question about volunteering

I am a new grad and I have 10 months experience working on a stroke/neuro unit. I have to work full time but would love to volunteer. My question is if I wanted to volunteer in a place of disaster like Haiti where nurses are needed at a moment's notice would my hospital hold my job for me? I would really love to volunteer but I need an income when I come back.

Has anyone else volunteered to go to Haiti who works a full time?

Thanks in advance..