What is a safe decibel level for humans?

I'm curious to know, what is considered a SAFE decibel level for humans? Is there a specific threshold that we should aim to stay below to protect our hearing? Are there any long-term effects of exposure to high decibel levels that we should be aware of? How can we measure decibel levels accurately to ensure we're staying within safe limits? Are there any industries or situations where special precautions need to be taken to protect workers from excessive noise?