Seeing an iridescent sheen on the surface of water can be used to detect the presence of an oil spill. The term "oil" applies to both petroleum e.g. crude oil and non-petroleum oils e.g. vegetable oils. Although it is commonly referred to as the “sheen rule” the rule does not only apply to products that sheen.
The VGP does not authorize the discharge of an Environmentally Acceptable Lubricant in a quantity defined as harmful under the “sheen rule”.
Quantity that may be harmful means that it may not: (a) Violate applicable water quality standards; or (b) Cause a film or sheen (an iridescent appearance on the surface of water) upon or discoloration of the surface of the water or adjoining shorelines or cause a sludge or emulsion to be deposited beneath the surface of the water or upon adjoining shorelines.
The addition of dispersants or emulsifiers to oil to be discharged, to circumvent the conditions above, is prohibited. All of these types of discharges must be reported under the “sheen rule” to the National Response Center or if not practicable the Coast Guard or EPA.
Due to their insolubility, the majority of base oils commonly used in lubricants have the potential to result in a film, sheen or discoloration of the surface of the water surface, or a sludge or emulsion, to be deposited beneath the surface of the water if they are released into the water.
Under normal operating conditions (e.g. minimal leakage from operating equipment) the use of a product that has the potential to sheen or leaves a surface film is unlikely to result in an effect being observed. However, if a significant amount of lubricant is leaked into the sea resulting from machinery failure, then a sheen or film is likely to be observed, alerting the vessel operator to the equipment malfunction.
Choosing a lubricant that sheens provides a visual indication to a vessel operator that a discharge has occurred and therefore requires reporting. It also has the advantage of alerting them to the fact that a piece of equipment may have malfunctioned and require repair. It is therefore acceptable for lubricants that have potential to “sheen” to be used in applications that come under the VGP.
Lubricants that contain high molecular weight base oils that sink if spilled into water, may not leave a sheen or film on the waters’ surface. Due to their high molecular weight, however, they may be slow to biodegrade, therefore not meeting the definition of an EAL under the VGP.
Choosing a lubricant that does not sheen, but has the potential to create a film or discoloration on the water or a sludge or emulsion in the water, may leave the vessel operator open to charges of failure to report a spill should a discharge take place that is not reported as required.
For equipment where failure will not result in a significant spill of lubricant e.g. wire ropes, there is no benefit from selecting a product that sheens. In this case, a sheen on the water surface will not alert the operator to a spill, therefore the use of a non-sheen product would be acceptable.