First you will need to talk to your immediate supervisor, let him know what’s going on and try to find his approval. Have an agreement or plan on who to hand out your projects/duties. Establish a good communication with your partners so there’s no doubts or questions on how to handle your tasks while the emergency leave is in effect.
Once you do this, write your letter and hand it off to the Human Resources department. Make sure you include in your letter that you have already talked to your supervisors and team mates.