Bad answer:

I like firefighting. I think it is really cool.

Do not just say you like it. Anyone can like firefighting. Focus instead on your history with the industry and if you can, tell a story.

Good answer:

I have always appreciated and admired those who put their lives on the line to protect our comminutues. My interest really piqued in firefighting however after I witnessed a post-crash rescue. I heard the calling as I watched the first response team pull the civilians to safety and out of harms way. It was then I knew that this is what I was meant to do.