30 CFR § 817.66 - Use of explosives: Blasting signs, warnings, and access control.
(1) Conspicuously place signs reading “Blasting Area” along the edge of any blasting area that comes within 100 feet of any public-road right-of-way, and at the point where any other road provides access to the blasting area; and
(2) At all entrances to the permit area from public roads or highways, place conspicuous signs which state “Warning! Explosives in Use,” which clearly list and describe the meaning of the audible blast warning and all-clear signals that are in use, and which explain the marking of blasting areas and charged holes awaiting firing within the permit area.
(b) Warnings. Warning and all-clear signals of different character or pattern that are audible within a range of 1/2 mile from the point of the blast shall be given. Each person within the permit area and each person who resides or regularly works within 1/2 mile of the permit area shall be notified of the meaning of the signals in the blasting notification required in § 817.64(a).
(c) Access control. Access within the blasting areas shall be controlled to prevent presence of livestock or unauthorized persons during blasting and until an authorized representative of the operator has reasonably determined that -
(1) No unusual hazards, such as imminent slides or undetonated charges, exist; and
(2) Access to and travel within the blasting area can be safely resumed.