Editing Urban exploration (section)

===Utility tunnels===
{{main|Utility tunnel}}
[[File:Schiffbau tunnel.jpg|thumb|[[Utility tunnel]] in the center of [[Zürich]], Switzerland]]

Universities, and other large institutions, such as hospitals, often distribute hazardous [[superheated steam]] for heating or cooling buildings from a [[district heating|central heating plant]]. These pipes are generally run through utility tunnels, which are often intended to be accessible solely for the purposes of maintenance. Nevertheless, many of these steam tunnels, especially those on college campuses, have a tradition of exploration by students. This practice was once called "vadding" at the [[Massachusetts Institute of Technology]], but students there now call it [[roof and tunnel hacking]].

Some steam tunnels have dirt floors, poor lighting and temperatures above {{convert|45|C|F}}. Others have concrete floors, bright light, and more moderate temperatures. Most steam tunnels have large intake fans to bring in the fresh air and push the hot air out the back, and these may start without warning. Most active steam tunnels do not contain airborne [[asbestos]], but proper breathing protection may be required for other respiratory hazards. Experienced explorers are very cautious inside active utility tunnels since pipes can spew boiling hot water or steam from leaky valves or pressure relief blow-offs. Often there are puddles of muddy water on the floor, making slips and falls a special concern near hot pipes.

Steam tunnels have generally been secured more heavily in recent years due to their frequent use for carrying communications network backbone cables, increased safety and liability concerns, and perceived risk of use in terrorist activities.