46 C.F.R. § 197.535 – Regulated areas.

(a) Based on the employer's evaluation of the environmental monitoring, whenever the airborne concentration of benzene within an area exceeds or reasonably can be expected to exceed the permissible exposure limits, the person in charge shall mark the area as a regulated area.
(b) The person in charge shall restrict access to regulated areas to authorized persons wearing an appropriate respirator in compliance with § 197.550 and the personal protective clothing and equipment in compliance with § 197.555. The person in charge shall not allow any person to enter a regulated area without another individual in the vicinity to perform rescue or call for help. The second individual must maintain communication with the one entering the regulated area or keep that individual in sight. Also, the second individual must be located at the point of access during confined space entry.
(c) The boundaries of regulated areas must be indicated by barricades, other devices, or by painted areas on the vessel. A sign bearing the following legend in letters at least three inches high (except for the words “DANGER—BENZENE”, which must be printed in letters at least 50 percent larger than the other words) must be posted at each access to the regulated areas:
DANGER—BENZENE REGULATED AREA CANCER CAUSING AGENT FLAMMABLE—NO SMOKING AUTHORIZED PERSONNEL ONLY RESPIRATOR REQUIRED