The Wonder Breathing Gas - Trimix

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Helium from a tidally shredded star being expelled from a black hole
 Credit: NASA; S. Gezari, The Johns Hopkins University; and
J. Guillochon, University of California, Santa Cruz  

Fred Stratton
Instructor and Technician
fred@bubblesornot.com

TECHNICAL DIVING SERIES PART IV

Helium's atomic weight and number
Credit: Greg Reese on Pixabay
Most people think of the Goodyear blimp and party tricks when they think of helium. Commercial and technical divers embraced helium decades ago as a means to diminish  nitrogen narcosis and oxygen toxicity beyond recreational depth. To trimix divers helium is a miracle gas that opens a vast realm of new adventures unattainable on air. 


Astronomers discovered helium by noting a yellow spectral line signature during a solar eclipse in 1868 and named it after Helios, Greek god of the sun. Helium is the second most abundant element in our universe after hydrogen although it is rare on Earth comprising only 0.0005% of planet's atmosphere. Helium is obtained primarily from underground deposits in Oklahoma, Texas and Kansas. 
Add helium to oxygen and nitrogen and 
you get Trimix (He, O2, N2)!
 Photo: PADI 

Many magnificent wrecks and fascinating flora and fauna lie beyond 165 feet. Graduating from a Tec 50 course equips us with knowledge, skills and abilities to take the next step in safe deep diving by adding helium to our breathing gas. 

 As we descend beyond 165' (50m) elevated partial pressures of oxygen (PPO2) become a concern due to the risk of central nervous system (CNS) oxygen toxicity. Using helium to displace some nitrogen enables us to reduce our equivalent narcotic depth (END) to less than 130' (40m). Blending a hypoxic mix - less than 21% oxygen - we drop our PPO2, thus reducing the potential for CNS O2 toxicity. 

A few people still dive to 200' (62m) and deeper on air...but why risk severe narcosis and CNS dangers when learning to plan and execute deep adventures with trimix awaits you at Bubbles or Not. Welcome to the Tec Trimix 65 course. 

PADI TEC TRIMIX 65 COURSE

Carrying around 1,600 cubic feet of gas, (L-R) Dan, Dom, JD
and Bob are well provisioned for a deep technical dive
Photo: Rose Bennett
Tec Trimix 65 takes you beyond your Tec 50 experience by introducing you to the first stages of full technical deep decompression diving. Certified Tec Trimix 65 divers are qualified to make multi-stop trimix decompression dives that employ EANx and oxygen for accelerated decompression, and trimix with 18% or more oxygen as bottom gas.

Trimix 65 qualifies you to:
  • conduct open circuit dives on trimix with 18% or more oxygen to a max depth of 210' (65m) with a PPO2 of 1.4 or less and an Equivalent Narcotic Depth (END) of 130' (40m).
  • use two decompression gases / cylinders for trimix dive
Tec Trimix 65 is a sub-course of the Tec Trimix Diver course which certifies divers to use trimix and up to four decompression or stage cylinders during dives to 300' (90m).


Using Trimix to get your Deep Fix


USS ORISKANY conducting flight operations
in 1955
Photo: US Navy 
Last month we (virtually) dived the Essex-class aircraft carrier USS ORISKANY (CV-34) where she rests in 212' (65m) of water south of Pensacola, Florida in the Gulf of Mexico. We limited ourselves to the top of the hangar bay flight deck at 165' (50m) with our Tec 50 certification. 

Now what we are Trimix 65 certified and have experience diving to 210 feet we can explore the entirety of the ORISKANY down past the hangar bay and gun emplacements to the giant propellors and the keel! It will take dozens of dives to grow weary of this glorious warship. 

Properly labeling scuba cylinders is
an unbreakable rule when diving any
gas other than air
Photo: Fred Stratton
The Canadian-flagged ore carrier Roy A. Jodrey plied the Great Lakes and Saint Lawrence Seaway until 1974 when it struck a buoy near Wellesley Island in Alexandria Bay, New York puncturing her hull. The crew ran her aground near the U.S. Coast Guard startion attempting to save her but the pumps couldn't keep up. 

The Jodrey sank on 21 November. All hands safely went ashore. The Jodrey rests in 254' (77m) while her bow starts at 145' (45m). This is a spectacular technical dive on a historical wreck that rests at an angle akin to an air-to-air missile on a launcher; most wrecks rest horizontally.



U.S. Navy carrier aircraft decimating the Japanese
Fleet during Operation Hailstone
Credit: US Navy photographer aboard USS Intrepid (CV-11)
National Archives photo 80-G-215151

The Pacific paradise of Chuuk (Truk) Lagoon was the scene of Operation Hailstone which sank dozens of Imperial Japanese ships in February 1944. The San Francisco Maru's deck starts at 158' (48m) and entices divers with war relics such as sea mines, tanks, artillery shells, torpedoes, beer bottles and porcelain. 

Construction equipment rests next to the hull at 205' (62m) making the San Francisco Maru a perfect Trimix 65 site to explore. 

The government of the Federated States of Micronesia forbids artifact retrieval from these war wrecks. The ships appear as they were sunk 75 years ago, a time capsule of great loss for Japan and an American success toward ending a global conflict. 


What You'll Learn and Do during Tec Trimix 65 

100% O2 enables accelerated decompression at 20' (6M)
and 10' (3m) stops and requires O2-cleaned regs
Photo: Dive Rite

Practical Applications

  • Check diver equipment configurations
  • Establish a spirit of team building and comraderie
  • Develop fluency with using multi-gas planning software
  • Build upon mission planning skills learned and practiced in the Tec Deep Diver Course
  • Build planning skills for Trimix dives including detailed mission planning 
  • Plan dives that include accelerated decompression
  • Final dive planning will be the students' responsibility with staff oversight and assistance

Five Open Water Dives

  • Dive 1: max depth of 30' (9m)
  • Dive 2: between 90' (27m) and 165' (50m)
  • Dive 3: between 100' (30m) and 165' (50m)
  • Dive 4: between 100' (30m) and 185' (56m)
  • Dive 5: between 150' (65m) and 210' (65m)

JD Walters get his dive face on prior to a
deep technical dive
Photo: Rose Bennett

Open Water Skills

  • Normoxic accelerated decompression
  • Respond to a runaway low pressure inflator
  • Simulated loss of deco gas 
  • Descent check
  • Conduct long hose swim with buddy 
  • Remove & replace deco bottles without a mask
  • Respond to an unresponsive breathing diver at surface
  • Valve shutdown & regulator switch to address freeflowing regulator
  • Primary BCD failure, neutral buoyancy with backup system
  • Deploy lift bag or delayed surface marker buoy (DSMB)
  • Switching gases using multi-gas computers
  • Gas/depth/time awareness - record depth, time & SPG reading each 15 minutes throughout the dive
  • Gas switch to O2 at 20' (6m)
  • Air break - switch from deco mix to back gas then back to deco mix
  • Post-dive review and critique

To Enroll in Tec Trimix 65 You Will Have

  • Earned your Tec 50 Diver certification
  • Logged at least 100 dives

Additional Reading

Years before Trimix, divers experimented with a helium-oxygen mix. Divers used Heliox for the first time in 1925 to investigate why the 280-foot steamship the Lakeland sank in Lake Michigan during a winter storm. Read about the Wreck of the Lakeland and the Birth of Mixed-gas Diving in DAN's Alert Diver magazine. 

Coming in July: Manmade Scuba Playgrounds 

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