49 C.F.R. § 230.107 – Tender frame and body.

(a) Maintenance. Tender frames shall be maintained in a safe and suitable condition for service.
(b) Height difference. The difference in height between the deck on the tender and the cab floor or deck on the steam locomotive shall not exceed 1 1/2 inches.
(c) Gangway minimum width. The minimum width of the gangway between steam locomotive and tender, while standing on tangent track, shall be 16 inches.
(d) Tender frame condemning defects. A tender frame with any of the following defects shall be removed from service immediately and repaired:
1. (1) Portions of the tender frame or body (except wheels) that have less than a 2 1/2 inches clearance from the top of rail;
2. (2) Tender center sill that is broken, cracked more than 6 inches, or permanently bent or buckled more than 2 1/2 inches in any six foot length;
3. (3) Tender coupler carrier that is broken or missing;
4. (4) Tender center plate, any portion of which is missing or broken or that is not properly secured; or
5. (5) Tender that has a broken side sill, crossbearer, or body bolster.