Internal and external parties

The reason that ISO 45001 has you identify internal and external parties in clause 4.2 is so that you can identify the needs and expectations that each of these parties has that you need to incorporate into your OHSMS. So, if you identify a government agency and an external party, and identify that they have a law that they expect you to meet on chemical handling; this would become a part of the processes within your OHSMS. In short, the effects of these interested parties on the OHSMS is that they identify the requirements that need to be included int eh OHSMS processes.

You can learn more about the requirements for interested parties in the article: Determining interested parties according to ISO 45001, https://advisera.com/45001academy/blog/2018/03/14/determining-interested-parties-according-to-iso-45001/