Hazardous materials are products that pose a risk to health, safety, and property during transportation. The term often is shortened to HAZMAT, which you may see on road signs, or to HM in government regulations. Hazardous materials include explosives, various types of gas, solids, flammable and combustible liquid, and other materials. Because of the risk involved and the potential consequences these risks impose, all levels of government regulate the handling of hazardous materials.
(Section 9 HAZARDOUS MATERIALS - Page 9-1 para. 1 in "2005 Commercial Driver's License Manual")
Double / Triple
This endorsement allows the use of two or three trailers. There are many possible configurations of doubles and triples. This endorsement is required to operate a vehicle with more than a single trailer.
A Tank endorsement is only required if your vehicle needs a Class A or B CDL and you want to haul a liquid or liquid gas in a permanently mounted cargo tank rated at 119 gallons or more or a portable tank rated at 1,000 gallons or more.
(Section 8 TANK VEHICLES - Page 8-1 para. 1 in "2005 Commercial Driver's License Manual")
Passenger / Bus
Bus drivers must have a commercial driver license if they drive a vehicle designed to seat more than 16 or more persons, including the driver.
(Section 4 Transporing Passengers Safely - Page 4-1 para. 1 in "2005 Commercial Driver's License Manual")
If you wish to operate a school bus then you must aquire this endorsement.