Monday, March 30, 2009

Medicine and the Technical Diver

By Gerhard du Preez.

It is a human trend to grab for medicine any time a problem is perceived with regard to their health. Divers are no different! We self medicate for something as simple as a blocked sinus (which prevents the diver equalizing properly) to something as common as seasickness, never mind drugs required to compensage for muscle aches and pains from the lugging heavy cylinders or over doing it in a current.
But are we really paying attention to what we put into our bodies ? The Technical diver is even more prone to the horrible side effects drugs can produce during a deep dive. These side effects are affected by depth, longer exposures and higher partial pressures of oxygen. Did you know that some of the drugs for prevention of seasickness for example contain a very high dosage of an ingredient that is used for sleep medication and is at almost the correct dose as prescribed for insomnia! Now you go diving on that, dealing with narcosis and all sorts of fun side effects start to kick in and complicate your dive.

Speaking to your GP is usually not the best answer - you must discuss this with a diving physician that actually understands what an increase in ambient pressure does in combination with excessive exposure to Oxygen.

So what to do until you get that brilliant opportunity ? Well, there are two specific things I want you to look at, the sympathetic and parasympathetic nervous system and their response to drugs and diving. These are the most important systems when it comes to predisposition to oxygen convulsions and of course narcosis and mental slowing. My advice is to read the pamphlet that came with your over the counter meds for a change!

What happens when a drup affects the sympathetic system ? The sympathetic nervous system is in essence the “ fright and flight” response that puts the body under strain as it immediately prepares the body to go into self defence mode. The heart rate increases, breathing rate increase, pupils dilate to let in more light so you can see better, blood get channelled from less needed organs to the vital ones, brain, heart, kidneys etc. The result is a dry mouth as saliva secretion takes a back seat as there is no need for gastric juices to digest food at this point. When a drug affects the sympathetic system you as a diver can expect to suffer a severe increase in susceptibility to Oxygen Toxicity and the all feared oxygen convulsion. Avoid drugs that STATE : Increased heart rate, increased blood pressure, dry mouth, photophobia, tremors etc. Especially do not take it if it clearly states “ do not operate heavy machinery while taking this medication” . It is a tad stupid to put it mildly to go diving with any drug with these types of side effects after reading this. These are very, very common side effects and every diver should be aware off them and NOT use those drugs.

The parasympathetic system is what I like to refer to as the “ stay and play” one. The body prepares to basically go to sleep or shut down which is the reverse of the sympathetic nervous system. Your central core relaxes, the heart rate goes down, breathing slows down, more gastric juice gets excreted, pupils constrict and become smaller as the body starts going into energy saving mode. This fits the category of most antihistamines and especially seasickness prevention medication (stuff like dephenhydramine etc). So look for side effects that cause drowsiness, dizziness (usually associated with the fact that you blood pressure is dropping), an increase in salivation etc. Meds that you suspect are affecting the parasympathetic nervous system increase narcosis and when diving with high partial pressures can result in blackouts.

OTHER INDICATORS : There are a few more side effects that warrant mentioning.

- Drugs that have anticoagulation properties (like warferin that thin the blood) will cause excessive bleeding etc.

- NSAIDS ( non steroidal anti inflammatory drugs). Those brufens you are popping cause an increase in blood pressure so be careful as the immersion effect already causes an increase in you cardiac preload and thus your blood pressure.

- Drugs that cause an increase in urination frequency, including and not limited to blood pressure control medications. These will increase your risk in DCS. And the list goes on.

Thus in summary and as a rough guide, if you are unsure ask the pharmacist if the drug has any effect on the sympathetic or parasympathetic nervous system, if the answer is yes, then do not use it prior to diving.

Before I finish, I would like to give special mention with a suggestion of an alternative medication:
- Decongestants – rather try a nasal spray as it is more site orientated and not as systematic in action.
- Sea Sickness prevention- Ask your doctor about epanutin, a drug prescribed mainly for prevention of epilepsy that was found to be very effective against sea sickness.
- Anti-inflamatories, antihistamines and other substances need to be used in moderation. Think if it is really warranted or could you rather do without for now.

Remember this is just a rough guide to assist you in making a quick decision when looking at the drug solely from a diving safety perspective. Do not stop using any chronic medication without consulting your doctor.

Safe Diving

Wednesday, January 7, 2009

Rebreather Cells - the Saga Continues

Welcome back and I hope everyone had a fantabulous new year! We had a brill time...and learnt that snorkels are CRITICAL gear. Yes, we found the wading depth of my Ford F250...and then spent a fascinating 1.5hrs finding out where the water went and how to get it out! With beer, a stunning river view, hippos and thankfully no lions. But back to diving :). Gerhard has this to say:
I have had a few comments after a recent article published in a local diving magazine in regards to the "rolling" of cells for re-breathers.
You need to understand one thing. In my opinion if the manufacturer recommends something then it might be a good idea to follow the recomendation, regardless what your own opinion on the matter may be. If for no other reason than the fact that they built the unit and therefore know a whole lot more about it than any diver could (no matter how many hours have been spent on the machine).

Rolling (of the cells) is an old concept that tech divers have been implementing not only with cells but with other bits of gear as well. Back before equipment was reliable (ok, so that statement may still stand the test of time) we used to "roll" everything from flashlights to batteries.

For example , I dived a backup light from 2 different brands, the batteries were from different manufacturers and were changed prior to any hectic dive or after any dive if they were found switched on or if used simply because reliability on these items was questionable. Reliability is the very reason I do not use re-chargeable batteries in my re-breather controllers - they have a different voltage curve and you can get into trouble. Instead i use alkaline or lithium type batteries.

Interestingly enough we teach our students to roll their controller batteries but yet advocate not to roll the most questionable part on the unit - namely the cells ?!? Sheesh. If the batch has a fault you just shot yourself in the foot and yes there have been some batch issues. You never know how that cell was stored up to the day you got it. It is considered to be the most unreliable part of your unit and also the most important one in regards to staying alive.

To my knowledge the following manufacturers advocate very publicly and loudly that you roll your cells:
- Juergens Marine (Hammerhead), Dive Rite, AP Valves (Inspiration) as well as Megladon.

The choice is yours. Get cell validation or get true voting logic but the only way to achieve it is to roll the cells as the parameters will be different when compared to replacing all the cells all at once ...... and having what is called a "false positive" that might just make your 3 horses turn out to be 3 donkeys.

Keep safe...and keep diving :)

Wednesday, December 10, 2008

Blending Roles and Responsibility

Recently we heard yet another blending horror story. A rebreather diver dropped his oxygen cylinder off to be refilled on site, picked it up and decided to check the contents... to discover that it had been filled with 50% oxygen and not 100%. A potentially fatal mistake. He did the right thing, he analysed his gas...but too often divers abdicate responsibility and just assume that the blender knows what they are doing. They trust their lives to someone else...which is something I have an issue with.
So, what are the roles and responsibilities between diver and blender ? The rules and regs are simple enough. The diver is responsible for analysing his gas when he receives it. The blender is responsible for ensuring the person filling has completed an official blending course (including the exam) and that the diver signs for his gas.
The problem is that we all get to blase about it...and stop following the process. It is a pain for the blender to complete a log, the divers complain about the delay... and invariably blending is delegated to a low ranking employee who may or may not have the proper, official qualifications. All round it is a disaster waiting to happen.
Diver do not make it easier either. We had the instance the other day with a new client arriving to have Trimix fills. It was a bit of a last minute thing (as it somehow always tends to be). When Gerhard examined the tanks he discovered they did not have any markings indicating that they were oxygen cleaned. G phoned the client asking what the status was. The client was a little annoyed... what was the problem ? G explained that we do not fill cylinders without oxygen cleaning and if we do not know the tank, we will oxygen clean them ourselves to make sure. His reply, what is the problem ? It is only a small amount of oxygen you are adding. I started to have a small fit. Why ?
Well last year we had a small oxygen explosion, from a cylinder that we knew and trusted. Gerhard walked away slightly deaf and with a nasty burn on his arm. Did I mention that this was a cylinder with all its paper work and a diligent, trusted owner ?
The long and short of it was that the client was told that if he wanted us to fill his cylinder he would have to get them oxygen cleaned, either by us or someone who was qualified. For some reason he battled to grasp the concept that his R40 nitrox fill (ok, there were some more expensive trimix fills as well) was not worth Gerhard's life. And that is really what it boils down to.
As divers we do not want to be bothered with rules and processes. So here are a couple of things you can do to make the system work

1) Have your paperwork. Cylinders that are nitrox filled or trimix filled need to be oxygen cleaned by a reputable vendor

2) If your cylinders are filled at the coast they require an oxygen clean before you fill them with nitrox or trimix again. In fact, if you are filling with any sport shop you should get them oxyen cleaned before using them for mixed gas again. Simply put, clean gas is not easy to find and it only takes a small amount of oil to kill the blender.

3) Give the blender time to fill your cylinders. It can take 2 hours to do a Trimix fill and the more rushed the blender is, the more chance for errors

4) INSIST on signing for your mixes when collecting them from the blender and ALWAYS ANALYSE even if it is pure oxygen. If the blender is reluctant for you to sign remember he is legally bound to perform this check and if he still has no mechanism in place... create your own paperwork. If something goes wrong on the dive the first thing that will be examined is the mix in your cylinders... and it starts to get ugly when fingers are pointed at the person who the person who placed the cylinders. So why not avoid the whole ugliness/

5) Take your own life seriously. Is it worth R40 (a nitrox fill), R500 ( a trimix fill ) ????


Apologies. I suddenly realised it was the 5th of November last time I wrote on the diving blog. Firstly, a question for ya all...what questions do you have that you would like answered (preferably on technical diving). We do have some items scheduled for the New Year starting with a look at the different gases...

Lastly, I would like to wish everyone a spectacular festive season. We are off to the bush for three weeks and the blog will resume in the New Year.

May the bubbles be kind to you :)

Wednesday, November 5, 2008

The Skinny on Disinfectants

This blog is for those of you on rebreathers! Historically in South Africa we use Buddy Clean to disinfect our machines, the question is, is this the best choice ? I have taken the content of this blog from the ANDI manual on rebreathers. Their content in turn is based on a study conducted by the Department of R&D, Canada in 2002.
The study had two criteria that had to be met for a product to be recommended for use:
1) The product had to exhibit an absence of components that would case undue risk to human health during use that could not be prevented by reasonable protective measures
2) Proof had to be available that the disinfectant was effective
Interestingly, the report showed that 7 products commonl used were unacceptable. These were:
- Buddy Clean (gulp)
- Confidence Plus
- Sanizide Plus
- Advance TVE
- Bi-Arrest 2
- Cavicide
- Listerine Antiseptic
Only two products were found to be fully acceptable, Virkon S (the product of choice) and Trigene II. Unfortunately at the time the study was released there was no version of Virkon available for human use (its origin is agriculture). There is now Virkon (without the S)
Some info on Virkon:
- It has been extensively tested and proven tot be a broad spectrum disinfectant, considered bactericidal, virucidal (both enveloped and non-enveloped), fungicidal and a tuberulocidewhen used at its intended working concentration of 1% for a min soaking time of 10 minutes.
- It comes in a number of package sizes.
- It is no deactivated by detergents or hard water, but may leave a residue if recommended decontamination procedures are not followed
- If used as prescribed, it is not deleterious to the health or equipment of divers and is effective against almost all microorganisms to which a diver may be exposed.
- Extended soaking of metal objects may cause corrosion/ damage and deactivation of the product more quickly (recommended soaking time is 10 minutes).
- A 1% solution is table for a week.
- Good infection control practice indicates that disinfectant solution should be changed daily, but this is unnecessarily wasteful. If the solution loses colour within the subsequent 7 day period it should be replaced
Interestingly ANDI and Juergensen Marine recommend a standard solution of 1% beta-dine solution for disinfecting.
If you are looking for alternative, here is the list recommended by ANDI (in order of preference)
- Virkon
- Virkon S (the agricultural version)
- Trigene !!
- Microban Disinfectant Spray (an ANDI product)
- Commercial Hospital Use disinfectant solution such as Beta-Dine 1
- Buddy Clean
- Alcohol
- 10% Bleach Solution
- 50% Vinegar, 50% water
Based on these findings, Liquid Edge is importing Virkon and it is way more affordable than our usual products. Try one tablet that makes 0.5 litre for R30!

Friday, October 24, 2008

The Truth About Cell Calibration

This is written by Gerhard...for all those rebreather divers out there (and especially those who have been following the recent reported, alleged, near death on an inspo). If you have any questions....mail G at :)

First things first: cells becoming current limited is a huge reality, can happen for sure! Remember they are one of the weakest links in your re breather. So what to do....

Looking at how the unit calibrate:
When you hit the "yes" button, the display you are looking at is the milivolts divided and measured against air in Oxygen. So to give you an example , one for altitude , one for sea level.

Sea Level: assume ambient 1 bar. Air= 0.21 , O2= 100% Calibration starts and the displays read : 1.02 1.00 0.96 What the unit does now is compare the mV reading to air whilst being in O2 , thus ACTUAL mV will be the following:
1.02 will be basically 10.2mv (thus the inspo now uses a set MV for start calibration assuming about 4.7- 021/100% oxygen- as its linearity checking) so the real MV of the cell submerged in O2 will be 10.2 mV * 4.7 = 47.94 MV , and that would ASSUME the start up MV was 10.2 as well ( It assumes Cell linearity is constant) NOW if you kick the lid off and measure cell 1 with a mV meter and do NOT get a reading of 10.2mV in air.... oops then the assumed linearity is incorrect....more about that later!

The Cell should be kicked out if it falls below 8.3mv approx (39.01mV)

The Hammer boots out ANY cell that does not make 40mv actual as it is predicted to become current limited(including at altitude ,which is a

At altitude the same applies EXCEPT that you must take the MB reading into
Thus if your reading is 0.89 0.88. 0.91 at altitude with a 850mb reading then just multiply the resultant by 0.850 to take it to "altitude"
Thus cell on will be 8.9mV * 4.7 / 0.850 = 49.2mV SEA LEVEL , or 41.83 Altitude reading- good stuff.
So even if you do not see a 1.00 when calibrating at altitude it does not mean the end of the world. According to your altitude it should be fine (above 40mv) SO if you work out the actual MV and see it is below 40mV actual for the altitude regard it as suspicious

NOW what I do NOT like is the fact that it works on a constant linearity assumption when you calibrate( 100% / 21%=4.7). So if you look at an actual as in the hammerhead you have the following:

At sea level my cell mV read in air : 10 9 9 After dousing it in pure O2 for calibration they all stabilize at 39 48 43 mV respectively.
That means that the ACTUAL linearity is as follows :
Cell 1 - 3.9
Cell 2 - 4.8
Cell 1 - 4.3
Thus you can see that it is NOT an actual constant and also cell 1 that seems high did not actually make the calibration and is now booted out as a possible limited cell, but the inspo will calibrate this cell as acceptable (borderline but there) esp if you told it the O2 content was 98%......

At altitude I expose the head to air to see the PO2 shown to verify air:
The mV reads 10 9 9
The Po2 I expect to see is .21 * 0.850 mb = 0.178 PO2 actual that the handsets should display.
All cells displayed within that range since previous calibration.
I wrote down my mV in Oxygen from the previous dive which was 39 48 43
Thus at altitude with pure O2 I expect to see a PO2 of 0.85 shown for each cell.
They all get very close to it.
You can then look at the linearity from each cell then vs now.

So cell 1 is 39/10= 3.9
Cell 2 is 48/9= 5.3
Cell 3 is 43 /9= 4.7
If you calibrate now and all values are still within that linearity level the cell is shown to be constant within calibration range. So if you DID fitness test the cell on the previous dive at 6m and it passed and now linearity check and mV seems stable the cell in theory should not be a problem as it's linearity range did not change (you can only hope!)

Also , in theory it also this tells us is that the cell showing highest linearity should be the most accurate in response range as it can read over a finer scale , no it does not mean it might not be limited, it just tells me the response range is the widest. It is like looking at a 300bar gauge vs a 400bar gauge. The 300 bar gauge will show clearer needle movement across the board as it uses a finer scale. You can see 2bar movement more clearly on the 300bar one than on a 400 bar gauge. So I would expect cell 2 to react nicely during flushes and O2 additions with cell one maybe a bit slower.

Use an approach where you can see yourself what the actual mV in air and actual PO2 is in air in regards to the previous calibration, and once the unit or cells are flooded with O2 then you can record that mV and PO2 shown BEFORE calibrating again. If the linearity is within the same limit the cell should perform in the same fashion ,esp if it is a few months old. You will at some point have 3 new cells in your unit ,it is unavoidable sometimes , but they need to be checked vigilantly esp in the first month. The hammer you can also leave flooded with O2 and come back after a while and look at the ACTUAL mV of the cells to see if there is any deterioration in the actual voltage. If there is , flood with O2 again, if the cells do not come back to previous max mV then get worried! The only way to test if it is current limited is to actually pressurize the unit on the surface or dive to 6m then spike it, deeper would be great. Problem is you do not want to start a heavy dive with an O2 spike through the lungs;-) But you can always go O/C , flush at 8 or so meters while manually manipulating the lungs to try get O2 cycled , look at the readings , then flush again and get on the loop and continue the dive.

Now this all sounds very good , but lets get back to the BUT... There are two options, one is single point calibration- so we use high o2 or 100% O2 to calibrate the cell, OR we try 2 point calibration, so we assume x linearity in air and x in O2 and draw a line, sounds good...and here is the BUT. Cells are NOT linear, they have a curve! The further away the maximum or minimum extends the worse the curve slopes, so your most accurate reading is the CLOSEST POINT TO CALIBRATION. In other words, if you calibrated at sea level- Po2 1 - then your most accurate readings should be in the 0.7-1.3 vicinity, if you calibrate at altitude- Mb 850- then all cells read Po2 0f 0.85.... hmmm...then reaching 1.3 is that little bit harder... Remember cells are usually within 2% error margin of calibrated value, so the only solution to check high end readings is to test the cell in a hyperbaric scenario. 2 Point calibration is not helpful either as I showed you with the hammerhead cells in air and O2 as the actual linearity differs, and as explained on a single point calibration you have a higher reference point from which to work, thus a smaller error!

Next option- Have cell verification like what was designed for the new Cis
Lunar- For those who do not know: It has only 2 cells ,one is the master and has a pure O2 and a diluent (air) injector close to the cell face. Approx every minute the handset hands control over to the slave cell and test fires a small amount of O2 at the master cell and a small amount of Air, it then looks at depth and if the cell does not show correct Mv for the depth the dive is aborted, so a constant hyperbaric test while diving, VERY cool...
except.... when testing was done on various other units ,they found that when blowing on the cell face you are faced with a few issues : If there is condensation on the cell face it sometimes helps to decrease it (yay!) , OR it actually blew moisture past the membrane into the cell causing.... yes you guessed it horribly incorrect readings. And guess which one manifested itself the most ? The latter of course.

The second fun problem (had one of those) is when you get a cell stuck. That basically gets a layer of moisture onto the cell face, it traps O2 behind the water ,and the cell only sees that O2 reading ,which is usually
setpoint. Now the computer sees 1.3 1.3 1.3 while you are happily
breathing the loop down and die embarrassed...or finally, when the O2 behind the cell face gets metabolized then it will fire the solenoid... oops, hopefully you are not an idiot and do realize when your solenoid did not work for a while, or your lung volume breathes down etc... The cool thing is if it was close enough to fire the solenoid before it got stuck it might be within range to start firing and of course will not stop firing the O2 in as the cell cannot see it... he he.

So what to do.....

IMHO ,only other possibilities :Nr 1= FLUSH YOUR UNIT OR GO O/C if you think there is a problem!!!!! The ONLY reliable piece of hardware is the thing between your ears we all assume is a brain ;-) Roll cells over (BEST), if you passed a fitness test on the cells within the previous 24hrs they should be good in theory, buy a cell checker from Narked at 90 (not really worth it-can built one way cheaper- 600 Pound Sterling!) or start diving at the setpoint where calibration passed (yeah sure!) Check your cells and record linearity if possible, but as stated that will just help you to identify if a cell seems to be performing in the same fashion as the previous dive, and where to expect a slow or fast reaction. The chances of loosing 3 cells to current limitation at the same time is VERY slim indeed! But be careful of exposing and leaving the cell in excessive heat or freezing it. Use a system that independently calibrates the cells and does not "take "readings from another. Use a 4th cell if possible.

In regards to cells, AP always claimed a better and more stringent protocol when verifying their cells, seems there might be a small hiccup. AI ( Analytical Industries) makes most of the cells. I have had as many AI cells fail as PSR cells as AP cells. Once again. Roll cells over, check linearity yourself for interest. You can clearly see how an assumed linearity can produce interesting readings. Just use bit of common sense and remember :
the job of the re breather is TO KILL YOU! Your job is to make sure IT DOES NOT!
If you weren't confused before , I hope you are now ;-) Cheers for now.

Tuesday, October 14, 2008

The Argument for Rogue Agencies

The chat group has been wild over the last week or so (I did not pick up mail for 4 days and had over 80 mails sitting there). What jumped for me was a reply from one of the agencies about how they had trained all of the divers listed as ‘heroes’ in one of the responses. Now my name was on that list of heroes and I found myself with a sudden resistance to an agency laying claim to ‘glory’ just because I happen to have a certificate from them. The main argument was on creating divers with the right attitude and the agency in question was ( I guess) trying to imply that they create divers with the right attitude who become role models in the community (nothing like a blatant plug on an impartial chat site). Which just stuck in my throat. Is attitude created or is it something that was there all along ? And if it was created, by who ?
I doubt the answer is simple. Good divers start off with the ‘right’ tendencies that a ‘good’ community will re-inforce. Conversely, bad divers will be influenced by the community in which they find themselves. And there is that word again, community. The diving community is a complex animal, made up of divers, equipment suppliers, dive sites, operators and of course, the agencies. They are all interlinked, but some have more influence than others. A dive site/ operator that does not enforce standards by banning rogue divers creates an environment where there are no consequences and so allows other divers to start breaking rules. Their influence depends on the number of options out there, so dive sites have more influence than say a dive operator who has to compete with a number of similar operators and so is probably less inclined to be concerned and drive away paying customers. Then come the divers themselves, who get to choose to stand up for standards and make it known when they are broken and that it is not OK to do so. Their effect is also variable and often creates cliques of like minded divers who are hard to break into. Finally come the agencies. Now, as an agency your job is to create skilled divers. These divers become your brand, your face out in the world if you will, which implies that an agency should be carefully monitoring its divers and ensuring that they are in fact representing the right image. One would expect that agencies (both sport and technical) would pro-actively discipline its divers and instructors when they flagrantly violate the rules and standards. But they seldom do which creates an impression that (once again) this behavior is condoned. The result is that we have created a community where there are simply NO CONSEQUENCES.
So I was pleasantly surprised with ISDA. For those of you not on the chat list, this is a new, local agency that has received a lot of flak for breaking away from the older, more established agencies. It now has the unenviable title of being a rogue agency. Johan Beukes (a controversial figure in himself) decided that he was fed up with the lip service being paid to standards and to the poor quality of diver that was being created by our locally established agencies (both sport and technical), so he created his own. The recent incident where a sport instructor took open water divers on what is a full Cave, Trimix dive saw the usual blame shifting… except for ISDA, who suspended the open water diver who did the dive! In fact, they recently suspended an instructor for taking experienced open water students to a mere 40 odd meters in open water. ISDA divers know that they are their agencies brand and their agency is serious about its standards. They now know that if they break those standards there are consequences, which means that there are probably going to be a whole lot less standards being broken by those divers. Which leads me to ask the question, isn’t it time that the old, complacent agencies started to catch a wake up! Here is an agency that takes its standards and reputation seriously. Here is an agency that understands that its reputation is based on what their divers actually do AFTER the course is over!
I find myself asking the question, should I be paying more attention to ISDA and getting involved ? It would blow my neutral stand completely….but maybe it is time to stand for something, rather than against something.
We are the diving community ! Who you are and the service you demand from agencies and dive sites is what has created and what will create the community in which we dive. If you want to improve the standards out there, you need to commit to creating an expectation of action from the agencies and an expectation of compliance from the divers. And while that happens, I am going to start paying more attention to those so called rogue agencies!