Section 20.2 - Definitions(a)Adequate. Appropriate and sufficient as determined by mutual agreement between the manufacturer and MSHA.(b)Approval. Official notification in writing from MSHA to a responsible organization, stating that upon investigation its lamp has been adjudged satisfactory under the requirements of this part.(c)Explosion-proof compartment. An enclosure that withstands internal explosions of methane-air mixtures without damage to itself or discharge of flame and without ignition of surrounding explosive methane-air mixtures.(d)Permissible. Completely assembled and conforming in every respect with the design formally approved by MSHA under this part. (Approvals under this part are given only to equipment for use in gassy and dusty mines.)Sched. 10C, May 17, 1938, as amended by Supp. 1, 20 FR 2718, Apr. 23, 1955