OISD Tank Farm Rules


General Classification of Petroleum Products

Petroleum products are classified according to their closed cup Flash Points as given below.

Class – A Petroleum : Liquids which have flash point below 23 deg. C.

Class – B Petroleum : Liquids which have flash point of 23 deg. C and above but below 65 deg. C

Class – C Petroleum : Liquids which have flashpoint of 65 deg. C and above but below 90 deg. C

Excluded Petroleum : Liquids which have flash point of 93 deg. C and above.


7.1 : General considerations

7.1.1 Dyked Enclosures;

  1. Petroleum storage tanks shall be located in dyked enclosures with roads all around the enclosure.
  2. Aggregate capacity of tanks located in one dyked enclosure shall not exceed following values:
  3. 60,000 cum. for a group of fixed roof tanks.
  4. 120,000 cum. for a group of floating roof tanks.
  5. Fixed cum floating roof tanks shall be treated as fixed roof tanks.
  6. However in case these tanks are provided with windows opening on the shell and these windows will not get blocked in any case, then these may be considered as floating roof tanks.
  7. If a group of tanks contains both fixed and floating roof tanks, then it shall be treated as a group of fixed roof tanks for the purpose of above limits.
  8. Dyked enclosure shall be able to contain the complete contents of the largest tank in the dyke in case of any emergency.
  9. Enclosure capacity shall be calculated after deducting the volume of tanks (other than the largest tank) and the tank pads within the dyke upto the height of the enclosure.
  10. A free board of 200 mm above the calculated liquid level shall be considered for fixing the height of the dyke.
  11. The height of tank enclosure dyke (including free board) shall be at least 1.0 m and shall not be more than 2.0 m above average inside grade level.
  12. The dyke wall made up of earth, concrete or solid masonry shall be designed to withstand the hydrostatic load.
  13. Earthen dyke wall shall have not less than 0.6-meter wide flat section on top for stability of the dyke wall.
  14. For excluded petroleum, the capacity of the dyked enclosure should be based on spill containment and not for containment on tank rupture.
  15. The minimum height of dyke wall in case of excluded petroleum shall be 600 mm.
  16. Separation distances between the nearest tanks located in separate dykes shall not be less than the diameter of the larger of the two tanks or 30 meters, whichever is more.
  17. Process equipment should not be located inside the dyke.
  18. Pump stations and piping manifold should be located outside dyke areas by the side of roads.
  19. Tanks located overhead shall meet safety distances and shall also have dyked enclosure of RCC construction and provided with efficient drainage system for the dyke enclosure.
  20. Grouping of petroleum products for storage shall be based on the product classification.
  21. Class-A and / or Class-B petroleum may be stored in the same dyked enclosure.
  22. Class-C petroleum should preferably be stored in separate enclosure.
  23. However, where Class-C petroleum is stored in a common dyke along with Class-A and/or Class-B petroleum, all safety stipulations applicable for Class-A and/ or Class-B respectively shall apply.
  24. Excluded petroleum shall be stored in a separate dyked enclosure and shall not be stored along with Class-A, Class-B or Class-C petroleum.
  25. Tanks shall be arranged in maximum two rows so that each tank is approachable from the road surrounding the enclosure.
  26. This stipulation need not be applied to tanks storing excluded petroleum class.
  27. Tanks having 50,000 cum capacity and above shall be laid in single row.
  28. Fire walls; In a dyked enclosure where more than one tank is located, firewalls of minimum height 600mm shall be provided to prevent spills from one tank endangering any other tank in the same enclosure.
  29. A group of small tanks each not exceeding 9 meters in diameter and in all not exceeding 5,000 cum in capacity shall be treated as one tank for the provision of firewall.
  30. For excluded petroleum product storage, firewall of height not less than 300 mm shall be provided by limiting the number of tanks to 10 or the capacity of group of tanks to 5,000 cum whichever is lower.
  31. The tank height shall not exceed one and half times the diameter of the tank or 20 m whichever is less.
  32. For the installations covered under Oil Mines Regulation, the maximum height of the tank, dyke requirements etc. shall be as per Oil Mines Regulations
  33. Piping from / to any tank located in a dyked enclosure should not pass through any other dyked enclosure.
  34. Piping connected to tanks should run directly to outside of dyke to the extent possible to minimise piping within the enclosures.
  35. The minimum distance between a tank shell and the inside toe of the dyke wall shall not be less than half the height of the tank.
  36. There shall be access on all four sides of each dyke area and roads should be linked to minimize the effect if one road is cut off during the fire.
  37. Separation Distances between tanks / offsites facilities;
  38. The following stipulations shall apply for the separation distances for above ground tanks storing petroleum:
  39. For larger installation, minimum separation distances shall be as specified in Table- 3 and Table-4.
  40. The tables are applicable where total storage capacity for Class-A and Class-B petroleum products is more than 5000 cum or the diameter of Class-A or Class-B product tank is more than 9 meters.
  41. For smaller installation, minimum separation distances shall be as specified in Table-5.
  42. This table is applicable where total storage capacity of Class-A & Class-B is less than 5000 cum and diameter of any tank storing Class-A and Class-B petroleum product does not exceed 9 meters.
  43. Table-5 shall also be applicable for the installation storing only Class-C petroleum.
  44. Excluded petroleum should be treated as Class-C petroleum for the purpose of separation distances and Table – 5 shall be applicable for their separation distances.
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