Mass. Gen. Laws ch. 272 § 86A
No person shall stable a horse or mule above the first or ground floor of any building not equipped with an automatic sprinkler system, or horses or mules exceeding six in all on the first or ground floor of any building not so equipped, unless there are two unobstructed means of exit from each floor whereon it or they are stabled, as far apart as practicable and so constructed as to grade that the said animal or animals can quickly and safely leave the building in case of fire and approved as to situation, arrangement and utility by the chief of the fire department. The person in charge of horses and mules stabled in any building not equipped with such a system and requiring two exits as aforesaid shall cause each such animal to use each such exit at least once a week. This and the four following sections shall apply only to cities.
Mass. Gen. Laws ch. 272, § 86A