ES&H Manual

Flammable Gas Supplement




Chapter 4 – Electrical Classification Guidelines




These guidelines are based on common gas system installations at Jefferson Lab which have been analyzed.  The classification shall be determined for each specific installation.  All areas are assumed to be NEC Class 1, Group D.


1)     Enclosed gas storage and mixing sheds are Division 2.  This is based on adequate ventilation, this standard, and that a flammable mixture is likely to be present in the atmosphere less than ten hours per year.


2)     A sphere with a diameter of 1.5 meters around outdoor vents is Division 1.  A sphere with a diameter of 3 meters is Division 2.  Generally there would be no electrical equipment in this area.


3)     A sphere with a diameter of 1 meter is Division 1 around indoor vents.  A sphere with a diameter of 2 meters is Division 2.












ESH&Q Division

Jack Segal

June 15, 2011

June 15, 2016



This document is controlled as an on line file.  It may be printed but the print copy is not a controlled document.  It is the user’s responsibility to ensure that the document is the same revision as the current on line file.  This copy was printed on 6/14/2011.