Control the hair and you control the head.
Control the head and you control the body.
Stupid policy to not understand that.
The respirator argument is silly...just say its unfair to WOMEN, many of who cannot grow beards.
Women can have beards....
Any guard should be able to refuse to serve with any other guard who can't use his assigned equipment properly and that includes the gas mask.
Both prisoners and other guards who are injured in a situation where the guard with the beard succumbed to tear gas or refused to enter a situation because they would succumb to tear gas, should sue the prison system and the guard individually for intentionally failing to meet known standards.
A guard with a beard needs to sign a waiver explicitly stating, "If you succumb to tear gas, we are NOT risking other guards' lives to rescue you." Their deity can save them.