Well I told you last week that I would scare the !@#$ out of a lot of you, so here it goes. Nitrogen can be your ignition source if it is NOT applied and used properly.
If you took 10 minutes and watched the CSB video I suggested you may know where I am going with this. As the CSB demonstrated in their video on the Barton Solvent fire in KS several years ago, the air entrained in the hose as it was switched from compartment to compartment, traveled thru the pipe to the inlet of the tank. At Barton’s the inlet line was always below the liquid level, which in 9 out of 10 times lowers the risks associated with the transfer of non-conductive flammable liquids. But in the set up at Barton’s this allowed the entrained air to bubble up through the non-conductive solvent, which acted as an agitator and super charged the non-conductive liquid. As the liquid became charged, the metal level float sitting on the surface became charged. Just a small gap in the linage assembly allowed a spark to jump from the float to the float cable assembly. Being that this occurred at the liquid surface there was plenty of vapor to make an ignitable mixture (for more on LEL and MOC see my other post in Flammable Liquids).
Well nitrogen will do the exact same thing that air did at Barton solvents. A lot of plants use nitrogen to blow their lines after unloading a RRCar or TTruck or even before a line break permit is issued. If your tank inlet line introduces the nitrogen gas so that it passes through the liquid the gas will agitate the liquid and super charge it to the Minimum Ignition Energy and if this occurs BEFORE enough nitrogen can inert the head space of the vessel we have the perfect setup for ignition.
Nitrogen being introduced into the headspace is the SAFE way to inert a vessel, but bubbling it up through the liquid, either through a dip leg that extends to 6” from the bottom of the tank or an inlet that is below liquid level is BAD NEWS and should not be a allowed without an extensive safety and engineering review. Just blowing nitrogen into a tank can not only be a waste of money, it can actually create a hazard within the flammable atmosphere.
Who’da thought!!!!!