The requirements for fire extinguishers are detailed in sections 15-16-620 through 15-16-700. The code refers to NFPA 10 for specific governance. NFPA 10 is a set of standards related to fire extinguishers, published by the National Fire Protection Association, and is generally used as the "rule book" for fire extinguishers in the United States.
The Chicago Municipal Code is available online here: http://www.amlegal.com/codes/client/chicago_il/.