Scuba Chip once bubbled...
Solo Diving isn't any riskier than buddy diving....... unless you're a relatively new diver, in which case, you need a knowledgeable dive buddy to show You the way.
TDI now offers a course, and grants certifications in Solo Diving.
TDI DOESN'T offer a solo rating SDI does.. the solo program is not a technical rating rather a recreational rating.. TDI and SDI are treated as seperate entities under the same corporate umbrella.
ANDI also have a solo diver rating, its a tech rating and one of the prerequisites is already being a certified technical diver.