Thailand – Australia – United Kingdom

Tech Diving Expedition: Trimix Diving Sunken Forest

Technical divers explore sunken forest on helium filled mixed gas

Khao Sok National Park, Thailand

Continuing the expedition James Foleher and James Thornton-Allan started the second day in Khao Sok National Park to commence open lake trimix diving and cavern diving over the next few days in a man made called Chiew Larn Lake which is part of Rachaprabha Dam located inside the national park.

Preparing for the days diving included mixed helium, oxygen and nitrogen into our twin cylinder diving tanks to make trimix. Trimix is used to remove the effects of the element nitrogen which causes nitrogen narcosis, additionally it’s used to remove oxygen content to dive blow the normal limit of oxygen in air. Our mix today would be 19/38 (19 percent oxygen and 38 percent helium) which leaves the rest as nitrogen. This means a dive to approx 60 meters would feel like a dive to 25 meters. This gives the divers a clear head for dive.

A clear head was certainly needed for the first dive which would be a dive to explore the sunken forest which was submerged when Rachaprabha Dam was constructed. The sunken forest is a maze of vines, trees and rocks in night conditions as the light is blocked by the heavy sediment in the water. Despite the darkness the clarity of the water is quite high and visibility is only limited by the strength of the underwater torches worn by the divers.

Diving in the forest requires many diving skills including a calm attitude and ability to task load since using a reel is important so you can get back to a clearing, breaking through the canopy of the trees on ascent can be difficult.

During the ascent portion of the dive a new cave was found, a very large cave that was able to house both divers during one of the stops. There was no room for exploration as it was during a strict decompression schedule but the location would be marked for future trips.

One striking difference was the change in water that shifted from 32 degrees Celsius to 22 degrees at the bottom making it quite difficult to dive in only a thin tropical wetsuit.

Upon reaching the surface the divers loaded back in the wooden boat and moved to “Temple Cave” to begin the official TDI Cavern Course. However since the water level has dropped due to lack of rain and constant decanting through the power plant this cave was very much out of the water. Many of the most attractive features were above water. This water level combined with the fact the first 10m of the water is bright green meant the dive conditions would be quite poor.

As a team it was decided to not waste time exploring the almost dry cave and head for the next destination of Khao Lak and change the schedule to return at the end of the expedition when the water level might rise. Alternatively many of the future destinations will offer the cavern environment and could be continued there.


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