Both parties have approached and argued this case as if it had grown out of the procedural matrix of G. L. c. 143, Section 8 (as most recently amended by St. 1972, c. 802, Section 24), which, in a city, requires the convocation of a board consisting of the city engineer, the head of the fire department and a disinterested person if the owner of an unsafe structure refuses to comply with the requirements set forth in a notice from the building inspector to make such structure safe or to remove it. Section 8 requires the board to conduct a "careful survey of the premises" and to submit a written report, a copy of which is to be served on the owner. In reality, this is an action to abate a nuisance brought under the first clause of G. L. c. 143, Section 12 (as most recently amended by St. 1972, c. 802, Section 27), which is entirely independent of G. L. c. 143, Section 8. See Medford v. DiFilippo, 347 Mass. 327 , 330 (1964). The judge, like the parties, proceeded on the erroneous assumption that Section 8 was applicable in the circumstances. It was not, and all evidence of the contents of the letters should have been excluded.