ULC 661

This Standard sets forth the minimum requirements for the construction and performance of overfill protection devices for installation in aboveground and underground flammable liquids and combustible liquids storage tanks.

The overfill protection devices shall be designated as Class I or II in accordance with the liquids they are intended to contain, as listed below.
A Class I devices shall be suitable for use with flammable liquids and combustible liquids, described in Clause 1.1.1; and
B Class II devices shall be proven suitable for use with the specific liquid(s) for which the device is intended, by additional testing in accordance with Section 5.4, Immersion Test, using the specific liquid(s) .

An overfill protection device shall function as one of the following:
A Automatic sensing device for interconnection with shutoff equipment or alarm devices acceptable to the authority having jurisdiction;
B Automatic overfill shutoff device of float valve or other mechanical type; or
C Overfill alarm devices of the audible or combined audible and visual types. The shutoff device referred to in Sub-clause 1.4 (B) shall operate according to its type of application:
*Pressure filled; or
*Gravity filled.