SFPE Handbook of Fire Protection Engineering. 3rd Edition, DiNenno, P. J.; Drysdale, D.; Beyler, C. L.; Walton, W. D., Editor(s), 5/93-104 p., 2002. Chapter 7; Section 5; NFPA HFPE-02. See http://fire.nist.gov/bfrlpubs//build02/art155.html.
William G. Sullivan, Elin M. Wicks, and C. Patrick Koelling, Engineering Economy, Fourteenth Edition, Upper Saddle River, New Jersey: Pearson/Prentice Hall, 2009, page 120.
Chinyere Onwubiko, An Introduction to Engineering, Mission, Kansas: Schroff Development Corporation, 1997, page 205-206.