Which chemical is used in fire extinguishers? How is it harmful?

(N/A) The chemical commonly used in fire extinguishers,particularly in the past,is Chlorofluorocarbons $(CFCs)$ or Halons.
$CFCs$ are harmful because they are responsible for the depletion of the ozone layer in the stratosphere.
When these chemicals reach the upper atmosphere,they are broken down by ultraviolet radiation,releasing chlorine atoms.
These chlorine atoms react with ozone $(O_3)$ molecules,breaking them down into oxygen $(O_2)$,thereby thinning the protective ozone layer that shields the Earth from harmful ultraviolet radiation.