Wrong gases?

[DandyDon]

DD, he probably expected 55ppm of CO because that is the pollution we have over here from our cars and the factories in nearby Indonesia. I am only partially kidding but I bet he was mis-quoted too.

Intake air may well be tainted in the area of 10ppm or worse, all the more reason to have filters and scrubbers. Do you know what the norm is there for compressors?

I don't guess you have a personal CO analyzer?

 

[Zippsy]

Ayisha, I don't iunderstand open verdict here either. It someone were to be shot in the back of the head while hog-tied, they would likely call it an open verdict here.

DD, Sorry, I don't know much about the compressor standards here. I've seen your comments on testers but I don't have one. I actually do smell and taste my air and I teach it too.

 

[DandyDon]

Ayisha, I don't iunderstand open verdict here either. It someone were to be shot in the back of the head while hog-tied, they would likely call it an open verdict here.

DD, Sorry, I don't know much about the compressor standards here. I've seen your comments on testers but I don't have one. I actually do smell and taste my air and I teach it too.

You understand that gives you virtually no warning on CO content? The H2S in that tank should have smelled like rotten eggs, but the CO in that tank even at that alarming level is without color, odor, taste, etc? The only way to know is to test; if over 10 ppm - reject.

Are you an Inst? If so, you can get a Scubaboard badge you know? Nothing personal, but if Insts don't know about compressors nor test for CO as many seem to not, the current risk level is only going to get worse if any change at all as safe air cost a little more to produce than commonly accepted air, yet CO cases are usually missed - dismissed as "travelers flu" and "motion sickness" among those who get ill but survive, drownings for those who die without toxic studies of tank and corpse, or simply not reported to the public if found.

 

[swamp diver]

I'm bothered by this excerpt from the latest version: "Another tank taken off the boat was found filled with the expected 20.7 per cent of oxygen, 55 ppm of carbon monoxide and 1.7 ppm of hydrogen sulphide."

Wrong Wrong Wrong! The common scuba industry maximum is 10 ppm CO, and expected should be less than 1 ppm. Can't do anything about journalism but I thot the facts may be interesting here.

The Associate Professor Philip Eng of the Department of Respiratory Medicine was probly being quoted out of context.

I have no idea what the maximum allowed or average expected of H2S2 might be?

The Immediately Dangerous to Life or Health (IDLH) for carbon monoxide is 1200 ppm and at 1.8 ATA Mr. Sue would have had a surface effective concentration of 1413 ppm. In other words he likely would have drowned solely on the basis of the CO exposure alone without the additional hydrogen sulfide (H2S).

"The current NIOSH definition for an immediately dangerous to life or health condition, as given in the NIOSH Respirator Decision Logic [NIOSH 1987], is a situation "that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment."
NIOSH: Documentation for Immediately Dangerous to Life or Health Concentrations (IDLH) / NIOSH Chemical Listing and Documentation of Revised IDLH Values (as of 3/1/95) - intridl4

H2S normally in atmospheric air is measured in parts per billion (ppb) typically < 1 ppb unless near pulp plants, manure piles, sewage treament plants, etc.. Assuming the parts per million (ppm) reference in the newspaper article is correct an exposure of 12.3 ppm at 1.8 ATA is equivalent to 22 ppm at surface which is well above what would be recommended for air diving. The current ACGIH threshold limit value (TLV) for H2S is 1 ppm for an 8 hour exposure. Looking at the British equivalent EH40 table their 8 hour maximum exposure level is 5 ppm. Normally to determine the maximum contaminant exposure level for air diving one calculates 1/10 the TLV for the contaminant in question. For H2S therefore the maximum concentration in the compressed air for diving should have been from 0.1 ppm to 0.5 ppm.

There is no question in my mind that this gentleman died from his CO/H2S contamination in his tank air. The question though is by what mechanism did the contaminants end up in the breathing air?

One mechanism would be the same as the Baani Explorer Maldivian CO incident in that the internal combustion engine's exhaust was entrained into the compressor's intake. I do not know the average concentration of H2S in the exhaust from an engine without a catalytic converter?

The second possibility is that the compressor was poorly installed and the compressor oil auto-ignited or "dieseled" in the overheated stage leading to CO and H2S production. Typically this happens with a low flash point mineral oil where the additive package often has sulfur-based products which under thermal breakdown will produce hydrogen sulfide and sulfur oxides. This is documented in the attached MSDS (section 3 and 10) for a Shell mineral oil commonly used in breathing air compressors and in fact was loaded into compressors at one manufacturer until quite recently.

As the Maldivian CO poisoning incident revealed many of the divers did not show a drop in their level of consciousness until surfacing when the additional oxygen dissolved in the plasma was reduced on ascent. I suspect though at the extremely high levels of CO this very unfortunate diver was exposed to even the additional O2 dissolved in the plasma at depth was inadequate to compensate for the direct tissue (brain, heart, skeletal muscle) toxic effects of the CO and H2S.

The only thing which may have saved this diver given his short exposure time was if another diver had been able to inflate his BCD, apply 100 percent oxygen, and get him to a hyperbaric chamber for treatment of his CO poisoning in order to prevent many of the longer term sequelae seen in acute CO poisoning incidents with loss of consciousness.

While the CO would not have been detected by smelling the tank air prior to diving as it is odourless, the H2S clearly would have been very evident by the rotten egg smell. Unfortunately the activated charcoal in the purifier will not remove H2S and unless the operator was running a cartridge with catalyst the CO would have passed directly into the fill as well. As we saw in the Maldivian CO incident the compressor operator did not install the filter with catalyst which should be used whenever an IC engine is used to power a compressor. One wonders if this was the case in this incident?

 

[wilde100]

DD, he probably expected 55ppm of CO because that is the pollution we have over here from our cars and the factories in nearby Indonesia. I am only partially kidding but I bet he was mis-quoted too.

Wilde, I was taught OW and Rescue at Hantu and I did my IDC there. What should have the instructor done? I'll get hit for saying this but 1) not dive there while currents are strong (which means checking tide charts and/or moving the boat; 2) kept closer watch over the students (DM's in the water); 3) train them better in the pool (more than one 3 hour class); and 4) don't overweight the student.

When I did my OW there, two minutes into my first dive, my buddy's waving arms knocked off my mask and reg. Because of the excellent training I got (including 4 pool sessions rather than the one that this guy almost certainly got), I calmly found both and replaced them in time to see the passing turtle. Competition in Singapore for students has meant that the course cost has come down steadily over the years just as the cost of living has gone up considerably. What do you think gets cut? Sad, ain't it.

Thanks Zippy. Alot of your suggestions address the pre-incident details.
I'm just curious whether the instructor was also on surface actively looking for his missing student or did he inform his colleague and go back down to take care of his other student.

I'm pre-disposed to option 1, for the instructor to have thumbed the dived and look for the student.

 

[Zippsy]

According to an eyewitness on the boat, the instructor "told the divers to return to the boat and then asked for a back-up boat to join them at the scene". That's all I can find on the subject and it does not really give the exact sequence about when the instructor searched on the bottom, notified the DM in the boat and sent / brought up the other student.

 

[NudeDiver]

"The tank, which should have contained 80 per cent oxygen and 90 per cent nitrogen". I'm not even going to comment on that absurd statement...

Maybe it's a particularly large tank.