Although Nitrox has been used for recreational diving for almost 25 years, it is still often misunderstood.
As an instructor, I have found myself correcting countless students and divers who are under the impression that Enriched Air Nitrox (EANx) diving enables a diver to dive deeper than with normal air. This is a common misconception about nitrox diving.
I hope that this blog will help to make sense of what it is and what it can do for you, but remember you do need specific training before diving using Enriched Air for the first time.
What is Enriched Air diving?
Already the words Nitrox and Enriched Air have been interchanged in this blog entry. That is because Nitrox quite literally refers to a mix of nitrogen and oxygen, regardless of the percentage of each in the mix, which could be means air could be called nitrox (21% Oxygen, 79% Nitrogen).
We should properly call the nitrox we use while diving “enriched air nitrox". It refers to any blend of nitrogen and oxygen in which the oxygen concentration is greater than that of normal air. This means an oxygen level of 22 percent or higher, although the most common enriched-air nitrox blend is 32 percent. The recreational diving limit is 40 percent oxygen.
What does it do?
As every entry level diver knows, increased pressure at depth causes our bodies to dissolve the nitrogen in the air we breathe into our bloodstream. This nitrogen absorption limits the time that we can spend underwater. As we dive deeper and for longer, we absorb more nitrogen at a greater rate. Our no decompression limit correlates to the amount of nitrogen our bodies can absorb before we must perform compulsory decompression stops or suffer the consequences of decompression sickness.
Enriched air nitrox slows down the nitrogen dissolution rate in our bloodstream, because there is less nitrogen in the mix that we’re breathing. The higher the percentage of your enriched air blend, the more extra oxygen will replace nitrogen.
Benefits of Enriched Air Nitrox Diving(EAN)
Divers use enriched air nitrox for several reasons. An increased no decompression limit means longer bottom times. The lower percentage of nitrogen in the nitrox you’re breathing means your bloodstream is also absorbing nitrogen more slowly.
EAN is best applied to shallower dives. As an example of the improved bottom time one may realise by using EAN is for a diver making a dive to 18 metres on air has a no decompression limit of 56 minutes. In contrast, a diver making the same dive on Nitrox containing 36% oxygen would have a no decompression limit of 125 minutes. That's an hour more bottom time! (Results based on the PADI Recreational Dive Planner)
Surface intervals are usually shorter on nitrox as well. Since there is less nitrogen to off-gas, a diver on enriched air will be able to re-enter the water sooner than a diver using normal air after completing the same profile. This also means that divers using enriched air typically have longer maximum bottom times on repetitive dives.
Enriched air divers are often less tired at the end of the day as well because of less off-gassing.
Enriched air can be a valuable safety buffer for divers who choose to use it while following normal air tables, computers, profiles and procedures. Doing so creates a considerable conservative margin that further reduces the risk of decompression sickness.
Anyone who may be susceptible to DCS, such as those who are tired, overweight, older, have suffered decompression sickness before, or are diving with injuries, should consider diving Enriched air
Myths, considerations and dangers
Although the benefits of diving with enriched air are significant, doing so also involves certain risks. One of the most common misconceptions about enriched air nitrox is that users can dive deeper than with normal air; in fact the opposite is true.
Under pressure, oxygen becomes toxic. The percentage of oxygen in normal air (21 percent) only becomes toxic at depths greater than the recreational limit. But the increased percentages of oxygen in enriched air mean that toxicity can become a problem at much shallower depths.
Toxicity causes convulsions that put a diver at risk of losing his regulator and subsequently drowning. However, enriched air courses teach divers how to work out their maximum operating depth using the percentage and partial pressure of the oxygen in their mix.
As long as you adhere to the maximum operating depth, oxygen toxicity should not be a problem.
Although it is safe to use standard scuba equipment with air blends containing up to 40 percent oxygen, the process by which an enriched air cylinder is filled often involves much higher concentrations.
Partial pressure blending exposes the cylinder to pure oxygen that techs later dilute with normal air. If they are not treated for exposure to such high levels of oxygen, cylinders can explode. Therefore, any part of the cylinder that comes in to contact with pure oxygen needs to be “oxygen clean.” You cannot interchange cylinders used for enriched air and normal air. Enriched air cylinders require decals or stickers to differentiate them from normal ones; service them annually.
There are a few other equipment considerations to bear in mind when thinking about enriched air diving. Before each dive, you are personally responsible for checking the percentage of oxygen in your cylinder. If it is even slightly off, your maximum operating depth (MOD) calculations will be too. You will need an analyser to check. Although you can usually borrow one from your dive center, it’s a good idea to have your own if you intend to dive nitrox regularly.
If you dive with a computer, you need to make sure that yours has enriched air settings. It must correlate to the details of your mix before beginning each dive. Remember that enriched air does not improve air consumption, and neither does it give immunity to decompression sickness.
Continue to check your gauges, depth and time limits as often as you would when diving on normal air.
With these precautions and the necessary training, nitrox diving is a fantastic way to get the most out of your diving experience. You’ll spend more time in the water, and less time waiting to get back in.
Should I do the Enriched Air Speciality?
On the 15th of January 2018 NHS England launched a 30 day public consultation for the Reviewing of Hyperbaric Oxygen Services in the UK.
This consultation will close on 14th of February so there is not much time to contribute your views.
One of the points of discussion is a proposal to reduce the number of UK chambers from the current 10 to a MAXIMUM of 8. Obviously a maximum of 8 could end up being LESS THAN 8.
We all hope we never need to use the services of a recompression chamber but if we do, we don’t want a long journey before treatment can start. Reducing the number of chambers would have an effect on the efficacy of treatment as the speed of the initial treatment starting is imperative to its success. This could make symptoms worse, increase total treatment costs and reduce the chances of making a full recovery.
On Tuesday this week at the British Diving Safety Group this issue was raised and now the agencies are raising the awareness and asking for your support by sending this link out. Please share this post so we can spread the word to as many people as possible. There’s a link to the relevant survey - we need to make sure that the views of divers are received.
A response from the British Diving Safety Group is being produced, but it is essential that individual divers also respond.
Please complete this survey and spread this important message to all UK divers.
The PADI Rescue Diver course is known for being a demanding course — both physically and mentally — but it’s also praised for giving you the training that will boost your confidence and hone your diving skills more than any other course.
Take this course, and you’ll dive more confidently knowing that you’ve expanded your emergency prevention and management skills
When can you do this? Well our next Rescue Course dates are as follows:
14th April with follow on sessions on 21st April / 28th April / 5th May / 12th May; and
Open Water Sunday 20th May
Contact us to discuss and / or book your space.
First Aid qualification not within the last two years, no worries we have a course running on Saturday 20th January.
How much blood do we have?
The amount of blood in our body varies in relation to our size. A rough rule is that we have approximately one pint of blood per stone in body weight (0.5 litres per 7kg), so the average adult has between 8 and 12 pints (4.5 to 6.5 litres) of blood, dependent on their size and can safely donate 470ml (just under a pint) during a blood donation. However, rapid blood loss of 2 pints or more can lead to shock and death
Remember that children have less blood than adults, and as such cannot afford to lose the same amount.
External bleeding refers to blood coming from an open wound. The term haemorrhage refers to a large amount of bleeding in a short period of time. External bleeding can be classified into three types according to the type of blood vessel that is damaged - artery , vein or capillary.
Blood in the arteries is under direct pressure from the heart pumping and spurts in time with the heartbeat. A wound to a major artery could result in blood ‘spurting’ several meters and the blood volume will rapidly reduce. Blood in the arteries is rich in oxygen and is said to be bright red’, however, this can be difficult to assess.
This is the most serious type of bleeding because a large amount of blood can be lost in a very short period of time. Arterial bleeding also is less likely to clot because blood can clot only when it is flowing slowly or not at all. However, unless a very large artery has been cut, it is unlikely that a person will bleed to death before the flow can be controlled. Nevertheless, arterial bleeding is dangerous and must be controlled.
Veins are not under direct pressure from the heart, but veins carry the same volume of blood as the arteries.
Blood from a vein flows steadily or gushes. Venous bleeding is easier to control than arterial bleeding. Most veins collapse when cut. Bleeding from deep veins, however, can be as massive and as hard to control as arterial bleeding.
This is the most common type of bleeding as it bleeding from capillaries occurs in all wounds. Although the flow may appear fast at first, blood loss is usually slight, usually not serious and can be easily controlled. Bleeding from a capillary could be described as a ‘trickle’ of blood.
Quite often, this type of bleeding will clot and stop by itself.
Each type of blood vessel—artery, vein, or capillary—contains blood of a different shade of red. An inexperienced person may have difficulty detecting the difference but identifying the type of bleeding by its color is not important.
Life threatening bleeding is a medical emergency. First aiders should be competent at dealing with major blood loss but the key first aid treatment for all of these types of bleeding is direct pressure over the wound.
We regularly run Emergency First Response - Primary Care (CPR) and Secondary Care (First Aid) combined courses. During the Secondary Care section of this course how to recognise and handle bleeding is covered. Our next course is on Saturday 20th January so come and join us.
Congratulations to all of our students who achieved certifications during December and one who was missed from our November congratulations.
Paul B O'Rourke
Paul R O'Rourke
PADI Open Water Instructors, who I know we have already congratulated but always deserves another mention
Curiosity and a thirst for adventure is why many of us become divers in the first place. But we aren’t going to take the plunge with just anyone so why should new divers.
So to all those potential new divers or even those qualified who are looking around at courses and Dive Centres have a look at our article How to Choose a Dive Centre. Then pop in have a chat, maybe a cup of tea or coffee and if you like what you see, learn to dive with us here at Dive Rutland or join our club everyone is welcome.