QUESTIONS? CALL 0121 288 2233

Phil Grigg Technical DivingPhil Grigg Technical Diving

Phil Grigg Technical Diving

Phil Grigg Technical Diving Provide Open and Closed Circuit Technical Diver Training & Support

T 0121 288 2233
Email: [email protected]

Phil Grigg Technical Diving
Midlands, United Kingdom

Open in Google Maps
  • HOME
  • ABOUT
    • About Phil Grigg Technical Diving
    • Diving Services & Project Support
    • Reviews & Testimonials
  • TRAINING
    • IANTD OC
      • IANTD Nitrox Diver
      • IANTD Recreational Trimix Diver
      • IANTD Deep Diver
      • IANTD Advanced Nitrox Diver
      • IANTD Advanced Recreational Trimix Diver
      • IANTD Technical Diver
      • IANTD Normoxic Trimix Diver
    • IANTD SIDE MOUNT
      • IANTD Side Mount Diver
      • IANTD Advanced Nitrox Side Mount Diver Combined
      • IANTD Advanced Recreational Trimix Side Mount Diver Combined
      • IANTD Normoxic Trimix Side Mount Diver Combined
    • IANTD CCR
      • IANTD Closed Circuit Rebreather Diver
      • IANTD Closed Circuit Normoxic Trimix Diver
    • OTHER
      • IANTD Nitrox (EANx) Gas Blender
      • IANTD Trimix Gas Blender
      • Rebreather Try Dives
      • Diver First Aid Courses
      • Advanced First Aid For Divers
  • SCHEDULE
  • EQUIPMENT
    • Closed Circuit Rebreathers
      • VMS Sentinel RedHead CCR
      • Inspiration Closed Circuit Rebreather
  • BLOG
  • CONTACT US
  • Home
  • Technical Diving News & Opinion
  • Is 10/52 Always the Best Diluent?
24th January 2021

Is 10/52 Always the Best Diluent?

Is 10/52 Always the Best Diluent?

by Phil Grigg / Friday, 26 December 2014 / Published in General, Training
10/52 In A Diluent Cylinder

When venturing beyond the typical air diving range on a rebreather a trimix diluent must be used.  However, because a rebreather effectively blends the gas mix on your back to turn it into a better mix to breath, divers have a tendency to just reach for the same diluents. One of the favourites is a 10/52 trimix.

I was recently shown an incident report where a diver appeared to have lost conciousness on or near the surface.  While I’m not going to speculate about the reason why (the report was, as usual, vague on details) one of the potentials listed was the choice of diluent.

Why 10/52?

One of the main reasons 10/52 is a popular choice for rebreather divers is that it has the number 10 in it.  That might sound a bit odd, so for those of you who aren’t rebreather and / or trimix divers I can explain….  One of the principle skills a rebreather diver uses in fault finding and / or problem solving underwater is to flush a known gas mix into the rebreather to replace the gas they are currently breathing.  To be able to do this, it’s handy to know the partial pressure of the gas that is to be flushed in.  As I’m sure you can all recall, this is calculated by multiplying the fraction of oxygen in the gas by the pressure at your current depth.  If the fraction of oxygen is 0.10, the it makes the calculation very easy to perform at any point during the dive.  The PO2 of the gas at 55m say would be 0.65.

10/52 is also what is known as a HeliAir.  It require no additional oxygen during the blending process, just helium and air.  This can make the blending process a bit simpler.

So It Sounds Like a Good Gas to Use?

Phil Diving a Sentinel with Multiple Stages

Phil Diving a Sentinel with Multiple Stages

In simple terms,  it does.  But it’s not always the best gas to use.  In the above example the PO2 at depth of 0.65 is well below the 1.00 limit we usually aim for.  The final mix being breathed would be around 20/46 making it feel like diving to less than 20m on air narcosis wise.  The big problem with this mix though isn’t on the bottom, it’s nearer the surface.  Sat on the boat deck, the PO2 of this gas is 0.10. Dangerously low.  In fact is doesn’t start to make it from dangerously low to just low until gone 4m.  This means that the diluent can’t be breathed directly till below 4m.  Any Bailout Valves can not be used / tested and great care must be taken when using an Automatic Diluent Valves.  A large quantity of oxygen must be added to bring the PO2 up to the typical low set point of 0.70 in these shallow areas, and any addition of diluent is going to cause a dramatic drop in PO2 within the breathing loop.

What Else Could We Use?

Using the same 55m dive, my choice of diluent would be 14/44.  The PO2 of the diluent is still less than 1.00 and the end mix being breathed would be around 20/40, which still gives an equivalent narcotic depth of just over 20m this time.  There are also off the shelf deco tables available for 14/44 and for 19/40 (which would be an ideal bail out gas).  The plus side of using 14/44 is that should I need to add diluent to the loop on surface (say swimming to the shot) I can do so with much more safety.

So Should We Stop Using 10/52?

No, probably not.  But what more divers should start doing is think about their choice of diluent rather than just reaching straight for the 10/52.  It’s not always the best gas available.  Even if you can’t be bothered to work out the best mix (you really should be!), most dive planning software will do it for you now.

But What if The Dive is Cancelled?

I can say there is at least one reported incident involving a diver using 10/52 on a dive that didn’t require it (see DISMS Incident Report).  If the dive get’s cancelled and you end up doing a different depth, think about getting your diluent re-blended.  Ditching half the contents and topping the remainder off with air gives a diluent that is now safe to breath on the surface.  Even a whole 3litre cylinder of 10/52 is only around £10 in cost, hardly a bank breaker.

Just remember, the best mix for the dive isn’t always going to be the one you already have in your cylinder!

« Previous - Technical Diving Coaching For Individuals
Next - Breathing Rates in Emergency Situations & Bailouts »
  • Tweet
Tagged under: CCR, Diluent, Dive Planning, Trimix

About Phil Grigg

What you can read next

Unknown Torpedo Carrier – Diving In Lebanon Part 4
Open Circuit DSMB Deployment Featured Image
Up & Coming Availability
NISD In Beirut Harbour Featured Image
Diving in Lebanon – Part 1

FOOTER MENU

  • Home
  • About
  • Training
  • Equipment
  • Blog
  • Contact Us
  • Links
  • Site Map
  • Terms, Conditions & Privacy

GET IN TOUCH

T 0121 288 2233
E [email protected]

Phil Grigg Technical Diving
Midlands, United Kingdom

17 days agoRT @NDAC_co_uk: With the country in lockdown we've closed the National Diving & Activity Centre for all activities until April. We plan to…
Follow @@phil_grigg
  • Tweet
  • GET SOCIAL

© 2015 Phil Grigg Technical DIivng

TOP
This website stores cookies on your computer. These cookies are used to collect information about how you interact with our website and allow us to remember you. We use this information in order to improve and customize your browsing experience and for analytics and metrics about our visitors both on this website and other media. To find out more about the cookies we use, see our Privacy Policy Read More.

If you decline, your information won’t be tracked when you visit this website. A cookie will be used in your browser to remember your preference not to be tracked. Further cookies may be set if you use our store features or to provide anonymised information to help us improve functionality and user experience.

Cookie settingsACCEPT
Privacy & Cookies Policy

Privacy Overview

This website uses cookies to improve your experience while you navigate through the website. Out of these cookies, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. We also use third-party cookies that help us analyze and understand how you use this website. These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. But opting out of some of these cookies may have an effect on your browsing experience.
Necessary
Always Enabled

Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information.

Non-necessary

Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies. It is mandatory to procure user consent prior to running these cookies on your website.