination risk.
Switzerland
BABS describes the standard ventilation chain as:
- air intake;
- blast/explosion-protection valve;
- pre-filter;
- ventilation unit;
- NBC/gas filter;
- overpressure/explosion-protection valve.
Larger shelters can include airlocks and duplicated protective equipment.
BABS also publishes specific technical specifications for small and large ventilation units, NBC filters and protective valves.
The Swiss model makes the product ecosystem unusually visible. The ventilation system is not only a design concept but a set of approved or specified protective components whose documentation, installation and maintenance become part of compliance.
7. Equipment, product documentation and component lifecycle
Finland
Government Decree 409/2011 requires permanent product markings and addresses product information, operating instructions, maintenance instructions and installation instructions.
The planned service life must be at least:
- 30 years for shelter devices and equipment when storage and maintenance instructions are followed;
- 50 years for devices or parts fixed to concrete structures.
The same regulation includes environmental and shock-resistance requirements for shelter-specific equipment.
For technical procurement, compliance is not just a product model number. Markings, instructions, design life, environmental resistance and installation requirements are part of the deliverable.
Switzerland
BABS maintains technical specifications for protective components and a system of tested/approved components. Its 2025 and 2026 protective-structures work also places increasing emphasis on renewing ageing components while preserving the long-life concrete shell and major closures.
An explanatory federal report states that components and equipment in protective structures reaching around 40 years are to be renewed, with specific exceptions such as major concrete protective closures, while seals still require replacement.
The Swiss system illustrates a lifecycle split between long-lived civil structure and shorter-life technical components. This is a useful model for asset planning because structural continuity does not eliminate the need for planned equipment renewal.
8. Peacetime use and change control
Finland
Public/regulatory logic
Finnish shelters are commonly used during normal conditions for secondary purposes, provided that the shelter can still be prepared for protective use and the technical requirements are not compromised.
The Rescue Act requires the shelter and its equipment to remain in a condition that allows the shelter to be brought into use within the statutory readiness period.
Dual use is not free use. Storage, partitions, services and everyday fit-out should be designed so that conversion to protective use remains practical.
Switzerland
BABS explicitly allows everyday use, for example as storage, basement, workshop, play room, club premises or archive.
However:
- the protective shell may not be altered in a way that compromises protection;
- blast doors/covers and ventilation equipment must remain functional;
- structural or technical modifications require authority approval.
This is a clear change-control principle: normal-time value is allowed, but the protective boundary and systems remain controlled assets.
9. Operational readiness, inspection and maintenance
Finland
Section 76 of the Rescue Act requires the shelter and civil-protection equipment to be maintained so that the shelter can be taken into use within 72 hours.
Decree 506/2011 requires shelter devices to be inspected and maintained at least every 10 years, with device-specific records available to the rescue authority on request.
Switzerland
BABS requires shelters to be capable of being made ready for occupation within five days.
Owners are responsible for maintenance and accessibility. Authorities carry out periodic shelter inspections at least every 10 years.
The readiness values are not construction durations. They are operational conversion targets for existing assets. This distinction matters because a shelter can be structurally complete yet operationally unready if equipment, access or normal-time use has not been managed.
10. Technical comparison matrix
| Dimension | Finland | Switzerland |
|---|---|---|
| Basic model | Statutory classes and explicit technical values | Highly standardised shelter system with federal technical instructions |
| New-build trigger | Floor-area thresholds in Rescue Act | Shelter-place planning and local deficit logic; construction obligation remains active |
| Sizing | % of building floor area or 0.75 m²/person in permitted cases | Standardised occupant-based shelter planning; brochure uses 1 m²/person and 2.5 m³/person |
| Structural pressure basis | S1 100 kPa, S2 200 kPa, rock 300 kPa | Standard mandatory shelter described in TWP as 1-bar shelter |
| Protective shell | Explicit RC minimum thicknesses by class | Reinforced-concrete shell with standardised closures |
| Emergency egress | Shelter-specific access/exit provisions | Emergency exit or escape tunnel is a standard feature |
| Ventilation | Explicit flow rates, filtration and ≥50 Pa overpressure | Standardised intake, blast valve, pre-filter, blower, NBC filter and overpressure/explosion valve |
| Electrical independence | Ventilation must operate independently of electrical supply | Protective equipment designed around civil-protection operation; technical instructions govern components |
| Product documentation | Marking, instructions and equipment requirements in decree | Tested/approved components and federal technical specifications |
| Technical service life | ≥30 years equipment; ≥50 years concrete-fixed devices/parts | Major renewal focus around ageing components; current federal renewal strategy |
| Readiness | 72 hours | 5 days |
| Periodic inspection | Equipment at least every 10 years | Shelter inspection at least every 10 years |
| Peacetime use | Allowed if readiness and function preserved | Explicitly allowed; changes to shell/closures/systems controlled |
11. What this means for project design
11.1 Protection should be treated as an early design input
Both systems support the same project-management lesson: protective requirements work best when they are known before the architecture and MEP layout are frozen.
A shelter affects:
- basement planning;
- structural grid and wall continuity;
- openings and penetrations;
- access and emergency egress;
- plant space;
- ventilation routes;
- water and sanitation provisions;
- normal-time use;
- inspection and maintenance access.
11.2 The protected boundary should be managed as an interface
Every penetration, duct, opening, door and service route can become a cross-disciplinary decision. A strong project process therefore needs an explicit protected-boundary register rather than relying on isolated discipline drawings.
11.3 Product data is part of technical compliance
Where a system relies on specified or regulated devices, the product package should include:
- clear designation;
- applicable approval/compliance status;
- installation requirements;
- interface dimensions;
- operating and maintenance instructions;
- service-life information;
- traceable revision status.
11.4 Readiness is a lifecycle property
A shelter is not finished when concrete is cast or when ventilation is installed. Readiness depends on continued access, maintenance, inspection, documentation and the ability to reverse normal-time use quickly.
12. Source boundary
This baseline intentionally does not provide:
- explosive charge weights;
- standoff calculations;
- pressure and impulse curves;
- reflected-pressure calculations;
- structural member sizing;
- component selection for a live project.
Those belong to qualified specialists using the project’s actual threat basis and current governing requirements.
Primary sources
Finland
- Rescue Act 379/2011, Finlex
Open source ↗ - Government Decree on Civil Defence Shelters 408/2011, Finlex
Open source ↗ - Amendment 1378/2018, shelter location, Finlex
Open source ↗ - Ministry of the Interior Decree 506/2011, technical requirements and maintenance
Open source ↗ - Government Decree 409/2011, shelter devices and equipment
Open source ↗
Switzerland
- FOCP/BABS, Shelters for the population
Open source ↗ - FOCP/BABS, Documents on protective structures
Open source ↗ - FOCP/BABS, Technical documents for protective structures
Open source ↗ - TWP 1984, Technical instructions for mandatory shelters
Open source ↗ - FOCP/BABS, Protective structures: an investment in protection and security
Open source ↗ - FOCP/BABS, Explanatory report on the Civil Protection Ordinance revision
Open source ↗ - FOCP/BABS, Shelter setup and components brochure
Open source ↗