Wear safety glasses, set your work area up right, and ensure the area you are working on is a high enough temperature (be patient!). I started with a simple horizontal crack, and because I wasn't working at a high enough temperature the entire top half finely cracked into a fine spiderweb, and accompanied by a rainbow shower of extremely fine glass flakes. The showering glass flakes made me immediately reach for safety glasses, and the spiderweb yielded over an hour of fine tweezer-work and a finely scratched digitizer. I also highly recommend setting up your work area with the heat source suspended at an appropriate distance (so that the maximum temp is not above 200F) above your work area. With the heat source hands-free you can hold the phone with a gloved hand while gently working with your other hand.