Combustible Concentration Reduction (CCR) and Oxygen Concentration Reduction (OCR) are two explosion prevention methods commonly used to control oxidizing agents mixing with combustibles.  Of the two, the CCR method is more sensitive to the volatile hydrocarbon vapor concentration and to the vapor’s flammable range.  It dilutes the vapor space with air to maintain the enclosed atmosphere at a concentration below the lower flammable limit.  Sophisticated instrumentation and monitoring equipment must be used with this type of system. 

Used more often than the CCR system in designing vapor space purging, the OCR system uses gas sources, other than air, to control the oxidant concentration in the vapor space to a point above the upper flammable limit.  Purge gas (inert, steam or fuel) exerts a slight pressure on the system under all operating conditions and flows continuously to maintain the required level of oxygen deficiency.

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