Can i still become a firefighter if i have asthma?

Absolutely: Just like asthmatics can be olympic sprinters or swimmers, or anything else they want to be. The key is asthma control, not whether you have asthma or not. If a person's asthma is under excellent control, under the supervision of an allergist, then there should be nothing you can't do!

Bad idea: While it is a noble calling, you will be exposed to dense smoke, intensely hot dry air, dust, and ashes all of which can trigger your asthma and may lead to a life threatening attack. Since others are relying on you to be both a rescuer and a part of the team, getting taken out in the middle of action might make you a liability. Police work, medicine, etc are all still available...