Universities and other large institutions, such as hospitals, often distribute steam for heating buildings and autoclaves from a central heating plant. These high pressure steam pipes are generally run through utility tunnels, which are often accessible solely for the purposes of maintenance. Many of these steam tunnels, such as those on college campuses, often also have a tradition of exploration by its students. This was once called vadding at MIT, though students there now refer to it as roof and tunnel hacking.
Steam tunnels, in general, have been secured heavily in recent years, due to their use for carrying network backbones and perceived risk of their use in terrorist activities, safety and liability.
Some steam tunnels have dirt floors, no efficient lighting and have temperatures upwards of 45 °C (113 °F). Others have concrete floors, bright light, and feature a cool low-grade temperature. Most steam tunnels have large intake fans to bring in fresh air and push the hot air out the back. Most active steam tunnels do not contain airborne asbestos but proper breathing protection may be required for other hazards. It is wise to take proper care inside active utility tunnels, since pipes can spew boiling hot water from leaky valves, puddles pool at your feet, and forceful steam may leak inward resulting in burns and slips.