49 CFR § 397.5 - Attendance and surveillance of motor vehicles.
(a) Except as provided in paragraph (b) of this section, a motor vehicle which contains a Division 1.1, 1.2, or 1.3 (explosive) material must be attended at all times by its driver or a qualified representative of the motor carrier that operates it.
(1) The vehicle is located on the property of a motor carrier, on the property of a shipper or consignee of the explosives, in a safe haven, or, in the case of a vehicle containing 50 pounds or less of a Division 1.1, 1.2, or 1.3 material, on a construction or survey site; and
(2) The lawful bailee of the explosives is aware of the nature of the explosives the vehicle contains and has been instructed in the procedures which must be followed in emergencies; and
(3) The vehicle is within the bailee's unobstructed field of view or is located in a safe haven.
(c) A motor vehicle which contains hazardous materials other than Division 1.1, 1.2, or 1.3, materials, and which is located on a public street or highway, or the shoulder of a public highway, must be attended by its driver. However, the vehicle need not be attended while its driver is performing duties which are incident and necessary to the driver's duties as the operator of the vehicle.
(d) For purposes of this section -
(1) A motor vehicle is attended when the person in charge of the vehicle is on the vehicle, awake, and not in a sleeper berth, or is within 100 feet of the vehicle and has it within his/her unobstructed field of view.
(i) Has been designated by the carrier to attend the vehicle;
(ii) Is aware of the nature of the hazardous materials contained in the vehicle he/she attends;
(iii) Has been instructed in the procedures he/she must follow in emergencies; and
(iv) Is authorized to move the vehicle and has the means and ability to do so.
(3) A safe haven is an area specifically approved in writing by local, State, or Federal governmental authorities for the parking of unattended vehicles containing Division 1.1, 1.2, or 1.3 materials.