Diving the wrecks of Coron Bay

For the last three days we've been diving the wrecks of Coron. Located just to the north of Palawan, on the island of Busuanga it is one of the most spectacular wreck diving sites. Amongst the scenic bays and narrow passages between islets surrounding Busuanga lie Japanese navy's auxiliary transport vessels. They were sunk during two air strikes on September 24th and October 9th 1944.

Altogether there are 7 wrecks around Busuanga, but we dove only 6 of them:

• Okikawa Maru
• Akitsushima
• Taiei Maru
• Olympia Maru
• Tangat Wreck
• Irako

More on history of Coron wrecks.

All the diving was done from the spiderlike bancas, traditional filipino boats now used for everything from transport to fishing to diving. The wrecks are rather deep for recreatioal diving, ranging from 25 to 45 meters, and all the dives we did were penetration dives. It is very easy to exceed your No Decompression Limits under such circumstances, especially if the divemaster minds only his computer which is less conservative than yours. After spending 17 minutes on decompression stop on the first days second dive we decided to use nitrox for second dives on the last two days.

The wrecks were just amazing, especially the auxiliary oiler Okikawa Maru. With her spacious tanks. Although the visibility outside was just 10 meters, inside the wrecks the water was much clearer (until someone made a false move and stirred up the silt...).



All of the dives were penetretion dives, though for less experienced divers it is also possible to stay outside the wrecks and still have a lovely dive. We were ofcourse led by a divemaster, otherwise we would have probably gotten lost and I wouldn't be writnig this. Inside the wrecks are rather comfortable, though we had to watch our heads most of the time and there were a few tight squeezes - we once exited a wreck through a propeller shaft.

PADI online course evaluation

Today I got an email from PADI asking to fill in an online course evaluation questionnaire about my nitrox course. This seems to be a big step forward for their QA - online questionnaire is more likely to get filled then the printed one and because of that they'll more information on who is training according to what standards. So far I received 2 or 3 printed forms and haven't sent back any...

The questionnaire itself was a bit buggy. For example there where many questions about dives conducted during training, but the new standard for PADI Nitrox training doesn't require any dives...

On Nitrox

So, now that I've become a nitrox diver I can reveal some secret nitrox knowledge:). Below goes an executive summary of nitrox diving. You can find a more detailed description on Wiki (wiki EAN).

Nitrox is a mix of nitrogen and oxygen. Usually nitrox contains more oxygen than air (>21%) and in such case it's called Enriched Air Nitrox or EAN. Some call any mixture of these two gases nitrox. For recreational diving a blend of up to 40% of oxygen is used, however technical divers use hotter (containig >40% oxygen) nitroxes to accelerate decompression. The two most popular mixes are EANx32 and EANx36 containing respectively 32% and 36% of oxygen.

Nitrox diving has become popular because because of the advantages this breathing mix offers. The main advantage is that because of lower nitrogen level divers body absorbs less nitrogen and thus the No Decompression Limits (NDLs) are longer. That means one can spend more time underwater or increase the seafty margin by using nitrox and staying withing air NDLs. Some people also report feeling less tired after a nitrox dive compared to an air dive. Previously people thought that breathing nitrox reduces effects of nitrogen narosis, however this turned out to be untrue because oxygen's narcotic potential is even higher:)

There are some dangers when it comes to diving with EAN and these are: oxygen toxicity and risk of fire/explosion. Both of these come from the increased level of oxygen in the mix and are easily avoided.

Fire may be caused when oxygen rich breathing mix comes into contact with materials that are not oxygen compatible or not oxygen clean, meaning that they simply start to burn in contact with such mix. To avoid this simply use oxygen clean and compatible equipment when diving with nitrox.

There are two types of oxygen toxicity: central nervous system oxygen toxicity (CNS) and pulmonary oxygen toxicity. The cause of CNS is still unknown, it is observed when the partial pressure of oxygen in the breathing mix is above 1.4 ata. CNS may result in convulsions (the most severe case), which may be lethal to a diver. Pulmonary oxygen toxicity is caused by prolonged exposure to higher than normal oxygen levels and results in lung inflamantion, coughing and decreased lung volume. These symptoms usually recede. To avoid oxygen toxicity you must monitor your oxygen exposure and maximum operating depth (MOD). MOD is the depth at which oxygen partial pressure reaches the maximum safe level (1.4 ata). Modern diving computers can usually track both of these parameters and alert the diver when he is reaching the limits. This feature does not mean you don't have to plan your dive.

Diving cylinders used with nitrox should be specially marked and have the MOD for the mix that they contain written on them. To mark cylinders usually a sticker is used, just like the one below:

EAN can be obtained by different methods. Generally you can add some oxygen to air or remove some nitrogen from it. Adding oxygen is done in partial pressure mixing or continuous blending mixing and oxygen removal is performed by using a special membrane in gas separation mixing
Wikipedia has a fairly good article on gas blending

EAN Done :)

Passed the exam, which was fairly easy. In fact all the PADI certification exams I passed so far were not too hard. I mean, of course the theoretical part, because the Rescue Diver diving part was a killer. Especially the 'climb the ladder with your buddy sitting on your knee' part. We almost failed that...
Anyways, we are now certified EAN divers, which isn't a big progress towards becoming a DM, but during the course we got to talk to some divemasters at our center. That gave us some insight into prospects of divemastering here, in Poland, and they weren't very bright, though they weren't very pessimistic either.
And apart from all of the above the first step towards tec diving has also been made:D

Rich Air

Funny little specialty. No dives necessary, just theory, about 6 hours. The Enriched Air Diving coursebook has only 100 pages, most of which are pictures (as usual). So today we've learned about Equivalent Air Depth, CNS, POT and some other things. Got some new tables, though they are almost the same as standard RDP. Next class is going to be more fun as we are going to use oxygen analyzers and, of course, write the exam.