does one need IRB approval for non-govt human research?

Can a researcher who doesn’t have/use govt funds do human subjects research and publish in journals without IRB approval?

It seems difficult to draw a line especially related to sociology or psychology ‘studies’.

I’m sure private funded research for some dramatic and potentially dangerous (or identity revealing) human subjects work SHOULD get IRB approval, but I don’t know if it is legally required.

Then the question becomes at what point is the study not ‘dramatic and dangerous’ enough? Could I just count people walking across the street and publish their behavior without first getting prior IRB approval for the study?