Permissible to break Salat
1) Urge to pass urine or stool.
2) Snake, Scorpion or some other harmful creature makes appearance.
3) Fear of missing a train
4) Fear of thief taking away shoes or valuable
It is Wajib to break one's Salat in order to answer a parent or a grandparent who has called out in distress. Nevertheless, it is not necessary when someone is around to assist.
It is Fard to break one's Salat when it is feared that a blind person would fall into a pit or a well if he is not stopped. It is Fard to break one's Salat when some person has caught on fire and requires assistance.
These images are for Illustration only. Please see the following book for reference
Talimul Haq (Hanafee) by Shabbir Ahmad E Desai