http://www.peakhse.co.uk/news/162/iso-45001-draft-out-for-comment

[...] BS OHSAS 18001 is still valid and it is envisaged may well be for some time after the new ISO Standard is published. Companies will still benefit from implementing and certifying against BS OHSAS 18001. [...]

 
http://isqem.wordpress.com/2014/07/27/ohs-management-systems-and-impact-on-business-practices/

[...] It is hoped that the introduction of the ISO 45001:2016 standard will have a positive impact on global acceptance to OHS. Time will tell if the present ISO working committee have got it right, if not it could turn out to be a basic cosmetic makeover of OHSAS 18001, with very little impact.

If you consider there are three major changes to ISO management standards including, Quality and Environment in 2015 and OHS in 2016, you have to question when, or if, your organisation should make the transition. As with any systems changes you will need to take into account aspects such as, development cost, staff training and re-certification.

It might pay to hold back on any certification and changes until after the OHS standard is officially released in 2016. Then you can make one integrated change across your management systems, limiting any financial, time or operational impacts and make implementation feasible. [...]