Mine Features and Hazards

Common features in a mine include drifts (horizontal tunnels), shafts (vertical tunnels) and winzes or air vents that are much smaller and can be at any angle underground. Climbing through these shafts, tunnels, and winzes can be very dangerous due to their unseen entrances and exits. A drift with a portal to the outside is called an adit.

Stopes (areas where ore was removed) usually follow the ore vein and are often at steep angles to horizontal. Many stopes are shored with wooden 2x4s or 4x4s. Contrary to what one might think, the wood isn't there to keep the stope from collapsing, but rather to hold loose rock in place. Some stopes are narrow and convoluted, others resemble giant rooms.  Many stopes have a lot of loose material on or around them; extreme caution must be exercised.

Raises are often used to transit vertically between levels of a mine. A raise is often a 6-12 foot square vertical shaft divided into two sections. One half is a straight drop to the bottom and is used for haulage, and the other section is a series of platforms, 10 or more feet apart, with holes cut in them in an alternating manner. Beneath each hole is a ladder leading to the next platform. This style of construction affords safety: if one falls off the ladder, the fall is only to the next platform, not the bottom of the shaft.

Mines were generally constructed and maintained to be safe while they were operational. After they are abandoned, workings may decay to a point where they could become dangerous. For instance, some support structures may have been removed before abandonment for re-use elsewhere, or supporting pillars may have been quarried away, leaving the chamber unstable. Ventilation and water pumping systems that once maintained safe working conditions are removed.

There are a number of potential hazards that mine explorers face:

• Surface shafts: The ground around abandoned mine shafts and open pits may be weak and could cave-in without warning. Undergrowth may hide shafts, while timber used for capping may have rotted to a point where it will collapse if weight is put on it. Even scarier is the so-called "ant-lion trap" effect: loose earth around a surface shaft crumbles away over time, leaving a funnel-shaped drop-off around the shaft. If a curious person attempts to look down the shaft, he or she could begin sliding into it with nothing to stop the fall.

• Collapses: The effects of blasting, weathering, and earthquakes destabilize once-strong bedrock through time. Portals (adits) in particular are affected, but tunnel and chamber roofs and walls can also destabilize. Support timber props, ladders and other similar structures may appear safe but could have degraded. Similarly, waste rock tipped down chambers may be unstable and rockslides may occur if they are walked on. If it doesn't look right, it's better to leave it unexplored than to risk one's life unnecessarily.

• Darkness: As with most underground places, the darkness in a mine is total. If you lose light, it may be difficult or impossible to exit the mine. An experienced explorer will carry at least three independent sources of illumination and a set of spare batteries.

• Falling: Falling down vertical openings is the most common cause of death and injury in abandoned mines. Winzes are vertical or inclined shafts sunk from a tunnel and these can be hidden by darkness, water, loose debris or false floors. False floors may also be present in substantial lengths of tunnel, where the floor level has been worked (understoped). Such floors may be supported by rotten wood, but surfaced with rock and not clearly distinguishable from a solid floor. A prudent explorer wears a hard hat or climber's helmet: even if one doesn't fall, many passages are irregular and low, and a protruding rock can carve a nice gash in one's head while walking through.

• Water: Water in mines is often deep and can be dangerously cold; if it fills an area with steep sides, then it may not be easy to climb out. Seemingly shallow water can conceal sharp objects, drop-offs, and other hazards. Furthermore, a wet mine can rot or rust timbers, shoring and ladders, making conditions hazardous. Desert mines tend to be dry and therefore relatively safe in this regard; however, dry rot can weaken wood. All ladders and wooden floors should be tested before trusting body weight to them.

• Bad Air: Old mine workings may be hazardous due to pockets of blackdamp (still air with low oxygen levels), or high concentrations of methane, carbon monoxide, carbon dioxide or hydrogen sulfide which can displace oxygen, poison someone outright, or create an explosion. Coal mines are especially prone to containing these gases. If a mine is not well-ventilated or conditions are unknown, use of a properly-calibrated 4-gas detector (O2, CO2, CO, and H2S) is recommended.

• Explosives: Explosives such as dynamite, black powder or blasting caps may have been abandoned in old mines. Many explosives become increasingly unstable with age and could be detonated by the slightest movement or even the vibrations from a footfall.

• Wildlife: Snakes, various mammals, and bats can call a mine home. Exercise caution, especially near mine portals.

• Hazardous chemicals: Mines dug in wet areas give underground water a path to percolate through rock and exit via the tunnel systems. In some areas, the mine water can contain various types of heavy metals. Bacterial action can create acids and other compounds that are hazardous to humans. Acid mine drainage is of great concern in some areas. Also, mills and other processing areas may contain traces of cyanide and mercury compounds that were once used to separate precious metals from the ore.

• Remoteness: Most mines are a long way from medical assistance, and depending on the circumstances, just getting to the surface could be an ordeal if one is injured. The cardinal rule of mine exploring is to never do it alone. Also, someone not with the party should be informed of where the group is going and when it plans to return.