Maintenance Hole : A structure located on top of an opening in a gravity sewer, or an opening in the top or side of an enclosed vessel to allow personnel entry; also referred to as manhole or manway
NFPA 820 Standard for Fire Protection in Wastewater Treatment and Collection Facilities, 2008 ed. http://www.nfpa.org/codes-and-standards/document-i nformation-pages?mode=code&code=820, (Std: Fr Prac in Wastewater Treatment and Collection Fcilty - Amer) {351 NFC}