D.C. Mun. Regs. tit. 29, § 249
249.1 A petition to intervene may be made or filed before the commencement of a hearing.
249.2 A petition to intervene may be made orally or in writing. If made orally, the petition must be made on the record with all parties present.
249.3 Each petition to intervene shall meet the following requirements:
(a) Set forth the interest of the petitioner in the proceeding;
(b) Show that participation by the petitioner will likely assist in the determination of the issues in question; and
(c) Demonstrate that intervention will not likely delay the proceeding unnecessarily.
249.4 The hearing examiner may grant a petition for intervention to the extent and upon the terms that the hearing examiner determines shall best serve the interest of justice.
SOURCE: Final Rulemaking published at 35 DCR 8538 (December 9, 1988).