In the past, nitrox was considered the ‘devil’s gas’ but today it is in common use amongst divers and trimix has replaced it as the new ‘devil’s gas’!

After completing the Accelerated Decompression Procedures course and Buoyancy Workshop, a small group of club members continued with the Sports Mixed Gas (SMG) course. On successful completion, this allows a maximum dive depth of 50m with up to 20:30 split of oxygen and helium.

The benefit of SMG is to avoid some of the effects of narcosis by diving an equivalent narcotic depth of 30m due to the replacement of nitrogen with helium in the breathing gas.

Following classroom sessions, the Bracknell Sub Aqua Club divers set off for the NDAC – ironically it was halloween! They spent 110 minutes on a dive carrying out drills in preparation for two deep trimix dives to 50m and 40m the next day.

The SMG course does not use BSAC tables but divers plot their own run time tables with PC programs such as ‘pro plan’. A copy of the plan is taken with them on the dive.

advantages of trimix

• deep diving gas – safer than air
• a 50m dive that you can remember in detail due to a narcotic depth of 30m.

disadvantages to manage

• light gas, need to manage off gassing
• transfers heat very efficiently (cold when put in a dry suit)
• not a cheap gas combination.

More information about the Sports Mixed Gas course can be found in the training section of this website.

This article was first published on pages 8 – 9 of mouthpiece newsletter Summer/Autumn 2009 edition.