Bund Design — Ensuring the Safe Storage of Hazardous Liquids
A bund is essentially a safety feature used in plant designs. The chemicals/liquid which needs to be stored on-site is usually stored in tanks of the required dimensions. The purpose of a bund is to retain the liquid which is stored in the tanks in the case of a spillage or tank failure. Designing a bund is an opportunity for interdisciplinary work because it requires input from a process engineer, a mechanical engineer, and a civil engineer. The image shows a typical bund layout, and certain civil design aspects have been discussed in detail below.
Figure 1: Typical bund layout
Bund Volume
A bund is designed to house 110% of the volume of the largest tank in the bund. This allows for full containment should the tank leak and the entire volume of liquid is released. Should the bund house multiple tanks, the combined volume of 2 tanks can be designed for in the case of simultaneous failure. Many plants house liquids and chemicals which are hazardous for humans as well as the environment and therefore it is important that this liquid is contained and can be pumped into a safe storage container before it infiltrates into the earth or before any humans come into contact with the substance. Therefore, a bund has a concrete surface bed so that no spillage.
Bund Volume
A bund is designed to house 110% of the volume of the largest tank in the bund. This allows for full containment should the tank leak and the entire volume of liquid is released. Should the bund house multiple tanks, the combined volume of 2 tanks can be designed for in the case of simultaneous failure. Many plants house liquids and chemicals which are hazardous for humans as well as the environment and therefore it is important that this liquid is contained and can be pumped into a safe storage container before it infiltrates into the earth or before any humans come into contact with the substance. Therefore, a bund has a concrete surface bed so that no spillage may seep into the earth.
Bund Wall Dimensions
The bund wall needs to be designed to hold the specified 110%. It, therefore, follows that for a lower bund wall, a larger floor area will need to be provided. However, for a larger wall height, a smaller floor area will be required. Depending on the height of this wall, it should be designed as a retaining wall, and the density of the stored liquid should be taken into account. Appropriate reinforcing should be provided.
Bund Dimensions and Safe Passageways
It is important to note that a bund needs to be accessible to humans without a door being added into the walls (in order to prevent leakage out of the bund in the case of a spill). Therefore, staircase access should be provided over the bund wall with a landing at the top. Enough space should be provided around the tanks for personnel access (i.e., 1m around the tanks).
Sump Design
In order to allow for easy extraction should there be a leak, or should there be a rainstorm, a reinforced sump should be provided in the corner of the bund. The surface bed of the bund should be sloped towards this sump. Pumping from this sump should be considered. One option is to use a manual pump in the case of a full sump; however, automated pumping can be designed for.
Epoxy Coating and Tank Bases
Depending on the nature of the chemicals housed, epoxy should be used to coat the bund area. The inner surface area of the bund walls, as well as the slab, need to be coated with this epoxy. However, for further protection, the outer walls of the bund may be coated as well, upon specification from the client. The epoxy should be specifically chosen for the provided chemical specifications of the stored liquid. It is important to bear in mind that some chemicals that may be housed can be corrosive. If this is the case, minimal steel should be used in the design, and a corrosion-resistant coating should be applied to the staircases if a steel staircase is used. Tanks should be placed on top of tank bases. This provides a foundation designed for the specific loading of the tank, and it allows for the tank to be slightly raised off the surface bed. This is further protection to the tank in the case of a leak.
~ Romana Katrakilis
