There are literally dozens. Some of the more prominent ones are listed below:
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The ones I know of are PADI and Bsac. PADI is worldwide and Bsac is only in UK.
Depends on the persons certifying agency. It is different for PADI and NAUI and ...... and within each of those certifying agencies, they may have different credentials that may allow diving, but with certain limitations such as MAX depth, or has be with a certified adult etc.
The minimum age is determined by certifying agencies. The 2 most used agencies are PADI and NAUI. PADI's minimum requirement is 10, but if you are younger than 15, you will only receive a "Junior Open Water Diver." NAUI's minimum age is 12.
Not sure about travel agencies but most cruise lines and all inclusive resorts on the Ocean offer scuba excursions. Great diving in the Great Lakes too!
nothing. all agencies teach the same skills.
Certification agencies are now certifying divers as young as 10 years old with restrictions and limitations.
You don't need a licence to go scuba diving, but most people need to undergo formal training before they can scuba dive. Different agencies will take divers at different agencies, but the bigger agencies will usually not train anyone younger than 10 years old. However, some agencies insist that a student be 16 or 17 before learning to dive.
Yes, there are plenty of sites you can go to. The best one, though would be Padi. They are the best online scuba resource you can find. About.com has a good list of scuba certification agencies that you could check out.
Common Agencies: PADI IANTD NASDS TDI/SDI SSI NAUI GUE
Most scuba divers just obtain open water certifications from recreational diver training agencies, such as PADI, NAUI, BSAC or SDI.Only military or commercial divers undertake vocational diving qualifications.
Certifying Officer
most training agencies suggest that SCUBA be taught after 9years of age and should not be engaged in for one is a heavy smoker or has respiratory problems. Scuba is a high stress anaerobic activity. Anyone at risk of heart disease or arterial sclerosis should not participate. This is not medical advice. Please consult a doctor before engaging in SCUBA diving. also: if they don't want to.... too many divers start SCUBA diving to be with somebody they care for, (husband, girlfriend, etc) but have no desire to actually SCUBA dive.
A certifying official should be a supervisor in the area in which he or she performs certifications.