The glass ampule is snapped open by
- orienting the dot (or other marker for the site that has been scored) away from yourself and
- pulling the top and bottom of the ampule toward you while pushing the neck of the ampule away from yourself (with your thumbs).
Since the edge of broken glass can be sharp and jagged, you should take precautions to avoid cutting your fingers. Keeping your thumbs and fingers away from the neck of the ampule when it is snapped open or wrapping the neck with an alcohol pad are generally effective.