The private shelter market has no equivalent of a building code. The gap between a genuine protective facility and a well-marketed underground room can be several hundred thousand dollars and the difference between protection and false confidence. This guide gives you eight questions to ask before committing.
What is the stated Protection Factor, and where does that number come from?
Protection Factor (PF) is the ratio of external radiation dose to internal dose. PF 1,000 means you receive 0.1% of the external dose. Swiss Level 1 standard specifies PF 1,000 for full protection. The basis for the claim matters — a PF cited from a structural calculation is different from an estimate or a marketing description.
What is the quoted Protection Factor, and is it based on a structural calculation, a measurement, or an estimate? Can you provide the calculation?
What is the blast overpressure rating and what standard was it tested to?
Blast resistance is measured in kilonewtons per square metre (kN/m²). A Swiss Level 1 shelter shell is specified to withstand the overpressure from a defined detonation at a defined distance. There is a published test standard for blast doors (EN 13123). Ask for the certificate.
What is the blast door's kN/m² rating? Is there a third-party test certificate? What standard was it tested to?
What does the NBC filtration system actually include?
Genuine NBC protection requires six components in the filtration train: blast valve, pre-filter, HEPA H13/H14, activated carbon filter, centrifugal fan, and overpressure valve. Some products describe "NBC filtration" when they have installed only a HEPA filter and a fan. Ask for the component list with model numbers.
Can you provide a component list for the NBC filtration train with manufacturer, model, and rating for each component?
Has the shelter shell been pressure-tested to confirm NBC positive pressure capability?
Installing NBC-rated filter components does not confirm NBC protection. For genuine NBC protection, the filter system must maintain slight positive pressure across the entire shelter shell — which requires the shell to be sufficiently airtight. The only way to confirm this is a pressure decay test at 50 Pa. Without a test result, NBC performance is unverified.
Can you show me a shell pressure test result — leakage rate at 50 Pa with the NBC fan running? Is this test done by your installation team or by an independent commissioning engineer?
How is the airlock configured, and what is the decontamination procedure?
An airlock is the sealed entry vestibule between the outside world and the main shelter space. It allows occupants to enter, close the outer door, carry out a basic decontamination, and then open the inner blast door — without introducing contaminated air directly into the protected space. A shelter without an airlock requires opening the main blast door to the potentially contaminated atmosphere to allow entry.
Is there an airlock? What are its dimensions? Is there a shower or wash facility in the airlock for decontamination?
How long can the shelter operate without external power or resupply?
Power is the critical dependency. NBC filtration, lighting, water pump, and communications all require power. A shelter designed to support 4 people for 14 days requires a generator with sufficient fuel, stored on-site, sized to the shelter's calculated load. Ask for the load calculation and the fuel volume specified.
What is the generator capacity and fuel reserve? Can you show the load calculation and the number of hours full autonomy provides?
What is the water capacity, and how is sanitation handled?
Swiss TWK 2017 requires a minimum of 3 litres per person per day for drinking alone. For a 4-person, 14-day shelter, this is 168 litres absolute minimum — but total sanitation water requirements raise this substantially. Sanitation in a sealed shelter must use a contained waste system. A standard drain connection is not adequate in a sealed facility.
What is the potable water tank volume? How is waste water and sewage managed — is there a contained system, and what is its capacity?
What commissioning documentation comes with handover?
A properly commissioned shelter comes with a documented record: blast door test report, NBC filter commissioning record with measured airflow and pressure, generator test record, and a shelter operating procedure. If none of this exists, the facility has not been formally commissioned. That is not a minor administrative gap — it means the stated performance has not been verified.
What commissioning documents are included at handover? Is commissioning done by your team or an independent engineer?
Red Flags in Supplier Responses
| Response Pattern | What It Indicates |
|---|---|
| "Military-grade protection" | Not a technical specification. Has no defined meaning in civil protection standards. |
| NBC claim without a pressure test result | Filter components have been installed but NBC performance has not been verified. |
| Protection Factor given as a range with no source | Estimated, not calculated or measured. |
| Commissioning by the installation team only | Self-certified performance. No independent verification. |
| Water volume not specified | Life support has not been sized to actual occupancy and duration. |
| No airlock in design | NBC protection during entry events is not addressed in the specification. |
We carry out independent shelter assessments and can evaluate a supplier's proposed specification against civil protection standards. If you are comparing options, get in touch.
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