Excerpts from Haixusa.com:

MABAS is an organization that jumps into action in the event of a major incident where the local fire department would be unable to cope on its own. The Mutual Aid Box Alarm System coordinates the response to large fires, train accidents, hazardous material incidents, airplane crashes, earthquakes, and other emergencies with large numbers of causalities, providing intelligent and effective standardized rescue methods. It can mobilize 38,000 of the 40,000 firefighters in Illinois, and assists fire departments in Iowa, Indiana, and Wisconsin, while also providing equipment. The system is funded by its member organizations and no one is charged for its services. 

HAIX® traveled through the suburbs of Chicago and up north to Wheeling, the home of MABAS Division 1. As we traveled the facility, there were trucks of all sizes loaded with tons of equipment and trailers with back-up material, including 500 ladder trucks, 1,300 ambulances (many paramedic capable), 250 heavy rescue squads, and 1,000 water tenders. Fire/EMS reserve units account for more than 1,000 additional emergency vehicles. These are the vehicles that a single fire station could never afford. There are also double-decker boat trailers, mobile ventilation units, and mobile post commands.

In 1970, the MABAS system was established to provide a swift, standardized, and effective method of mutual aid assistance for extra alarm fires and mass casualty incidents. Today, the organization includes nearly every fire department in Illinois, as well as many areas of Iowa, Indiana, and Wisconsin. MABAS-IL includes approximately 1,000 of the states’ 1,200 fire departments organized within 67 divisions. MABAS-IL divisions span an area from Lake Michigan to the Iowa border and south almost into Kentucky. Twelve Wisconsin divisions also share MABAS with their Illinois counterparts. The cities of Chicago, St. Louis, and Milwaukee are also member agencies.