Potential ignition sources exist in the vapor space beneath the fixed covers on oil/water separators.  An explosion may result when a chemical, electrical or mechanical heat energy source generated in or around the separator brings volatile hydrocarbon vapor (a combustible material) to its flash point in the presence of oxygen (an oxidizing agent).   

Chemical heat energy is created when metallic separator components made from carbon steel or aluminum corrode.  Hydrogen sulfide corrodes carbon steel to produce an iron sulfide scale.  When the oil/water separator is taken off-line, moisture evaporates, allowing the scale to dry out and creating an environment ripe for spontaneous ignition.  Similarly, aluminum in contact with methylchloride forms pyrophoric aluminum alkyls, which may violently ignite when exposed to air. 

Electrical heat energy originates either inside (at motors, drives and controls) or outside (static electricity or lightning) oil/water separators.  Correctly sizing motor enclosures for each application and situating switchgear and motor starters far from the oil/water separator area helps minimize the risk of generating excess electrical energy.  Electrical devices and controls located in the immediate vicinity of the separator should be housed in explosion-proof enclosures. 

Mechanical heat energy results from frictional resistance from belt or friction disc variable speed drives or improperly sized hydraulic drives on the oil/water separators.  Other potential ignition sources from mechanical heat energy include mechanical devices that remove floating oils from the surface of the separators or settled solids in the bottom of the units.  All equipment should be grounded.

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