Code of practice for construction of underground air-raid shelters in natural soil
1969 Edition

The walls must have a minimum thickness of 30 cm and be engineered to withstand an external uniform pressure of 10 tons per square meter. Reinforcement includes dual steel mesh layers placed near each wall face with mesh spacing not exceeding 15 cm for main reinforcement and 20 cm for additional mesh, using steel bars at least 8 mm in diameter. The total steel content should be no less than 0.5% of the wall volume. Roof slabs require a minimum thickness of 20 cm, designed to support self-weight plus dead loads from earth or gravel coverings (250 kg/m² per slab), a superimposed load of 1000 kg/m², and any concentrated loads. Reinforcement bars must be at least 8 mm in diameter, spaced no more than 15 cm apart, with steel volume not less than 0.5% of slab volume. Maximum spans are 4 meters for single-direction reinforcement and 6 meters for two-way reinforcement.

Shelter walls should be constructed using reinforced concrete with a minimum thickness of 30 cm, designed to resist 10 tons per square meter of external pressure. Reinforcement comprises two layers of steel mesh with a maximum aperture of 15 cm for primary reinforcement and 20 cm for secondary mesh, using steel bars with a minimum diameter of 8 mm. The steel content must be at least 0.5% of the wall volume. Roof slabs must be at least 20 cm thick, capable of supporting self-weight, earth or gravel cover loads (250 kg/m² per slab), and a superimposed load of 1000 kg/m². Reinforcement in slabs requires bars no less than 8 mm in diameter, spaced not more than 15 cm apart, with steel volume also at least 0.5% of the slab volume. Concrete used should be monolithic, waterproof, and damp-proof with no conduits for water or gas within walls or slabs.

To minimize blast impact, passages and shelter openings must not be aligned coaxially to prevent direct transmission of blast waves and splinters. Passages and shelter openings require minimum free dimensions of 0.90 m by 0.70 m, while outer openings must be at least 0.70 m by 0.70 m and situated at least 2 meters away from the building's external line. Passage designs must prevent flooding and include blast-resistant features such as two-leaf doors that open inward, lockable from inside, with ventilation provisions. External doors must be reinforced by blast-proof walls. Connecting passages should intersect at right angles creating blast pockets and have oversailing corners to reduce casualties.

Each shelter is designed to accommodate no more than 50 occupants, with an allocation of 0.4 square meters per person, resulting in a maximum shelter area of 20 square meters. Larger shelters should be subdivided into sections housing up to 50 individuals each using traverses, zigzag walls, or doglegs to reduce risk and facilitate safer evacuation.

Yes, shelters situated outside building limits must comply with all provisions of the standard except Clauses 6 and 7. For shelters within building limits, walls should be positioned at least 2.0 meters away from the building's external walls, with a preference for basement locations when available. Exceptions can be authorized by competent authorities in special circumstances. Shelters must be dispersed to avoid concentration, limiting occupancy to 50 persons per section separated by partitions such as traverses, zigzags, or doglegs. The final location and layout decisions rest with the competent authority to ensure safety and practicality within urban constraints.