When dealing with the use, handling, dispensing and storage of hazardous liquids, the concept of secondary containment is often discussed. In fact, several regulatory agencies have established rules for secondary containment of hazardous liquids. The primary agencies who have established these rules are:
- International Code Council (ICC) – the organization responsible for the International Building Code and International Fire Code (IBC, IFC)
- State and local Building and Fire Codes – for example the Ohio Building Code (OBC), and the Ohio Fire Code (OFC). Most state and local codes are based on the regulations set forth in IBC and IFC respectively
- National Fire Protection Association (NFPA)
- Occupational Safety and Health Administration (OSHA)
- Environmental Protection Agency (EPA)
The majority, or at least a significant minority, of chemical plants are using or storing hazardous chemicals throughout at least a portion of their facilities. With this in mind, a basic understanding of the secondary containment requirements is necessary to properly mitigate the effect of a catastrophic tank rupture. There are several accepted methods for secondary containment; the most common of which are containment by using a double wall tank, containment by remote impounding, and containment by an open top diked area. Each of these methods has its own specific design criteria in order to be in compliance.
The basic requirement for containment is that the volume of the secondary containment must equal or exceed the volume of the largest tank within the containment area. This volume needs to be adjusted for the reduction in volume caused by the presence of other tanks, pumps, pump pads and accessories located within the confines of the containment area. Outdoor containment (except containment via double wall tank) is also required to allow for the volume of a prescribed rainfall event, for example 24 hours of a 25 year storm. Indoor containment in a sprinklered building carries a significant additional volumetric requirement in the event of a tank rupture and concurrent activation of the sprinkler system. The IFC states that the secondary containment shall, in addition to the largest tank volume, be able to contain a volume of sprinkler water for 20 minutes for an area of 3,000 square feet or the plan area of the dike, whichever is smaller. That could amount to a containment volume requirement in the range of 21,000 gallons in addition to the volume of the largest tank. Adding tanks to tank farms will require a recalculation to verify that sufficient containment volume exists. To insure that the containment is crack or gap free, there are also inspection requirements. These vary state to state. Regarding the enforcement of the above, as of November 2015 OSHA has been given the authority, and has been exercising the authority to increase its fines by 82% for violations. This large increase is primarily a reaction to the fact that OSHA fines have not increased since 1990.
Many owners have requirements that exceed the minimums as prescribed above. For example, some owners require containment of 110% of the volume of the largest tank within the containment area. As is the case with most designs, the most stringent requirement (EPA, IBC, IFC, plant standard, etc.) should govern.
This is not intended to be a complete design guide of secondary containment systems, merely a small insight into some of the requirements set forth by regulatory agencies. Some items such as tank spacing, maximum wall heights and materials of construction need to be considered when designing or modifying a secondary containment system. As with other design considerations, consultation with a design professional will help insure your secondary containment system is designed properly and in compliance.