Unknown Tourist dead, Dive Master ill - Ambergris Caye, Belize

[stiebs]

I'm assuming that where the lady says "atrial" bleeding she means "arterial" bleeding?

Her account shows that she has a level of medical knowledge beyond the layperson (including me), and no doubt knows the difference between atrial and arterial.
Arterial refers to arteries (ie, the blood vessels leaving the heart)
Atrial refers to the hearts upper chambers of the heart.

 

[Dan G]

This is from the Undercurrent article quoted a few pages ago, and I would like to know why this is true:

It's more likely that the nitrox mix is suspect. This can happen especially if the nitrox is made
by partial pressure blending (when neat 02 is added to a tank and then
topped up with air) rather than de-nitrogenizing air through a membrane system.

Does gas mixing this way throw off the analyzer?

 

[LI-er]

A quick search brings up a related ScubaBoard thread

Anyone ever hear of tank rolling after mixed gas fill??

Ok - I'm going to come out and admit it - I've never seen this before..... ever. UNTIL we got our tanks filled at a PADI dive center down in West Palm Beach somewhere. For those of you who don't know what I mean - after a NITROX fill, the lady who filled the tank proceeded to lay the tank...

scubaboard.com

that has the following posts:

Note: At times, it may be necessary to roll the tank on the floor, before measuring, to get a correct reading. In particular, Nitrox made by the blending process is sometimes stratified after the air is added to the Oxygen. This results in a low Oxygen reading. After a few hours, mixing takes place by itself. However, if in doubt, or to speed things up, roll the tank on the floor for 5 to 10 seconds. Once mixed, Nitrox stays mixed.

Most nitrox tanks are filled by partial pressure blending, meaning that oxygen is placed in the cylinder and then diluted with air. When analyzing nitrox mixes more than 50 percent it's important to remember that a properly filled tank will allow the gas to form layers. Oxygen is heavier than nitrogen and, because it is put into the tank first, it may lie on the bottom, giving an artificially low reading on initial analysis.

 

[TrimixToo]

This is from the Undercurrent article quoted a few pages ago, and I would like to know why this is true:

It's more likely that the nitrox mix is suspect. This can happen especially if the nitrox is made
by partial pressure blending (when neat 02 is added to a tank and then
topped up with air) rather than de-nitrogenizing air through a membrane system.

Does gas mixing this way throw off the analyzer?

Without context I'm not sure what the author is getting at. However, it takes time for partial pressure blends to mix if the gases are added slowly (as they should be). If the tank is analyzed immediately after a PP blend started with O2 and finished with air the analyzer will often read a lower percentage of O2 than the mix will actually contain afterward. Many people (including me) roll tanks for a minute or so before analyzing. The blender should know what the original analysis was if the tank wasn't empty and know within a percent or so what the final mix should be. If the analysis isn't really close to that, either the blender made a mistake or the gases are still mixing.

This is one reason you must always analyze your gas personally. Most often, you won't do that immediately after the blender has finished, which gives the gases time to mix completely.

I'll add that membrane systems have the same problem unless the tank is completely empty to start with, though the difference between the existing content and the final mix is often smaller.

There have been any number of discussions in the past about whether the mix should "instantly" be complete or whether it takes time. Certainly the time is nonzero, so the real question is "how much time"? I dunno. At least a few minutes, perhaps a few hours if the tank doesn't get moved around much, I mix, roll, analyze, and then analyze again pre-dive. As long as the two analyses agree I'm happy.

Does this help?

 

[Seadogcentre]

I just registered my shop on scubaboard and then come across this article about Belize. All I can say is the shop I'm getting ready to open will always be safety first. Air quality tests every 6 months. Tanks cleaned annually on the inside. Compressor has a CO monitor attached to it.

 

[DandyDon]

I just registered my shop on scubaboard

Welcome to the discussions.

Air quality tests every 6 months.

I never thought much of those as compressors can vary so much and the six-month samples can be taken on a slow day on a new filter and all.

Compressor has a CO monitor attached to it.

Now that works, if you have automatic cutoff enabled.

 

[Seadogcentre]

Welcome to the discussions.

I never thought much of those as compressors can vary so much and the six-month samples can be taken on a slow day on a new filter and all.

Now that works, if you have automatic cutoff enabled.

I haven't had much problems with mine. It only has 1400 hrs on it. Plus I had 4th stage replaced before bringing it down here.

 

[Dan G]

Without context I'm not sure what the author is getting at. However, it takes time for partial pressure blends to mix if the gases are added slowly (as they should be). If the tank is analyzed immediately after a PP blend stated with O2 and finished with air the analyzer will often read a lower percentage of O2 than the mix will actually contain afterward. Many people (including me) roll tanks for a minute or so before analyzing. The blender should know what the original analysis was if the tank wasn't empty and know within a percent or so what the final mix should be. If the analysis isn't really close to that, either the blender made a mistake or the gases are still mixing.

This is one reason you must always analyze your gas personally. Most often, you won't do that immediately after the blender has finished, which gives the gases time to mix completely.

I'll add that membrane systems have the same problem unless the tank is completely empty to start with, though the difference between the existing content and the final mix is often smaller.

There have been any number of discussions in the past about whether the mix should "instantly" be complete or whether it takes time. Certainly the time is nonzero, so the real question is "how much time"? I dunno. At least a few minutes, perhaps a few hours if the tank doesn't get moved around much, I mix, roll, analyze, and then analyze again pre-dive. As long as the two analyses agree I'm happy.

Does this help?

I understand what you are saying, think analyzing pre-dive makes a lot of sense, yet based on much of the thread linked above about "tank rolling," there is much disagreement. Also, as recreational divers the Belize divers were likely not using a mix above 40%, much less 50% which is where the layering issues are mentioned to be a factor. I wonder if tank cooling is a factor greater than the actual mixing of gasses, especially with O2 and N2 which are almost identical in weight.

 

[TrimixToo]

I just registered my shop on scubaboard and then come across this article about Belize. All I can say is the shop I'm getting ready to open will always be safety first. Air quality tests every 6 months. Tanks cleaned annually on the inside. Compressor has a CO monitor attached to it.

Respectfully, every 3 months on the old filters would be much better than twice a year. Monthly, even, if you're pumping a lot of gas. I applaud the use of an attached CO monitor.

 

[TrimixToo]

I understand what you are saying, think analyzing pre-dive makes a lot of sense, yet based on much of the thread linked above about "tank rolling," there is much disagreement. Also, as recreational divers the Belize divers were likely not using a mix above 40%, much less 50% which is where the layering issues are mentioned to be a factor. I wonder if tank cooling is a factor greater than the actual mixing of gasses, especially with O2 and N2 which are almost identical in weight.

Time, as I said, also works. So does transport by car or truck. But the essential point is that you do what you have to do to figure out what's happening when the mix is not what's expected. The analysis should closely match the intended blend. When it doesn't, you can wait, you can roll, you can put them in your car and test at the dive site, you can dump the tank and start over (perish the thought!) probably with the same result, whatever. Rolling is fast (shrug). I've been a certified gas blender for over a decade for both nitrox and trimix. What works for me works for me. When you start blending for yourself, you can find what works for you. This is one area in which I really don't care what others think unless they are more experienced, and even then I'll take it under advisement. They're not using my equipment to do their blends.