29 C.F.R. § 1918.83 – Stowed cargo; tiering and breaking down.

(a) When necessary to protect personnel working in a hold, the employer shall secure or block stowed cargo that is likely to shift or roll.
(b) In breaking down stowed cargo, precautions shall be taken to prevent remaining cargo from falling.
(c) Employees trimming bulk cargo shall be checked in and out by the job boss. Before securing any reefer compartment, a check shall be made to ensure that no employee remains inside. Frequent checks shall be made to ensure the safety of any employee working alone in a tank or cargo compartment.