It's really a pity when an expert doesn't understand the intent of the documents being discussed and the difference between shall and should.
Here's a small example of the difference between the ILO-OSH and OHSAS 18001
ILO-OSH 2001; 3.3.1. The employer should have overall responsibility for the protection of workers' safety and health, and provide leadership for OSH activities in the organization.
OHSAS 18001; 4.4.1 Resources, roles, responsibility, accountability and
authority - Top management shall take ultimate responsibility for OH&S and the OH&S management system.
In use, the word "should" allows one to choose either to do or not to do, whereas the word "shall" doesn't allow that choice, "shall" is a requirement to do what is required.
Simply put, any organization can claim to meet the guidelines of ILO-OSH 2001 while at the same time exercising the option (should) to pick and choose which portions it wants to do or not do.
Because an organization "voluntarily" chooses to apply either the Z-10 or 18001 as its method for managing OHS issues it, the organization, makes either one of those documents a mandate that it must meet by fulfilling the "shalls" contained within them. This has nothing to do with the law or legislative requirement to do so. Because neither Z-10 or 18001 allow an organization to exclude itself from meeting all requirements (shalls), the documents have greater strength.
Additionally it is much easier to audit and verify that "shalls" have been met than "shoulds" for purposes of 3rd party certification...which is probably what you might be looking for.
Here is another part of 18001;
OHSAS 18001 now refers to itself as a standard, not a specification, or document, as in the earlier edition. This reflects the increasing adoption of OHSAS 18001 as the basis for national standards on occupational health and safety management systems.
OHSAS 18001 is being used by multiple nations as the template for OHS systems....Multiple nations means International and it is a standard so therefore it is an International Standard. Sooner or later the "duh" factor has to kick in on this.
I work for a major 3rd party certification body and I am an OHS management systems auditor and I do not believe that we do ILO-OSH 2001 certification, we do perform OHSAS 18001 and we will perform ANSI Z-10 system certification.
And oh yes, to cut Henria off before she goes completely nuts, my employer's global headquaters is in the United Kingdom and it's called BSI, and yes it is the same BSI that prints the 18001 standard (But there were an additional 40+ other organizations from around the globe that worked on the contents that were not under the control or management of BSI). I was a minor particpant in both ANSI Z-10 and OHSAS 18001, so I've done a bit more than just read them. (If Henria wasn'rt invited to those parties I'm sorry)
All of the documents have strengths and weaknesses, none are perfect. If you have to choose then a correct choice might be what a good majority are choosing.