We all want to please the boss. But sometimes, you just have to say no. Those times include when your boss asks you to do something that damages the environment, violates the law, or is unsafe.
Typically when a supervisor asks a subordinate to do something that is unsafe (or damages the environment or violates the law), it’s a matter of simple oversight or not having your more detailed knowledge of that particular job. Any good supervisor expects you to speak up and will be glad you did.
But what if you tell your supervisor the act is unsafe and your supervisor insists you proceed anyhow? Maybe your supervisor is tired or feeling time-pressured and so isn’t thinking clearly. Make that assumption, rather than leaping to the conclusion your supervisor doesn’t care if you are injured or killed. Or maybe you misread the situation and there isn’t actually a safety issue; ask your supervisor to explain.
If you disagree with the explanation, ask if the two of you can meet with another supervisor or the safety director. Try to work things out, just don’t compromise safety to do it.