Technical Diving International (TDI) claims to be the largest technical diving certification agency in the world, and one of the first agencies to offer mixed gas and rebreather training. TDI specializes in more advanced Scuba diving techniques, particularly diving with rebreathers and use of breathing gases such as trimix and heliox. TDI trained divers have explored wrecks that are usually considered beyond the recreational range, such as the Andrea Doria as well as cave diving in Spain, Australia, Florida, Czech Republic and Mexico and assisting as support divers on world record freedives done in the Red Sea.