Praise be to Allah.
If someone breaks the fast due to extreme thirst, because he feared that he might die or suffer severe harm, or he was not able to complete the fast because of extreme hardship, then he must refrain from eating and drinking for the rest of that day, and it is not permissible for him to eat or to drink too much; rather he may drink enough to ward off harm, then he must abstain until sunset. He also has to make up that day’s fast.
It says in Kashshaaf al-Qinaa‘ (2/310): Abu Bakr al-Aajurri said: In the case of one whose job is hard, if he fears that he may die because of fasting, he may break the fast and make it up, if giving up his work will cause him harm. But if giving up his work will not cause him harm, he is sinning if he breaks the fast, and he should leave that job. Otherwise, if giving up the job will result in harm, then there is no sin on him if he breaks the fast for a valid reason. End quote.
It says in Fataawa al-Lajnah ad-Daa’imah (10/233): It is not permissible for the accountable person to break the fast during the day in Ramadan just because he is working. But if he is subject to a great deal of hardship that leaves him no choice but to break the fast during the day, he may break the fast by eating or drinking as much as will reduce the impact of the hardship, then he must refrain from eating and drinking until sunset, then break the fast with the people. And he must make up that day on which he broke the fast. End quote.
Shaykh Ibn Baaz (may Allah have mercy on him) was asked: Some people break the fast for various reasons, such as experiencing extreme thirst, for example, and if they break the fast they continue not fasting, by eating and drinking, and they regard it as permissible to eat all kinds of food. What must one do in such a situation?
Answer: It is not permissible for him; rather he should break the fast only as much as is needed, so he should drink then stop, if the issue is thirst, or he should eat only as much as will keep him going, if he broke the fast because of hunger; then he should refrain from eating and drinking until the sun sets, and he should not carry on breaking the fast. He has only eaten and drunk on the basis of necessity, then after that he should continue fasting. The same applies in the case of someone who wants to save someone else from drowning or from an enemy, and is not able to do that unless he breaks the fast, in which case he should break his fast and save his brother. Then he should refrain from eating and drinking until the sun sets, and he must make up that day only, because he broke the fast for a necessary reason, because saving the life of his brother whose life is sacred according to Islamic teachings is obligatory.
End quote from Fataawa Noor ‘ala ad-Darb (16/164).
And Allah knows best.