Beside legal requirements, the OHSAS 18001 mentions "other requirements" and that can be contractual requirements, requirements of some associations to which the company belongs to, requirements of some interested parties, such as nongovernmental organizations, etc.
Other requirements are basically all requirements that the organization has agreed to for some reason. For more information, see:
- How to identify and comply with legal requirements in OHSAS 18001 https://advisera.com/18001academy/blog/2015/06/24/how-to-identify-and-comply-with-legal-requirements-in-ohsas-18001/
- OHSAS 18001: Advice to ensure you meet regulatory requirements https://advisera.com/18001academy/blog/2015/07/29/ohsas-18001-advice-to-ensure-you-meet-regulatory-requirements/