Electrical Code…
Equipment sealed against the entrance of an external atmosphere where the seal is made by fusion, for example , soldering, brazing, welding, or the fusion of glass to metal.
Informational Note: For further information, see ANSI/ISA-12.12.01-2013, Nonincendive Electrical Equipment for Use in Class I and II, Division 2, and Class III, Divisions 1 and 2 Hazardous (Classified) Locations
(National Electrical Code® 100-1)