According to the U.S. Environmental Protection Agency’s National Emission Standards for Hazardous Pollutants (NESHAP) for benzene (EPA 40CFR61, March 1990), petroleum refineries must enclose their oil/water separators with a floating cover system or a fixed cover with a closed-vent system followed by an emission control device. 

With fixed cover systems, refineries must consider possible hazards including safety devices, access, monitoring equipment, instrumentation and separator equipment.  Purging, enclosure and vapor control should also be taken into consideration when designing a control and treatment system.

Ignition Sources
Vapor Space Purging
Purge Gases
Cover Material
Vent Devices
Vapor Control Device
Enclosed Combustion Devices
Vapor Recovery Devices
Flare Devices