Under 49 CFR Part 382.107, a safety-sensitive function includes all time from the moment a driver begins work or is required to be in readiness to work until the time they are relieved from work. This encompasses: driving a CMV, inspecting or servicing the vehicle, being in attendance on the vehicle, loading or unloading, performing repairs, waiting at a facility, and all time spent at a carrier or shipper plant. Employees in safety-sensitive functions must be tested under DOT drug and alcohol testing programs and are prohibited from using alcohol within 4 hours of performing safety-sensitive duties or reporting for duty with an alcohol concentration of 0.04 or greater.