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!