Health, Safety, Security and Environment

What is the difference between primary and secondary spill containment?

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Q:What is the difference between primary and secondary spill containment?

A:When storing oil and hazardous chemicals, we are obliged under the law (EPA, OSHA, NIOSH, NOAA, and so forth) to ensure that these substances are stored properly and securely so they do not escape their containment and pollute the environment.There are two types of containment for these substances: primary and secondary. The purpose of each type is different and so is the way they’re used.

Primary vs. Secondary

Primary containment is the receptacle in which the hazardous substance is contained during normal operation. It confines the substance and, when all goes well, does not allow it to spill or leak outside of the container.

Secondary containment, on the other hand, is intended to contain a spill or leak when the primary containment fails. Unlike primary containment units, secondary containment is not continuously filled with the substance and only acts as a safeguard.

Generally, the line between primary and secondary containment is fairly clear-cut, but, some solutions can be used as both. Membranes, for instance, could be used to line a container like a transformer or a tank, in which case it would act as secondary containment. However, when that same membrane is used to line a pond (frack water or wastewater) or a landfill, it acts as primary containment.

Emptying Containers

The way the containers are emptied is another major difference between the two types. Emptying a primary containment is a routine operational procedure, requiring us to train our employees how to handle the substance (WHMIS), while emptying secondary containment is an emergency procedure, requiring us to train our team in emergency response.


Primary containment comes in different sizes and types. Some is fairly small and mobile, like drums and totes, and comes to us pre-filled by the manufacturer. Other primary containment receptacles are way larger and immobile, such as oil holding tanks, and we generally fill and empty them on our premises during our operational processes.

Secondary containment reflects the size and nature of the substance stored in the primary container. It should be big enough to contain the spilled substance, and the material has to be compatible with the substance. Secondary containment units, like spill pallets and berms, are usually found beneath or around the primary containment. A notable exception is the double wall tank, where the secondary containment wraps around the primary containment.

Passive vs. Active Containment

While the primary containment can only be passive, not depending on anybody to deploy them, the secondary containment can be either active or passive. Active secondary containment relies on our employees to physically deploy and engage it. The most common example of these active containment measures are socks, booms, pads, “kitty litter,” Oil Solidifying Polymers, and retractable containment

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