The OHSAS18001 management standard has existed for a number of years as the way that organization’s demonstrate their competence in Health and Safety management.
This standard has now been withdrawn and has been replaced by ISO45001:2018. Currently organizations are in the process of Migrating to this new standard, and holders will need to migrate to ISO45001:2018 by March 2021
Where organisations demonstrate to a Certification Body (CB), like BSI, that they have successfully completed the migration process, the CB may certify them to the standard.