(b) Hazardous Locations. Sewage wells, and the surrounding enclosure shall be classified in accordance with Section 2540.1 and the following:
(1) Sewage Dry Well. The interior of sewage dry wells shall be classified as a Class I, Division 2 location.
EXCEPTION: A sewage dry well shall be permitted to be unclassified provided the following conditions are met:
(A) The well and the surrounding enclosure is treated in accordance with the provisions of the General Industry Safety Orders, Article 108, as a potential confined space; and
(B) The well and surrounding area are provided with a suitable, continuously operating ventilation system to maintain the flammability of the interior atmosphere below 20% of the lower explosive limit (LEL). The air for the ventilation systems shall be supplied from a non-hazardous source. Means shall be provided to automatically de-energize all electrical sources of ignition in the well in the event of ventilation system failure, which would result in the interior atmosphere of the well reading 20% of the lower explosive limit (LEL).
(2) Sewage Wet Well. The interior of sewage wet wells shall be classified as a Class I, Division 1, location.
EXCEPTION: No. 1: A sewage wet well shall be permitted to be classified as Class I, Division 2, location provided the following conditions are met:
(A) The well and surrounding area are treated in accordance with the provisions of the General Industry Safety Orders, Article 108, as a potential confined space; and
(B) The well and surrounding area are provided with a suitable, continuously operating ventilation system to maintain the flammability of the interior atmosphere below 20% of the lower explosive limit (LEL). The air for the ventilation system shall be supplied from a non-hazardous source. Means shall be provided to automatically de-energize all electrical sources of ignition in the well in the event of ventilation system failure, which would result in the interior atmosphere of the well reaching 20% of the lower explosive limit (LEL).
EXCEPTION: No. 2: A sewage wet well shall be permitted to be classified as a Class I, Division 2, location provided the following conditions are met:
(A) The well and surrounding area are treated in accordance with the provisions of the General Industry Safety Orders, Article 108, as a confined space, and
(B) The pump motor(s) is completely submerged in the water whenever the motor is running, and
(C) The motor controller(s) is identified for use in a Class I location or is located outside the classified location, and
(D) The sensors-transducers are identified as intrinsically safe or for use in a Class I location.
(Title 24, Part 3, Section 3-521 - 10.)
