The requirements for the M-1 light industrial and research and development district are intended to apply to an area located in close proximity to transportation facilities and which can serve light manufacturing, research and development, distribution and other industrial functions. Restrictions in this division are intended to minimize adverse influences of the industrial activities. All principal uses permitted in this zone shall be contained in an enclosed structure. All buildings in this district shall be considered in the fire district, as per the definition in section 110-1, and built in conformance with the rules and regulations of fire districts.