It is unlawful for any person to obstruct, impede or interfere with any officer, agent or employee of the city or with any person who owns or holds any estate or interest in any building or structure, or any portion thereof, which has been ordered to be repaired, vacated and repaired, or demolished, or with any person to whom such building or structure has been lawfully sold pursuant to the provisions of this chapter, whenever any such officer, agent, employee, purchaser or person having any interest or estate in such building or structure is engaged in repairing, vacating and repairing, or demolishing any such building or structure pursuant to the provisions of this chapter, or in performing any necessary act preliminary to or incidental to such work or authorized or directed pursuant thereto.
(`78 Code, § 15.56.220.)