Trimix consists of helium, oxygen and nitrogen. Nitrogen is free and pretty much all over the place. Helium and oxygen are available at your local gas supplier. What kind of helium does not matter, just ask for an analysis of the type you have access to, if it is 99.9 percent pure, it does not matter what the designation is.
The purpose of this web site is not to get into how to obtain O2 and He, there are too many regional differences to pigeon-hole this topic. Suffice to say, where there’s a will, there’s a way. A small tip: there are many uses for 02 and He which do not involve scuba diving, such as welding and medical use, and it would behoove you to approach your acquisition from this angle rather than stating outright “I wanna homebrew trimix, got any helium?”.
An excellent reference on this topic is Vance Harlow’s Oxygen Hackers Handbook. The OHH covers information on O2, tanks, laws, designations, etc. The recently released version 3 added info about how to procure helium and detailed info about O2 cleaning. This book is a must have, in my opinion.
O2 cleaning your tanks seems kind of odd to me. After all, why would you want to breath anything out of dirty tanks? So you want to inspect your tanks on a frequent basis to make sure that your compressed air source is not blowing stuff into your tanks. If there is the slightest doubt, then it’s time to break down your doubles and have a look. You don’t have to be a certified tank inspector to unscrew your valve and drop a light into your tank. Dirt, grime and other contaminates can be visually spotted.
As far as O2 combustion is concerned: what I’ve learned over the years is that for a fire to take place you need 3 things: Fuel, Oxygen and Heat. If you remove any one of these three, you won’t have a fire. It is almost impossible to remove all the fuel,which is what O2 cleaning is supposed to do. So lets remove the heat. When filling a tank with O2 you can generate heat by filling your tank too fast. To avoid this, fill your tank very sloooowly. You can do this by opening your valves slowly, using a restricted orifice or a needle valve.
To mix your gases you need some plumbing. The easiest thing to do is to purchase a pre-made whip from Trader John’s , Lloyd Baileys or any other source and save yourself the trouble of piecing one together. A whip consists of an adapter for the tank, a length of hose, a gauge and a scuba tank adapter with a bleed valve. Global Mfg. makes a pre-made whip, part number #45245. The gauge is not a super-accurate type, but combined with an O2 analysis system, it is good enough for our uses. To use an O2 whip on a helium bottle you need an adapter, as the valves are different. Again, you can get this from Bailey’s. If you would like to build one yourself, here is a parts list
Fill ‘Em Up!
The idea is to drain your tank empty, attach it to your He tank, fill it to the required pressure. Then hook up to your O2 tank and add that amount. Why do you add the helium first?
Simple, typically when mixing trimix you don’t have that much O2. Even for a 20/20 trimix you’re only squirting in about 100psi of O2. The needle on most of the analog pressure gauges that are sold out there on O2 whips does not move very well in the first 150 psi range or so. Yes, it may work on some gauges, but for the most part it doesn’t move.
However, going from 700psi to 800psi is pretty much 100psi on any gauge. It’s just the first 150psi or so where the gauge will probably stick. If you throw the He in first, then blow O2 on, the needle on the gauge should already be out of the “problem zone” and you won’t put too much O2 in there.
Since you should already be adding some extra He any way to account for temperature (this is more of an issue when filling helium then gas compressibility, helium being a small molecule heats up REAL quick and you’ll lose a lot more pressure from temperature drops then you will from compression), it’s just the O2 portion that’s the big concern. A fairly good rule of thumb is go a little high on the helium, a little low on the oxygen.
Also helium is more expensive than your oxygen, so it behooves you to get as much out of the He bottle as possible by gassing with it first.
Then test your mix with your 02 analyzer. When working with O2 it is a good idea to throw in a large safety margin. Too much O2 will kill you. Not enough, you hang a little bit longer. What would you rather do? Once you top off your tank with air, test it again.
When it comes time to top off your mix with air and you don’t have a compressor, off you go to the local dive shop. It is recommended that you be up-front with your shop. Tell them you want to top off some mix, therefore it’s important that they don’t drain your tanks and that they have to fill to the pressure you entered into your mix program.
If they give you a hard time, politely let them know that you are more than willing to take your business elsewhere and spend your money at a shop which does not have idiots running it. I have found that if you are loyal to a dive shop, and spend a reasonable amount of dough there, they will pretty much let you do anything you want.
What is the required pressures? There are several mix programs available out there, and there are a couple on this site. There are also several mixing spreadsheets out there for cross-platform use.
Basically they give you the breakdown as to what partial pressure is needed for the mix. For example a dive to 140 with a pp02 of 1.4 and a equivalent nitrogen depth of 100 in a 3000psi tank you would add 377 psi of He. Next you need 317 psi of 02, so you would hook it up to your O2 tank and bring the total pressure up to 694 psi. Then top it off with air. The result is 27% 02, 13% He and 60.7% N2. Or what is referred to as a 27/13 mix.
Helium has a compressibility factor that you might want to consider. Typically you need to add 50-100psi more gas than the charts call for, and some mix programs compensate for this. So if you find your target PPO2 running a little high, this is probably what’s going on.
Dealing With Low PPO2 Mixes by George Irvine
The 2 percent accuracy issue is not too bad when you are partial pressure mixing for middle readings, like 35%, for example. You have to double check the partial pressure and the reading, and the use of the gas is not a problem from either a toxicity or a decompression standpoint.
Where this gets tougher is mixing the real deep mixes, but then the partial pressure still applies and the totals are still valid. The PPO2 are low, so that the amount of O2 added is small. You can start to see where rebreathers, with their small air tanks, can become a problem. The smaller the volume of your mix, the harder to hit your PPO2 mark. A solution to the rebreather problem is to create your mix in a set of doubles and decant into the smaller flasks.
The big trick is to be sure you actually added the gases when mixing, and did not have a valve off while you THOUGHT you added 35 psi of oxygen, or some such number, when in fact you did not, and then the miniox reading, at such low PPO2 seems “acceptable.”
A real good anal way of doing this procedure is what is needed to do it right. Bill Mee and I do it together, and we have a whole checklist to go through before disconnecting the tanks, and for the whole process.
Adding oxygen to a high helium mix can feel like you are adding it when you are not. Just pressurizing a big fill line for a small increment higher, even with a very accurate digital gauge, you can be fooled since you can hear the gas moving even when the tank is not in fact open to accept it – a real dangerous situation. You have to depressurize the line afterwards and note the tank change on the same gauge that the system was on to begin with , and you must do it quickly. There is no way the pressure has risen without the addition, even if the number is thrown off by the cooling – it can not decrease.
Little double checks like that, and then immediately throwing the analyzer on the result will give you some comfort. Then analyze the pure helium to be sure the reading is not offset. A lot of work, but you are always betting your life with this stuff.
-special thanks to the WKPP for help with this subject
Managing Your Gas Supply
A problem with partial pressure mixing is that you will have to turn in your 02 or He tank with quit a bit of gas left in it. For example if you need 20 cuft. of gas for your lowest mixture and you only have 19 in the tank, then you throw away 19 cuft. of 02 or He.
There are several ways to get around this:
Haskel pump- This is an air powered pump where 100psi of air is used to create 4000psi. Essentially a Haskel pump is a great big piston connected to a very small piston. You put air behind the big piston and it pushes the small one. The drawbacks of this unit is that it’s very expensive.
Air compressor- If you have your own air compressor you can feed helium into the intake and let it pump it into your tanks. You can do this with oxygen, but your compressor must be specially prepared for this service, as compressors generate heat. A British method for pumping helium is to attach an old single stage regulator to the bottle, and hook the supply hose to the air compressor intake.
Cascade system- This is where you take several tanks and hook them up via a hose manifold. The idea with a cascade is you fill your tank with the lowest psi tank first then work your way up to the highest psi cylinder. Using this technique you can practically drain your cylinders before turning it in. You can extend your manifold to include the helium tanks if you wish, or you can manually move your whip from tank to tank without the manifold.
?Original Date of Issue: August 1997
Date of Revision: September 1997
?PROOL II – 40
SCUBA DIVING PROBLEMS
May be related to:
1.Barotrauma: (the mechanical effects of pressure change)
*acute vertigo and vomiting
2.Pulmonary Overpressure Accidents:
A.Pneumothorax- “100%”Oxygen-if S/S of Tension – EMT-P’s may decompress
B.Pneumomediastinum – “100%” Oxygen Arterial
*may also present as Seizure, Confusion or CVA
*manage ABC’s as per any patient – “100%” Oxygen
*place in Trendelenburg, 30 degrees head down on their left side
3.Effects of Breathing Elevated partial pressures of Gases:
Decompression Sickness (DCS)
I.Pain Only Bends – “100%” Oxygen and Transport
*triad of substernal pain, dyspnea and cough
*”100%” Oxygen and transport
*may involve any part of the CNS resulting in a myriad of symptoms including pain from spinal cord involvement.
*”100%” Oxygen and transport.
NB: Treatment of patients with above will require a Hyperbaric Chamber – Transport Destination should be decided by consult with On-Line Medical Control.
Home – Rules to Live By ! – Protocols – Procedures
Appendix – Defib – ETI – IV Therapy
EHSNS Home Page – EMC Home Page
The Chamber: Staffed 24 hours a day, 365 days a year, mainly by volunteers, the Catalina Hyperbaric Chamber has treated more than 500 divers since it was first used for that purpose in 1974.
A Ride in the Chamber
When a diver is in trouble, every second counts. Come along on a rescue, from water to boat to helicopter to chamber, as real heroes try to save a diver in danger.
By John Francis
“Ryan Conrad” is a composite of real divers and the MV Adventure is no single dive boat, but could be any. The rescue described here is real, the timetable is real, and the Coast Guard and chamber crews are real.
Your Emergency DCS Plan
The term DCI (decompression illness) includes both DCS (decompression sickness) and AGE (arterial gas embolism). DCS, “the bends,” is divided into Type I and Type II. Symptoms of Type II DCS include numbness, dizziness, muscle weakness, partial paralysis, difficulty walking and speaking, loss of bladder and bowel control, convulsions and unconsciousness.
Aboard the MV Adventure, off Santa Barbara
Finishing his third dive of the day, Ryan Conrad, age 36, and a diver for eight years, climbs up the ladder and staggers to his gear station where he shrugs off his BC and tank. “Yeah, great dive,” he replies to someone’s question. No one notices his slightly slurred speech, his fumbling fingers, his unsteady gait. It’s cold, the deck is rolling and many divers are tired, so Conrad’s symptoms are not immediately apparent. Conrad himself is the last to suspect DCI. Although this was his third 80-foot dive of the day, his computer shows no decompression requirement and his ascent was slow and controlled.
After a few minutes, he notices his left arm and lower left leg are still numb, and are tingling now. Conrad’s left leg buckles and he falls to his knee. His buddy asks, “You all right, Ryan?” with obvious concern in his voice. An alert divemaster overhears.
Tingling and numbness have advanced to cover Conrad’s entire left arm and shoulder, and his left leg up to his hip. He begins to feel pain in his knee and ankle. The divemaster convinces Conrad he needs to lie down and take oxygen, though Conrad still insists that he has probably just pinched a nerve in his back.
The fact that Conrad feels symptoms primarily on one side of his body only makes the divemaster suspect AGE, an arterial gas embolism, despite the fact that Conrad insists his ascent rate was proper. The divemaster reports to the captain, who keys Channel 16 to radio the Coast Guard.
Coast Guard Air Station Los Angeles, at Los Angeles International Airport
Photo by Thierry Girardot courtesy of the United States Coast Guard. Coast Guard Lt. Mike Platt has just put his feet up in the wardroom to watch TV–a Coast Guard Air Station is staffed around the clock like a fire station–when the phone rings in the Op Center. Not the usual telephone sound, but the distinctive long ring of the dedicated Rescue Line from Coast Guard Group Long Beach, the communications and command center. “Uh oh,” he thinks. “We’ve got something.” He zips up his boots and runs to the Op Center where LCDR Joseph Wahlig has already taken the call. Platt hears Wahlig repeating into the phone “… diver … Santa Barbara Island” and keys the mike to loudspeakers positioned throughout the station: “Now put the rescue helo on the line. Now put the rescue helo on the line. Rescue swimmer to provide litter.” Young men and women rush to begin the complex task of putting an HH65A Dolphin helicopter in the air, the urgent “wow-wow-wow” of the rescue alarm filling the huge hangar.
In the center of this space, the Dolphin looks like a tiny orange bug. Its interior is smaller than a minivan. Over the right-hand sliding door is a short arm with an electric winch and 245 feet of 3/16-inch stainless steel cable. In the rear of the cabin is a tiny jump seat for the rescue swimmer who will go down on the cable, and just enough space for what this is all about: a litter carrying a diver in trouble.
Four aircrew members and four mechanics swirl around the Dolphin, intent on their individual pre-flight tasks. One of the station’s three Dolphins is always fueled and ready to go, but there’s more to it than jumping in and turning the key. With a heavily loaded helicopter hovering only 25 or 30 feet over the dive boat, the pilots using nearly maximum power to maintain station, any technical hiccup could be lethal.
Within 20 minutes, Coast Guard Rescue 6584 has received priority clearance from the LAX tower and lifts off between the two runways. Once over the ocean, it turns left, flying at 150 feet to duck under the big jets straining up from the south runway. ETA for Santa Barbara Island is 21 minutes.
Catalina Hyperbaric Chamber, USC/Wrigley Institute for Environmental Studies, Catalina Island
A second call from Coast Guard Group Long Beach has alerted the on-call crew at the Catalina Hyperbaric Chamber. The chamber is staffed around the clock, 365 days a year, mostly by volunteers. Many of them make long trips from the mainland, at their own expense, to keep the chamber operating.
Today, chamber director Karl Huggins and chamber technician Lorraine Sadler are on duty, as are volunteers John Sayer and Walt Schob. Sadler takes the call on a dedicated emergency line to her portable phone. Immediately, she calls the Medical Alert Center in Los Angeles County, which will scramble the on-call hyperbaric physician for a quick flight to Catalina Island. Next on her checklist is a call to the L.A. County Lifeguard paramedics at Isthmus Cove, only a few minutes away by boat or car. They will be on hand to take over emergency medical care from the Coast Guard until the doctor arrives. Next, Sadler calls the rest of the crew, who remain within 20 minutes of the chamber at all times when on call. Finally, Sadler calls the sheriff’s deputy assigned to Isthmus Cove. If this proves to be a fatality, there will be reports to file.
Each of the chamber crew has a checklist of work to be done to get the chamber on-line. The fire control system is activated and checked. Fire danger is small but taken seriously given the high oxygen pressure in the chamber, so inside the chamber are six overhead sprinklers and a fire hose. Various valves on the chamber operations panel, the chamber blow-down panel and the BIBS gas panel are opened and closed. Pressures are checked as the high-pressure storage banks come on line. The building begins to vibrate and shake as the big Ingersoll-Rand compressor whines into life. Meanwhile, Schob, acting as the tender today, lays out the IV kit, cardiac kit, airway kit, pulse oximeter and EKG/defibrillator next to the gurney where they’ll be handy to the paramedics. The diver is now about 30 minutes away.
MV Adventure, Santa Barbara Island
Aboard the dive boat, antennas and masts that might be hit by rotor blades have been lowered. The other divers have hurriedly packed their gear and are inside the cabin, out of the way and out of the 100-mph rotor wash.
LCDR Wahlig holds the Dolphin about 30 feet over the boat’s aft deck while rescue swimmer Tom Bolin clips onto the cable. Flight mechanic Pat Hirst conns the helo closer–”forward and right 40, forward and right 30″–and lowers Bolin toward the boat. This is tricky: a random air current or a freak wave could smash Bolin against the steel boat. But this time he reaches the deck safely. Next comes the litter, a padded steel cage. Then Bolin goes below to meet his patient while the helo moves off a safe distance.
After breathing oxygen for an hour, Conrad feels much better. At the same time, he no longer denies the obvious: that he’s in serious trouble. Everyday worries about his job, his family and the car that needs repair have been swept off his mental desktop. He is entirely focused now on one thing: getting well.
Bolin sees the anxiety in Conrad’s eyes, and in order to calm him a little, he explains in detail what will happen next. Bolin straps him tightly into the litter along with a small oxygen bottle. Wahlig brings the helo over the deck again. Hirst drops the cable and reels in first the litter, then Bolin. The helo is away for Catalina Island 24 minutes after arrival on scene.
Helicopter Pad, Catalina Hyperbaric Chamber
Just two hours after climbing out of the water, Ryan Conrad arrives at the hyperbaric chamber. He is transferred to a gurney and wheeled into the adjacent hangar that houses the chamber, while Coast Guard Rescue 6584 lifts off for the flight home.
Meanwhile, paramedics have begun giving Conrad physical and neurological exams. Until the hyperbaric physician