EPA/CARB COMPLIANT. 2-stage fuel cap is required on all portable fuel tanks. A portable fuel tank is designated as 12-gallon fuel capacity and less.. Audible 'Click" signals cap is sealed on the neck fill. Tether secures cap to fuel tank while refueling. Auto "Self-Venting" pressure feature vents tank at 5 PSI (Min) when center pup-up vent is in open position. Manual momentary pressure relief valve relieves tank pressure prior to cap removal for refueling or connecting/disconnecting fuel line assembly. Positive vent closure for storage and transportation, designed to override of the automatic "self venting" and manual momentary pressure relief function