I’d like to become a firefighter but recently signing up for my college classes I realized to become a firefighter in United States you need to be ‘Clean Shaven’ at all times. The only thing allowed is a short mustach that is because the mask seal can’t stick to a beard and mask seal is required to avoid the toxic chemicals entering your system. Is it permissible to shave my beard?

It still would not be permissible. Try to get a religious exemption, if possible.

Having said that, if the toxic chemicals will harm you, and there is a shortage of firefighters, then yes you can shave your beard to protect yourself.