ISO 45001 was launched in 2018 and is replacing BS OHSAS 18001 as the accepted Health and Safety standard. If you have BS OHSAS 18001 you have until March 2021 to convert your system, after which your current certification will no longer be valid.
Certification to ISO 45001 is a demonstration to your customers and employees that you take Health and Safety matters seriously. As with BS OHSAS 18001, it forces you as a business to formally address the key Health and Safety issues within your organisation.
ISO 45001 is written in the same format as other ISO standards such as ISO 9001 and ISO 14001, and is therefore fairly easy to integrate into a combined management system if required.