They were test to assure safety of human life, and women couldn’t pass them. So they lowered them. The biggest one was being able to carry a person of a specific mass out of an area within a specific amount of time, with all your gear on, in a smoke filled room. Few men were able to pass it, and almost no women. So they lowered the amount of weight and upped the time limit. Sometimes even just flubbed the women passing so they could reach diversity goals.
People will die because of it, but hey…women firefighters! WOO HOO!
Now the thing that’s really sexist, is denying sexual dimorphism exists within the human species and that men --in general-- can be better suited among the general populace for specific tasks when it comes to simple brute strength.