They were required well before 1991. According to the article below, it was mandated by law as early as 1976:
http://www.nytimes.com/1987/08/25/nyregion/new-york-gets-tough-on-window-guard-law.html
They were required well before 1991. According to the article below, it was mandated by law as early as 1976:
http://www.nytimes.com/1987/08/25/nyregion/new-york-gets-tough-on-window-guard-law.html