Pull ups are very beneficial, but you should take into account the following safety reminders in order to avoid injury.

1. Do Not swing or bounce when using your pull up bar.
2. Do Not attempt to hang by your feet or legs from your pull up bar.
3. Do Not use a doorway pull up bar if you weigh over 300 lbs.  Try a pull up station instead.
4. Do Not use a doorway pull up bar if you are unsure about the stability of the doorway or door jamb.
5. Do Not allow children under 18 years of age to use a doorway pull up bar unless supervised by an adult.
6. Ensure that you test to make sure your pull up bar is completely secure in the doorway before using it.
7. Make sure you maintain a controlled motion when performing pull ups or chin ups.

Pull ups and chin ups are great at-home exercises, but you need to take these precautions to ensure that you avoid injury.  Now get back to your workout and add some reps!