Sturdy manhole suitable for MC 306 and non-specification applications. Provides pressure actuated venting through the 10″ fill opening as required by DOT, NFPA 385 and 407. Normal vent is provided with the #37X. Emergency venting thru the 10″ fill opens at 3 PSIG and goes to full open at 5 PSIG. At 5 psig the 10″ fill vents 240,000 SCFH. Standard gaskets are NC757 with other materials available.