As used in this article, the following terms shall have the meanings indicated:
FALLOUT SHELTER; SHELTER
Any building or structure or part thereof designed and used in accordance with this article for protection against atomic radiation resulting from nuclear explosions.
FAMILY SHELTER
Any fallout shelter built as an accessory to a single-family or two-family dwelling and designed for the protection of the occupants of such dwelling.
GROUP SHELTER
Every fallout shelter other than a family shelter.
NET AVAILABLE AREA
The floor area of a fallout shelter within the walls of the fallout shelter and available for fallout shelter purposes, such as for sleeping, eating, food preparation, toilets, storage of food, water, bunks and other supplies and material.