All commercial trucks, truck tractor and busses must be equipped with a portable fire extinguisher. It must be readily accessible for use and securely mounted to prevent sliding, rolling or vertical movement relative to the motor vehicle.
If you are carrying hazardous materials the fire extinguisher must have a minimum rating of 10 B:C, otherwise the extinguisher must have a minimum rating of 5 B:C.
We sell two Amerex fire extinguishers that meet the 10 B:C minimum (and these are the smallest models they offer). Both come standard with a bracket designed to vehicle mounting and they meet all of the requirements set forth by the Federal Motor Carrier Safety Administration.
Model 417T is rated as a 1 A, 10 B:C extinguisher. It uses ABC dry chemical powder which while less expensive than other models, this dry chemical powder tends to adhere to hot surfaces making clean up a bit of an issue.
Model 410T is rated as a 10 B:C extinguisher. It uses a BC dry chemical powder known as Purple K. This powder is noted for being an extremely effective agent for extinguishing Class B flammable liquid and pressurized gas fires. After the fact it also provides easier clean up than the ABC powder.
Both of these fire extinguishers are dimensionally the same so the choice is in their extinguishing agent.
If you want the full Federal Motor Carrier Safety Administration regulation, click this link for Part 393.95.