OHSAS is not actually an ISO standard – however it is basically treated exactly the same by everyone involved with it. It was published after ISO 14001 and that was published after ISO 9001. In many areas, though not all, you can see how the 18001 standard was improved to be better than both of its predecessors.
OHSAS 18001 is a set of requirements for a safety management system. In itself it does not mandate anything about how you actually address safety and if you are generally safe and in compliance with safety regulations then you probably don’t need to make any technical changes in the way you address safety in order to get 18001. What 18001 requires is that you have formal processes for identifying and reviewing safety hazards and that you make a decision about whether any actions are necessary. Often low cost and simple actions are available and management may decide that expensive actions are not justified and the risk to safety is acceptable. Management is made aware of the issues so that responsibility and accountability is clear. With a good safety management system, all issues and potential issues are brought to the attention of management and addressed at a level they choose. This is an incredibly important tool to demonstrate due diligence and, of course, to ensure everyone is safe. Probably, because of its effectiveness, if you don’t do it for the pure value, or because of marketing or customers who prefer you to, then its quite conceivable the it will eventually become a regulatory requirement that you have to follow anyway. OSHA has a “similar” scheme – which if you are attempting then you should consider blending the two together. Both 18001 and OSHA have the same overall goals and controls. One solution should meet two sets of requirements.
Probably you will have appropriate safety expertise in house. Bearing in mind that you currently have an obligation to meet safety regulatory requirements then you have probably got an understanding of everything you need to. What you probably don’t have is the management system expertise to address the need for a low bureaucracy, easy maintenance, effective and value driven system. 18001 is being touted by the safety consultants but their expertise is not in management systems. The requirements can be addressed in a variety of ways and so its important to understand how to read the standard, and wide management experience is essential to ensure a meaningful and effective solution.