Let me first of all commend you and your colleagues for your dedication. The same is true for all those who willingly put their lives on the line so we can live in safety and freedom. Our world is a better place because of you, and God has given you a very important responsibility.
I don't know why your fellow firefighters aren't interested in God and refuse to give any thought to eternity; why don't you ask some of them? One answer may be that they have always prided themselves on being strong and self-reliant - and they think it would be a sign of weakness to turn to God. But that isn't true; it takes courage to admit we need God in our lives.
Another answer (at least for some of them) might be that they secretly hope God will reward them and let them into heaven because of all the good things they do for others. But this isn't what the Bible teaches, because only Christ can save us from our sins and give us the new life we need. The Bible says, "Salvation is found in no one else, for there is no other name under heaven given to men by which we must be saved" (Acts 4:12).
Pray for those you work with - and pray too that God will help you be a witness to Christ's love by the way you live. Jesus said, "Let your light shine before men, that they may see your good deeds and praise your Father in heaven" (Matthew 5:16).