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OSHA, as well as NFPA and IFC, permit a "weak roof-to-shell seam" as the means for emergency venting on an OUTSIDE ABOVE GROUND ATMOSPHERIC storage tank for flammable liquids. This method was vey common in the early days, but has since been replaced with engineered fire vents. This video does an excellent job demonstrating how a "weak roof-to-shell seam" works and why emergency responders MUST be aware of how a flammable liquid tank will vent when involved in a fire scenario. The video at the bottom of the page shows what happens when the "weak roof-to-shell seam" does NOT work as designed. This same video then demonstrates a proper "weak roof-to-shell seam" working and we should take notice of the distance this tank roof travels!
Over the past year or so we have come across several situations where facilities have replaced their flammable liquid storage tanks, which some are used as a “waste tank”. These “waste tanks” fall under EPA’s RCRA rule and apparently these tanks have to be “fully inspected” on a set frequency and when tanks sit directly on their foundation this causes some issues with a “full RCRA inspection”. So it seems that there may be a concerted effort to install new flammable waste tanks, as well as other flammable tanks, on legs so that the bottom of the tank can be visually inspected with ease. Now I am no RCRA expert, but this explanation does make sense; and I have contacted two other businesses where we have seen this and they too stated the same reasons. But each facility viewed these new tanks as a “Replacement in Kind” since the tanks were the same size, same materials of construction, same operations, same nozzle arrangement(s), etc. EXCEPT these new tanks are installed on legs, which CHANGES things considerably and an MOC should have been done. Here’s why…
In the world of process safety we have Safe Upper and Lower limits on a lot of common process parameters, such as pressures, levels, temperatures, etc. Flows on the other hand are quite often over looked as a critical process parameter and when your HHC/EHS is a non-conductive flammable liquid both FLOW and LEVEL must be addressed within the facility’s PSI and SOPs. This article will discuss how safe upper limit on flow and safe lower limit on level can play a huge roll in improving flammable liquid safety and quite possibly PSM/RMP compliance.
A crew was conducting well kill operations on a sweet oil well. A worker was monitoring the return flow to the service rig trough from on top of the rig tank. When the returns became gassier, the return flow was opened to the degasser section of the rig tank and the trough flow was pinched in slightly. The rig manager proceeded to the top of the rig tank stairs where his personal gas monitor immediately began to alarm on high LEL (lower explosive limit). The rig manager looked up to observe both the rig tank and the worker on the rig tank being engulfed in flames. The worker standing on top of the rig tank jumped over the handrail to the ground, and suffered a broken hand from the landing. The flash fire resulted in minor burns to the worker’s face, chest, back and thighs, and extensive burns to the forearms which required skin grafting surgery and 18 days in the hospital. The rig manager jumped off the stairs and was not injured in the event. Ignition source was determined to be a poorly terminated electrical livestock control fence “jumper” wire on the perimeter fencing. CLICK on image below for the full alert from ENFORM.
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