His work with the New York City Municipal Board of Health led to a number of important sanitary reforms in the city. When he began his services on the Board of Health in 1866, 53 out of every 100 deaths in the city were children under the age of 5. He implemented major reforms to improve infant nutrition, including stopping the sale of watered-down milk, and instituted a corps of traveling Physicians to tend to the residents of tenements. By the time he left the Board, the child mortality rate had fallen to 46 out of every 100 deaths, an estimated saving of 8000 lives and 5000 children per annum. He was a strong advocate for tenement reform, designing tenement houses that were cleaner and brighter than those most prevalent in the City, and pushing a "Tenement House Act" through legislature. This is all in addition to the more mundane tasks of testing household goods such as cosmetics, patent Medicine, and wallpaper for toxic and potentially harmful additives. The Board of Health, under his leadership is credited with preventing a cholera epidemic in 1883. He, himself, thought his most important work with the Board of Health was his work in reducing fatal Kerosene related accidents through informing the public about the dangers of Kerosene with naphtha and gasoline added (making combustible vapors). All in all, Chandler's leadership of the Board of Health marks an important chapter in the history of sanitation in New York.