Mines are man made and inherently a higher risk environment than the vast majority of natural caves. A cave is formed over a long period of time and its intrinsic stability is due to this. Mines are cavities excavated over a relatively short time period and not there because of any natural process. Mine diving is not within the specific training remit of the CDG although it is accepted that CDG members will dive in mines. From a CDG perspective they can offer an all-weather training environment with (normally) dependable visibility.
The following considerations need to be addressed:
- Passage stability
- Man made artefacts making entanglement hazards and traps.
- Water toxicity
- Air toxicity
- Stacked “deads” (waste rock)
- False floors
- The temperature of the water in a mine can be colder than in a cave (UK).
Any dive in a mine should follow much the same process as diving in a cave.
- Any access requirements or permits needed.
- History of the mine (gives an idea of what to expect).
- Any surveys from its active period.
- Recent diver derived surveys.
- Look for information on previous dives (CDG NL).
- Stability of the entrance passage.
- Access to the water.
- Equipment needed to access the water.
- Decompression considerations.
The equipment required is as you would use for a cave dive with some cautions.
- Standard search reel methods can be used with the caution.
- Direction often cannot be predicted by passage features i.e. scallops, ripples in the mud, although vertical navigation is still aided by bubble movement.
- Some metal mines will result in unreliable compass readings.
- Staying still for too long can cause a higher risk of roof collapse than in a cave, as bubbles will make the roof less stable due to a more fractured roof. (Rebreather divers may be safer than those using open circuit equipment). Good buoyancy control and finning technique will help (a bit).
- Although visibility may be good initially, it can reduce to zero very quickly. This is due both to movement and bubbles.
- Consider taking a gas analyser as the air beyond a flooded passage may be of poor quality. This must be protected from water on the dive. Low levels of O2 can render a diver unconscious in seconds and dead within minutes.
- Keep breathing from the valve while the air quality is checked.
- Dive lines may be very thin (i.e. more suited to clear overseas sumps). It can be hard to manage whilst wearing thick gloves and in poor visibility. It is far easier to become entangled in.
- If the mine is a training site lines may criss cross (laid as a training exercise).
- Junctions may be frequent so take clearly identifiable junction markers.
- If in doubt remove suspect line and lay your own.
- Wash the gear bearing in mind that a lot of mines can have higher alkaline or acidic levels than (most) natural cave waters.
With Thanks to John Cordingley for proofreading and comments.
A M Ward 2016 CDG