30 CFR § 56.13021
High-pressure hose connections
July 29, 2020
Except where automatic shutoff valves are used, safety chains or other suitable locking devices shall be used at connections to machines of high-pressure hose lines of 3⁄4 -inch inside diameter or larger, and between high-pressure hose lines of 3⁄4 -inch inside diameter or larger, where a connection failure would create a hazard.