Maryland Code, Health-General § 24-505

(1) Private homes, residences, including residences used as a business or place of employment, unless being used by a person who is licensed or registered under Title 5, Subtitle 5 of the Family Law Article to provide child care, and private vehicles, unless being used for the public transportation of children, or as part of health care or child care transportation;

(2) A hotel or motel room rented to one or more guests as long as the total percent of hotel or motel rooms being so used does not exceed 25%;

(3) A retail tobacco business that is a sole proprietorship, limited liability company, corporation, partnership, or other enterprise, in which:

(4) Any facility of a manufacturer, importer, wholesaler, or distributor of tobacco products or of any tobacco leaf dealer or processor in which employees of the manufacturer, importer, wholesaler, distributor, or processor work or congregate; or

(5) A research or educational laboratory for the purpose of conducting scientific research into the health effects of environmental smoke.