Technical divers can search for Robredo
MANILA, Philippines – The divers searching for the missing aircraft of Interior and Local Government Secretary Jesse Robredo off the coast of Masbate need special equipment and training to venture deeper than 40 meters under the sea.
Transportation Secretary Manuel "Mar" Roxas III tweeted on Sunday, August 19, that the search areas have depths between 40m and 87m.
He also claimed that scuba divers can only stay at that depth for up to 10 minutes to avoid nitrogen narcosis, a condition which has an effect similar to being drunk. Nitrogen narcosis happens when there is too much nitrogen in the bloodstream, affecting the consciousness and impairing the judgment of an individual.
Search area has depths of 40 to 87 mtrs. Human Scuba can only do 10 min at 40 mtrs before nitro narcosis.— Mar Roxas (@MARoxas) August 19, 2012
This is true for diving with regular air, but divers can actually stay much longer – up to about 30 minutes at 87m – if they are trained for technical or mixed-gas diving.
Longer decompression time
One of particularities of technical diving is the longer decompression time – number of minutes they must wait at certain depths to avoid experiencing decompression sickness or "the bends" – compared to diving with regular air.
That makes technical dives sometimes last more than two hours, compared with between 45 minutes and one hour for a normal air dive.
Whereas recreational scuba diving is with 21% oxygen compressed air, technical diving uses mixes normally involving helium in order to prevent oxygen toxicity when you go deeper than 55m.
The first sign of oxygen toxicity is usually a convulsion without warning which usually results in death, as the breathing regulator falls out and the victim drowns. Sometimes the diver experiences nitrogen narcosis as a warning signal.
By adding helium to the breathing mix, the percentage of oxygen is reduced and once it is below 18% it is safe for deep diving.
Technical divers normally carry at least 3 tanks and a device called a rebreather.
A rebreather is a closed-circuit breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantially-unused oxygen content of each breath. Fresh oxygen is added to replenish the amount metabolized by the user.
According to PADI, the world's largest recreational diving membership and diver training organization, technical diving is "diving other than conventional commercial or recreational diving that takes divers beyond recreational diving limits."
"It is further defined as an activity that includes one or more of the following: diving beyond 40 meters/130 feet, required stage decompression, diving in an overhead environment beyond 130 linear feet from the surface, accelerated stage decompression and/or the use of multiple gas mixtures in a single dive."
A wide range of operators offer technical diving certification in the Philippines, where there are many deep shipwrecks ideal for this special type of diving. – Rappler.com
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