I have spent my career working with flammable liquids, and those who have followed my writings on the topic understand why I have stopped using 1910.106 as my baseline flammable liquid safety standard and instead began using either the IFC or NFPA 30. I have been involved in several serious events where atmospheric storage tanks had been “manifolded” together (oftentimes for reasons unknown to facility personnel). OSHA’s 1910.106 does NOT prohibit manifolding tank vents to a common discharge location; it merely provides minimum design for manifolding vents…
1910.106(b)(3)(iv)(e)
When tank vent piping is manifolded, pipe sizes shall be such as to discharge, within the pressure limitations of the system, the vapors they may be required to handle when manifolded tanks are filled simultaneously.
However, the International Fire Code (IFC) and NFPA 30 PROHIBIT manifolding atmospheric storage tanks containing flammable liquids, “unless required for special purposes such as vapor recovery, vapor conservation or air pollution control.”
IFC, Chapter 57
5704.2.7.3.5 Manifolding. Tank vent piping shall not be manifolded unless required for special purposes such as vapor recovery, vapor conservation or air pollution control.
NFPA 30, Chapter 27
27.8.1.4 Manifolding of vent piping shall be prohibited except where required for special purposes such as vapor recovery, vapor conservation, or air pollution control.
The manifolding of atmospheric storage tanks requires the manifold to be designed to handle the additional pressure generated by heating the flammable or combustible liquid. This additional pressure could cause pressure to build up in other tanks or in the piping system, causing leaks or failure of other tanks or piping.