EPA and OSHA put out an Alert in 2007 regarding the use of Excess Flow Valves (EFV) as a “safeguard”. Although that alert has been “archived” the failures we see today align with what that alert warned us about 16 years ago!
While excess flow valves (EFV) are in extensive service and have prevented numerous pipe or hose breaks from becoming much more serious incidents, experience has shown that in some cases the EFV did not perform as intended, usually because of misapplication. Also, undue reliance must not be placed on EFVs as the sole or primary protection to control accidental chemical releases from tanks or piping.
Undoubtedly, our #1 finding in using EFVs is a “design error”! As stated in the alert, the NPGA stated…
Piping system restrictions, such as pipe length, branches, reduction in pipe size, and partially closed shut-off valve, could limit the flow rate through the EFV.
So, the Compressed Gas Association (CGA) explicitly calls out this design flaw in its standard for anhydrous ammonia. (emphasis by me):