Externally Flanged Base (EFB) tanks are the most cost effective solution if a sectional tank is required. They have the additional advantage that the tank can be fully drained quickly and without pumps.

EFB tanks are designed to be installed in situations where there is sufficient access to the base and sides of the installation to allow interconnection of the panels from outside the tank.

A clearance space of a minimum of 500mm is required on all sides and there must be sufficient headroom above the tank for opening the manway cover, we recommend 750mm.

The base support structure must be constructed to allow the installer an access space of 500mm to the flanges from below. The base fixings are only accessible from the underside of the tank. Consequently the tank cannot be sited on a solid slab but instead must be raised on piers (or a combination of piers and RSJs) which directly support the flanges which join the tank panels together.

The supports should run in one direction only and must be at least 300mm longer than the overall length of the tank to support the external vertical flanges.

The final base support system must be flat and level and strong enough to support the weight of the tank when full without movement.

The base structure for EFB tanks must be to the following tolerances:

• 2mm in any metre
• 6mm in any 6 metres
• Maximum beam deflection 1:500

Pier or RSJ supports need to be spaced at 1,000mm centres for metric sectionals and 1,220mm centres for imperial sectionals.

In cases where space restricts the access to the sides of a tank a TIF tank should be considered.