Safety should be a primary concern of every urban explorer. It's easy to underestimate the very real dangers of going underground (or overground) in the city and on campus. Dont make that mistake! Here are safety tips for tunnels, drains, and abandoned buildings. If you have any suggestions. And remember, NJE does not endorse its readers doing anything illegal. Application of this information in a real world setting is an at-your-own-risk proposition.
Some general guidelines. First, always let someone trustworthy know where you're going. Second, avoid exploring by yourself unless an uncommon and irresistible opportunity presents itself unexpectedly. Third, check the equipment list and be sure to have the top four "American Express" (don't leave home without it) items: light, batteries, gloves, and a knife. Fourth, be aware of your surroundings. Know how and when conditions may change to affect you (for example, a routine janitorial shift change which will put people in your area), and notice the physical (like a ladder which may be unbolted from the wall halfway down). Now, onto specifics.
Asbestos. Unless there's positive reliable information as to absence of asbestos in the system, wear a respirator. Most institutional tunnels still have asbestos hanging around. Nobody can really say for sure at this point what asbestos will or won't do to you based on certain amounts of exposure (though its effect is definitely cumulative rather than immediate), but it is linked to an agonizing and untreatable lung cancer as well as other diseases. So, consider the risk and know that the effects of exposure are dramatically increased on those who smoke. Check the "equipment" section for specific info on respirators.
Machinery/miscellaneous equipment. Basically, don't touch any of this stuff. Turning valves, flipping switches, etc. can easily do more than just annoy someone who suddenly finds themselves without heating or some such. It can be hazardous for the explorer and for people topside; this is especially true for valves on steam lines. Never touch these. It may cause dangerous pressure changes in the line.
Personal security. This means, safety from the authorities. Keep an eye out for motion detectors, door-wired alarms, etc. It's a good idea to examine doors before opening for magnetic and wire detection devices. If you're an amateur please don't try to James Bond your way around security devices, you'll just draw attention to your fellow explorer's activities. Also, of course, be aware of security cameras. I don't know of any tunnels that have them, but many commons areas do, and the last thing the intrepid adventurer needs is to come out of a manhole on the Mall or a wall hatch in the Student Union and be smiling for Kampus Kops' Kandid Kamera.
Watch where you step...or lean, or crawl. When you're getting around and over and under and between the myriad pipelines which run through the tunnels, it's often tempting to use them as handholds, braces, even steps. You should avoid this in most cases. Always keep in mind...a steam line rupture anywhere in your vicinity of a standard ~250psi system is going to result in an inevitable lobster-style death for everyone around, and even relatively minor damage will likely result in tighter security (read: less fun), so think twice before sitting on that pipe.
Contaminants. See the Tunnels column for asbestos information. Aside from that, abandoned buildings can be home to basically anything you can think of. Industrial waste, used solvents, airborne mold spores (can cause asthma), biohazard material, used needles from squatters, old festering grease, and all sorts of other gnarlies. Consider at least a dust mask and watch where you're putting your hands and feet.
Machinery. You'd be surprised what still may have juice running through it. Don't do anything stupid, and wear gloves of you're gonna mess with old rusty junk - infected metal splinters are not fun.
Structure. If it's been abandoned for long there's always a chance of things falling down around you. It's not uncommon to lean against a support and feel it start moving -- not good. Watch for floors and ceilings which seem to be buckling, and proceed cautiously on staircases. There's word of a group who went running up one and the first guy in line took a nice fall to the previous landing when a stretch of about 5 steps just wasn't there. On the other hand, if the place is obviously being left to rot don't be afraid of prying open a crusty old door or two with your trusty crowbar. That's what exploring is all about!
The classic rule...When it rains, no drains.This is a long-standing creed for a good reason. When you have a complex system draining large areas, it's amazing how quickly flow increases. Remember, walking in even ankle deep water can be extremely difficult if the current is swift enough, and water levels can rise very quickly in drains leaving you gasping for that last inch of air at the top as you wash towards certain death at a 30 foot waterfall around the next bend. Get the picture? In a similar vein, always explore heading against the flow of the water...if you get carried away you won't be launched into unknown deathtraps.
Shafts. Check step irons closely. They'll often crumble in your hands or pull out of the wall. Test them before trusting your weight to them, especially in taller shafts. If the shaft is small enough diameter to comfortably chimney it, consider doing so if the irons look old or corroded, or feel unstable. "Chimney" is the word for bracing your back against the wall and using your feet against the opposite side and your hands against the back wall to move yourself up or down.
Funk. Be careful where you're stepping and what you're touching...if you get into areas of sanitary sewage ("sanitary" being the official word for stuff that isn't), it's common to end up with nasty bacterial illnesses soon thereafter. Also, any open wounds (including common things like dry skin which has cracked) can provide entry points for infection. In storm drains this isn't often a problem, but sanitary overflow may be present in normally "clean" drains at times.
Bad air. This is a concern in any enclosed space, especially drains. If people in the group start feeling sick, light-headed, dizzy, etc., get back out into fresh air ASAP. Don't count on smelling bad air; many deadly gaseous compounds have no odor. In addition to bad air, combustible gasses can be present. Think very carefully about open flame or sparks unless you're sure the drain is safe. And never drop a burning rag etc. down a shaft to test the air. This can cause not only structural damage but also personal injury if it happens to set off a fireball. Explosions which take out entire city blocks have been known to orginate in drains so think twice. Additionally, keep in mind the ever-present possibility of industrial and biohazard waste being dumped in drains. If you start seeing hypodermics, bizarre sludge, etc. be careful.