Lindak, ISO 45001 will not replace BS OHSAS 18001. Because ISO 45001 will be a ISO creation, but CSA Z1000, BS OHSAS 18001, BS OHSAS 1804, ANSI Z10, GOSH..., AS/NZ..., etc, are national OSHMS standards. Bye.
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Let's live the international, multilingual and free OSHMS standard: ILO-OSH 2001!
Of course OHSAS 18001 isn't an official international standard. There had been some attempts though to get there. I think, once ISO 45001 is ready, many companies will move from OHSAS 18001 to ISO 45001 - and the consultants as well as the certification bodies will enjoy more business.
I also like ILO-OSH. One important feature of ILO-OSH: It's free! Any employee in a company can read it in the internet. In contrary to that, employees in OHSAS 18001 (ISO 45001 etc.) certified companies have to pass some hurdles to read about their employer's commitments in copyrighted standards. The lack of such hurdles may be one of the many reasons why employers do not feel comfortable with ILO-OSH.
This is a problem, because I know of OH&S management manuals where employers did everything not to make the paragraph 4.4.3.2 "Participation and consultation" of OHSAS 18001:2007 known to their employees. ISO 45001 won't solve that problem. Worse, the certification boddies take sides: The employers are their customers, not the employees. (Exception: Dutch certification bodies who use the SCCM scheme for audits also let the employees participate in audits in a systematical way. See also: annex 6, page 57-58 in "O11-SCCM_N110830_cert.schema_OHSAS_18001_ENG_7Feb13")
The solution to that problem: At least the employees' representatives should know the OH&S management standard very well by which their sites are certified. They also should know the SCCM, as their audit scheme shows, that balanced audits
are possible.
Sadly, many companies still managed to deter employees from founding a works council. That is illegal in my country (Germany), but it still happens often enough. And for the lucky ones (employees) who are represented by a works council, many works councils are afraid to dig into such "complex" standards, even though e.g. OHSAS 18002:2008 is an excellent and easy to understand textbook on OH&S management.
I hope that the spirit of ILO-OSH will live on in ISO 45001 too - if the unions who participate in developing the standard do a good job. The BSI even provides a table which shows, that OHSAS 18001 is strongly influenced by ILO-OSH. ILO-OSH at least will serve as a good banchmark for ISO 45001.