National Diving Centre

by Clive Bowen

8:30 am on a bright Tuesday morning. Dave Simmons and I are on our way down to the new National Diving Centre in Chepstow to do my last 2 qualifying dives for the IANTD NORMOXIC Trimix course. After an uneventful 2 hours journey, we cross the old Severn bridge and the sky is bluer, the sun is warmer and the grass is greener – well, we are in Wales!

We meet my dive buddy Lesley in the car park – with my car there, that makes 3 in total! We’re in no rush; we’re only doing 1 dive a day, so it’s an opportunity to have a look around the site. The site was an old stone quarry and was opened earlier this year as a diving center. It has a well-stocked shop, toilets, café and a state-of-the-art gas filling station, which fills air Nitrox and Trimix. It also has a recompression chamber. Later on this year it will open an indoor pool as well. The staff are friendly, helpful and very experienced. To dive here costs £12.50, and if you become a member for £15, this drops to £9.50. The site is open 7 days a week – 9:30 am to 5 pm during weekdays and 8 am to 5 pm at weekends

Because the car park is high above the lake, during busy periods you load you and your kit into a trailer, which then takes you down to the pontoons. If it’s quiet you can drive yourself to the pontoons and leave your car at the lower car park, which is what we did. The pontoons run down the lake for approx 100 m giving divers plenty of space to enter and exit the water and to choose where. There are kitting up tables too. We were kitting up and entering the water at the far end, so be prepared for a bit of a walk!! The first part of the quarry is around 20 m deep and has a few attractions such as a divers wet bell. It then drops down a sheer wall to approx 46 m and then gradually slopes down to approx 80 m. There are 3 buoys in this area, a 50 m, a 75 m and a free diving one. Both the 50 m and 75m buoys have a trapeze on them, to help with long decompression stop.

Our plan on this first dive is for me and Lesley as a buddy pair to drop down the 50 m buoy and get down to approx 54 m and do a 20 min bottom time with a total time of 58 min. We’re using Trimix 22/24 as a back gas with Nitrox 75 as a deco gas. For the less tech-minded: Trimix is a mixture of 3 gases, oxygen, nitrogen and helium. By reducing the nitrogen content in the mix, and replacing it with helium it reduces our susceptibility to narcosis at depth. Trimix 22/24 means a mix of 22% oxygen, 24% helium and the remainder 54% being the nitrogen. This gives us what’s called an equivalent narcotic depth (end) of 30 m. So at 54 m as narked as diving on air at 30 m. Deco gas is Nitrox 75, which is 75% oxygen which aids in quicker decompression times and cleanses the nitrogen out of the system quicker, thereby reducing the changes on DCI.

Whilst we’ve been discussing the plan and then kitting up, both Dave and myself have become aware of Lesley’s nervousness. She tells us that she doesn’t like low-viz diving, though we have been told that the viz here is OK with reduced viz in the top 20 m or so, due to algae bloom. After a long time kitting up and repeated checks on Lesley, we’re ready to get in. It’s nice to get in the water to cool off and help take some of the weight off your back. A short swim out to the buoy, a final check and we start our way down. We stop at 6 m to do a bubble check to ensure that there are no leaks anywhere. Then Dave leads the way with me, alongside Lesley. We’re both keeping an eye on her during the very slow descent. When at around 26 m she signals ‘up’ to me and makes a bolt for the surface. I go with her, waving my hand in front of her mask to try and slow her down but not holding her down because I don’t want to panic her any more. At about 10 m she slows down and stops and Dave catches us up. She gives the OK sign and we stop here and breathe the Nitrox 75 for 5 min. We surface and get out to make sure she’s OK, which she is and she decides not to dive again. We then start kitting up again. This time there are no problems as we follow the line down. Viz in the algae bloom is around 5-6 m but once below this it is dark but crystal clear. Viz is now 15-20 m without the need of a torch! The line stops at 46 m and we swim off down the slope, keeping an eye on our maximum operating depth. After our planned 20 minutes we’re back at the shot line and heading up. After our gas switch and a total of 38 minutes, we’re back on the surface as per plan. We drop the cylinders off for filling for tomorrow’s dive and head back to the B&B for the debrief and something to eat. During the evening, Jeanette, Dave’s partner, comes down and we’re the buddy pair for tomorrow as Lesley has decided not to dive. After an interesting evening, listening to Phil Short’s stories, it’s off to bed. The morning is another beautiful sunny one and we’re back for the second dive. This time it’s planned to do a 60 m dive with again a 20 min bottom time and a total time of 71 min.  We’re carrying Trimix 20/30 with Nitrox 65 as a deco gas. We kit up, get in and down the shot and swim off down the slope. We get to just over 61 m, again mindful of our PPO2 and the maximum operating depth. Here we look up and it seems that Dave is just hanging above us, such is the clarity of the water, quite an ethereal experience. Back to the plan and at 20 min we head up to the first deco stop at 38 m. This time we’re ascending in mid-water and just below the first stop I send up the DSMB. The next 48 min we spent ascending and decompressing before hitting the surface at the planned 71 min, only 5 m from the pontoons. A final debrief and another 2 very happy IANTD NORMOXIC Trimix divers are heading back to Bedford. A great 2 days diving at the National Diving Centre!!!!!!!!