Too Much Oxygen can do what?

oxygenHow can the air we breathe be so harmful to us, after all isn’t oxygen good for us? Well, we do know from our Enriched Air aka Nitrox class that under pressure can become toxic to our body and cause a host of issues.

We can avoid all of those issues by paying attention to our dive computers and by setting our oxygen levels on our computers correctly. Let me provide an example that actually happen to me of all people. A day before we went to the crater I was showing a diver how to set the oxygen limits on one of my dive computers. This particular computer you can actually set up to 99% oxygen. By the way at that level the maximum dive depth is 13 feet. Well instead of making sure it was set back to regular old 21% air, I must have left it at 99%. Well you can just imagine the grief that the computer was giving me after only 5 minutes of the first dive at the crater.  As most of you know that dive is usually between 16 and 25 feet. Well after 5 minutes my computer was telling me that I was approaching my oxygen limit for 24 hours. And after 10 minutes I was way past that limit. I knew I was fine and I knew what had happened. But of course my computer didn’t know that I was fine and actually diving 21% or just regular old air.

Of course I finish both of the dives with the class and one extra for the advanced open water students. At this point I was curious what the computer would actually do. I was definitely on the naughty list as far as it was concerned.  But after 14 hours of being out of the water the computer was much happier and allowed me to reset it to 21%. After 3 more dives with the class the computer was showing only 5% of my daily oxygen exposure had been reached.

How many dives can you do in a day?

At some point during open water class a student will ask how many dives they can do in a day. The answer to that is a big “that depends”. I know that is so vague that it begs to be answered, but first let us define a dive as using a tank of air.

Digital Camera
So, just how many dives can you do in a day? Well, are they fun dives or training dives; that is taken in conjunction with a class? PADI standards say that we can do no more than 3 training dives in a day, so that answer is very clear. So how can you do your Open Water and Advanced Open Water in a long weekend or your Advanced Open Water and Rescue in a long weekend? The key word is long as in 3 day weekend. If PADI standards say we can do 3 dives in one day and we need to make 4 dives for open water and 5 for advanced open water it will take 3 days. Dive planning will be a huge part of your weekend and that is a great thing.

Can you combine training dives and fun dives in one day? Of course you can. If you finish your open water training dives in the morning and want to go out on the boat that afternoon and do a 3 tank trip, you can do that. Plan your dives accordingly with your instructor and dive buddy.  How deep are your dives going to be and how long?

So just how many dives can you do in one day? Again, that depends on you and your buddy and how you plan your day and what gas is in your tank. On the liveaboards, we generally do 4 to 5 a day. The dives are generally about 80 feet and for close to an hour with at least 90 minutes or so between dives and yes we are diving computers and nitrox. But, if we are going to explore a shallow reef at so 40 feet on regular air with 90 minute surface time we can probably make 5 or 6. Change air to nitrox and you can cut your surface time to 60 minutes and easily make 6 maybe 7.

So how many dives can you do in one day? That depends on you and your dive planning skills.


Do you keep a log book?

log book coverThe other night I did a pool refresher for a family that had just finished their pool class with an independent instructor. I asked to see their log books and was told that they didn’t get one in their class. Your log book is one of your most important tools as a diver. Not only is it a required item in your PADI Open Water class (page 39 of the PADI instructor manual), but it is a place where you can record all of your training and all of the fun adventures that you share with your dive buddies.

Your dive log as I tell all of my new open water divers is your personal journal. You can write as little or as much as you want.  There are all sorts of dive logs out there and yes there are many apps that will log your dive.  You can download your computer and just print it off or you can take a note book and make you own personal version of a dive log.  The choice is yours.

log book pageLet us take a look at the basic dive log page.  The most common of dive log pages has a place for the name of the site, the day you dove and what number is this dive for you.  The other common features of a dive log page is a place to record the air and water temp, what exposure suit if any and a very important bit of information, how much weight did you use.  Along with depth and time and air consumption, how much weight we use is very important so the next time we go diving we can be weighted correctly to start with instead of guessing.

But Scuba Joe, I don’t want to write a novel in my log book.  As I said, you can write what you want, but I do like to note the new creatures I saw and maybe anything interesting that happened on the dive such as someone reaching a milestone dive of 50 or 200.

In preparing for our upcoming adventure to the Turks, I was curious what the water temp might be and the Explorer people are reporting 80 degrees.  Nice 3 mil wetsuit, but then I thought since I dove there in 2007 and I remember it was chillier than that we pulled our log book since we are going about the same time of the year ( actually 2 weeks later)  and sure enough water temp was recorded from 73 to 78.  Sounds like my 5 mil semi-dry.

Yes, we log our dives and it saved me from being cold on our next adventure.scuba joe

Translating water temp

PADI LogoStudent: If the water temp of the pool is 81 degrees why do I need a wetsuit?

Instructor: Well, if you remember from your reading and class that water takes heat from the body 20 to 25 times faster than air.

Student: Do I need to use the wetsuit?

Instructor: It is your choice, everyone is different; but why don’t I bring it to the pool just in case.

As instructors and dive shop people, we get asked all the time about what type of wetsuit for different wonderful islands that people are traveling to and fortunately we have been in a lot of different water temp and can usually help out in trying to get a suit that will work for most people. Everyone is different, on one trip to Hawaii I was diving in my 3 mil with a hooded vest and still felt a little chill. Some friends where in their 7 mil suits with hood and vest and Donna was in her 5 mil and hood and vest, then there were the young guys from San Diego that were diving in skins or just their board shorts.

Let’s take a look at water temp as it relates to air temp. As we know water will take the heat from your body 20 to 25 times faster than air.

80 degree water = 68 degree air

75 degree water = 50 degree air

70 degree water = 32 degree air

On a nice late spring day with the air temp at 80 degrees we are all probably running around in shorts and light shirts and enjoying the sun. 80 degrees is a nice day to hang out at the pool or beach.  But 68? I might be playing golf in shorts, but I will have a light weight pullover to keep me warm. 75 degree days? No worry, it is nice and beautiful, but 50 degrees is chilly and I am wearing a coat.

Instructor to Student: You cold?

Student: (shivering) not to bad

Instructor:  You are turning blue, please go put the wetsuit on

Student: Ok, I am a little cold

Instructor: (smiling)ok


      As always happy bubbles and feel free to leave a comment