Is working in Civil Defense permissible or forbidden, and what is the legitimate proof for that?

All permissible jobs are lawful unless they involve a Sharia-forbidden act or assistance in sin. The work of civil defense is among the righteous deeds due to the great benefits it entails, such as extinguishing fires and aiding the distressed. Some of these duties may even take precedence over congregational prayer or prayer at its prescribed time when necessity dictates.