Debasis Leak detection (tell tale) is to detect leaks at the bottom plate through a channel for identifying the extent of leak, for monitoring the leaks ( both quantum and for assessing the relative degree of safety hazards for equipment and personnel). Leak detection is essential for any tank bottom from consturction and identifying conditions for prepraredness to assess the quantum and risks in operationa and maintenance. Release prevention barrier is to have barrier where all leaks emanated from the tank is contained within a space without release of the tank contents to environment or plant areas or from safety to the plant and nearby public utility and environment areas. RPB - This envisages circumstances where the entire tank content is released instantaneously (for example in the case of an air attack on the tank durnig war times), the release prevention barrier will safeguard to a large extent the fire hazard spreading to nearby equipment or tank's toxic and hazardous content from spreading to the public or to the plant areas and thus preventing a catastrophic crisis due to sudden release of a large quantum of the tank's content to the atmosphere. For Ex: a Tank bund is constructed for Naphtha tank or Methanol tank or Petroleum Class "A" hazard grade tanks to contain all leaks in the bund area amd tjus preventing a major fire or safety hazard spreading to the nearby tanks or plant areas or to the public movement areas. For EX: For Ammonia tanks, the primary aim of release prevention barrier is to contain all ammonia released from the tank inside a concrete dyke wall. Dyke wall is erected to 2/3 height of the tank height so that ammonia is released slowly and the ammonia released does not spread to other areas or the toxic release is diluted before spreading to environment. This could be collapse of a valve or entire ammonia released during war times when aerial attack takes place on the tank. Trust this is of help to you C.V.Srinivasan Nishi Engineers Pvt Ltd Chennai India June 13 E-mail:nishi@vsnl.com >As per API 653/clause4.4.5( Bottom Leak detection), when a >tank bottom is to be replaced, consideration should be given >in installing a Leak Detection (tell-tale) system that will >channel any leak in the bottom to a location where it can be >readily observed from the outside of the tank. At the same >time it talks about RPB (Release Prevention Barrier). > >Please share to have positive interpretation & clarification >of this issue.

For a under tank leak detection and sub grade protection as a suggestion one can consult fig 1-1 to 1-10 from API650. Regards Luis Marques