The specifications of an above-ground modular shelter contain a few numbers everyone sees and few understand: 500 kPa, 300 mm, 100 kPa, 8 hours, up to 50 people. We break each one down in plain words and compare it with the minimum required by Ukrainian standard DSTU 9329:2025 for primary mobile shelters (PMU).

First, the words: PMU, modular, mobile, above-ground, reinforced concrete

These are not five different shelters but five attributes of one. PMU — primary mobile shelter, the standard's term. Modular — assembled from factory-made modules. Mobile — can be transported and reinstalled. Above-ground — stands on the surface. Reinforced concrete — what it is made of. The "Fortetsia" shelter by Hobbit House meets all five. Now the numbers.

100 kPa — the standard's minimum

DSTU 9329:2025 requires a primary mobile shelter to withstand a blast overpressure of at least 100 kPa. This is the state minimum: a structure that does not withstand it cannot be called a PMU. This is the figure to start from when comparing shelters.

500 kPa — the "Fortetsia" margin

The above-ground "Fortetsia" shelters are designed for 500 kPa — five times the standard's minimum. Why the margin? A real blast wave is never "nominal": distance to the explosion, calibre and ricochets are unpredictable. The safety margin is the difference between "withstood by calculation" and "withstood in reality".

This is not theory: in a proving-ground test, "Fortetsia" withstood the detonation of a 120 mm mine and direct hits from the 125 mm cannon of a T-72 tank.

300 mm — wall thickness per DBN standards

Protection from the blast wave and fragments comes from the mass of the structure. The "Fortetsia" walls are 300 mm of reinforced concrete per current DBN standards. The logic is simple: to stop a fragment and absorb a wave, the material must be heavy and solid. Reinforced concrete combines the mass of concrete with the tensile strength of steel rebar — which is why it has been the basic material of protective structures for decades.

Arch and buttresses — why not a "box"

The "Fortetsia" roof is arched and the walls are supported by buttresses. This is not aesthetics but physics: an arch transfers load to the supports in compression, and concrete performs best precisely in compression. A flat slab under the same pressure works in bending and needs far more material. Buttresses take the lateral pressure and stop the wall from "folding". This gives the structure a safety margin without excess weight.

2 exits, 2 metres, up to 50 people — the standard's requirements for every PMU

The standard requires at least two separate exits (so that one being blocked does not trap people), a room height of at least 2 metres, and sets the capacity of one primary mobile shelter at up to 50 people. The number of places needed on a site is achieved by the number of modules and shelters: the modular design allows the configuration to be matched to the team and the space to be zoned.

8 hours — installation, not construction

Three different times are most often confused: manufacturing, delivery and installation. From 8 hours is the on-site assembly of the structure for basic models; large multi-module shelters are assembled from 1 day. Modules arrive ready from the factory and are placed on a prepared base without construction work — so on site we talk about hours, not a construction cycle. Manufacturing and delivery are planned separately.

All the numbers side by side

• Blast overpressure: DSTU minimum — from 100 kPa; "Fortetsia" — 500 kPa.
• Exits: DSTU minimum — at least two; "Fortetsia" — compliant, confirmed by the DSTU 9329:2025 certificate.
• Room height: DSTU minimum — from 2 m; "Fortetsia" — compliant, confirmed by the certificate.
• Capacity of one shelter: per DSTU — up to 50 people; for "Fortetsia" it is set by the number of modules.
• Installation: per DSTU — on a prepared base without construction work; "Fortetsia" assembly — from 8 hours.
• "Fortetsia" walls: reinforced concrete, 300 mm per DBN standards.
• Confirmation: DSTU 9329:2025 certificate and a full-scale proving-ground test.

FAQ

What does 500 kPa mean for a shelter?
It is the blast overpressure the structure withstands. For "Fortetsia" it is five times the DSTU 9329:2025 minimum (100 kPa).

Why does an above-ground shelter have an arched roof?
An arch transfers load in compression, which is where concrete performs best. The structure withstands more pressure at less weight than a flat slab.

Does a modular shelter need a foundation?
The standard provides for installation on a pre-prepared base without construction work. Base requirements for a specific model are specified by an engineer.

How many people does a modular shelter hold?
It depends on the configuration: one primary mobile shelter is rated by the standard for up to 50 people, and the required site capacity is achieved by the number of modules and shelters. An engineer makes the exact calculation for your site.

Want to understand which configuration your site needs? Share the number of people and the type of site — a Hobbit House engineer will explain the numbers for your case and propose a solution. See above-ground modular shelters, the catalogue of reinforced-concrete shelters and the article "What are primary mobile shelters".