When I went through EMT training in the late 80's we were taught to use "cop'o'meters" and the "Rule of thumb" when dispatched to hazmat situations. "Cop'o'meters" were LEOs at the scene of the spill or whatever. If they were vertical & breathing, it was 'probably' safe to enter the scene. And for fire or gas dispersals, if your thumb, on your outstretched arm, did not cover the whole scene, you were too close. I have, in my nearly 30 years of experience since then, never had either system fail me in an emergency. If LEO or FD need assistance, they have EMS in the back. If EMS needs help, TSHTF, and there ain't nobody left...