40 CFR § 279.61 - Restrictions on burning.
(a) Off-specification used oil fuel may be burned for energy recovery in only the following devices:
(2) Boilers, as defined in § 260.10 of this chapter, that are identified as follows:
(i) Industrial boilers located on the site of a facility engaged in a manufacturing process where substances are transformed into new products, including the component parts of products, by mechanical or chemical processes;
(ii) Utility boilers used to produce electric power, steam, heated or cooled air, or other gases or fluids for sale; or
(2) Used oil burners may aggregate off-specification used oil with virgin oil or on-specification used oil for purposes of burning, but may not aggregate for purposes of producing on-specification used oil.