On the Night of the Zombie Apocalypse, I Was Still Working Overtime at the Machine Factory

The night when the zombie apocalypse broke out, the whole city fell into hell on earth. Only we, a group of unlucky workers who were forced to work overtime all night by our boss, managed to survive. I am a versatile technician in the factory area, taking over the factory overnight. I have no special powers and do not rely on the system. We workers only rely on ourselves! All technicians build hard-core infrastructure and defend the only steel fortress in the wasteland!