Many chemical processes that are covered under OSHA’s PSM and EPA RMP rules utilize one of the most popular forms of passive mitigation ever known…Diking. However, on the other hand, many of the facilities have not included their dikes in their Process Safety Information (PSI) or their Mechanical Integrity Programs (MIP).
For the PSI portion, the facility should have on hand the documentation that the dike is SIZED PROPERLY, how it is constructed, and I also like to see that the facility has taken into consideration the construction method when considering the Worst Case Release scenario. In other words, will the dike survive a catastrophic failure of the vessel or will the force of the material from the tank push the dike wall over? As for sizing, the facility should document what “sizing requirements” they used when designing the dike. One specific dike design that I work with on a regular basis is for Flammable Liquids. 1910.106 has some specific diking requirements that differ from EPA’s “largest tank + 10%”.
As for the MIP part, we expect to see that the Dike is in some type of routine inspection program, even if it is just a visual inspection on “operator rounds”. But the dike should be tested from time to time to check for leaks and to ensure the walls maintain their strength. A facility should have a written maintenance procedure for this testing and should train those who will be performing the test(s).
Some things to keep in mind about your diking:
1) ANY change to a dike or that can impact a dike’s capacity MUST go through the MOC process. We have seen situations where a non-PSM covered tank was added to a dike that was part of the covered process. Since the tank being installed was NOT part of the covered process a MOC was not used for its installation. When it was installed, it’s diameter was such that now the dike did not meet 1910.106, as the new tank took up too much volume, and thus the dike could no longer hold the entire contents of the largest tank.
2) Dikes have drains and most of the time these drains are CLOSED; however, there have been spills that reach the ground because a drain valve was left open. I have written about car-seal programs and it is my opinion that dike drain valves should be included in any car-seal program to ensure they are not inadvertently opened or left open.
3) Diking should be OFF limits! This means no one can use dike walls as pipe rack foundations, drill into dike flooring or walls, dikes can not be used as storage areas, etc.