Area on deck within which a parted mooring line can whip back; standing in this zone has killed many seafarers.
Regulatory detail & full definition
OCIMF MEG4 (2018) replaced the old fixed snap-back zone markings (often inaccurate) with a 'snap-back hazard area' covering the entire mooring deck — every line is treated as a potential snap-back source. Crew working mooring lines must keep all body parts out of the bight and direct line of fall. Required marking under MLC 2006 Reg. 4.3 + ISM Code Element 6.