FMCSA defines safety-sensitive function in 49 CFR 382.107 as all time from the time a driver begins to work or is required to be in readiness to work until the time the driver is relieved from work and all responsibility for performing work. The definition lists six categories:
1. All time at an employer or shipper plant, terminal, facility or other property, or on any public property, waiting to be dispatched, unless the employer has relieved the driver from duty
2. All time inspecting equipment as required by 49 CFR 392.7 and 392.8, or otherwise inspecting, servicing or conditioning any commercial motor vehicle
3. All time at the driving controls of a commercial motor vehicle in operation
4. All time, other than driving time, in or upon a commercial motor vehicle, except time resting in a sleeper berth
5. All time loading or unloading a vehicle, supervising or assisting with loading, attending a vehicle being loaded, remaining ready to operate the vehicle, or giving or receiving receipts for shipments
6. All time repairing, obtaining assistance for, or remaining in attendance upon a disabled vehicle
The definition matters because Part 382 ties several rules to these functions. For example, 49 CFR 382.305(m) limits random alcohol testing to times just before, during or just after safety-sensitive functions, and 49 CFR 382.601 requires the employer's policy materials to explain when in the work day a driver must comply.
Sources: 49 CFR 382.107, 49 CFR 382.305
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