Nothing in this chapter shall be deemed to prevent
normal maintenance and repair or structural alteration in nonconforming
buildings, provided that such action does not increase the degree
of or create any new nonconformance with regard to the regulations
pertaining to such buildings. Further, nothing in this section shall
be deemed to prevent the carrying out, upon issuance of a building
permit, of major structural alterations or demolition in the interest
of public safety.