Is extreme fatigue and thirst while working during the daytime in Ramadan considered a valid excuse for breaking the fast, and what are the implications of that?

If the thirst is severe and difficult to bear, then it is permissible to break the fast, and there is no sin upon the fasting person. It may even be obligatory to break the fast if one fears perishing. This day must be made up. So, whoever is overcome by hunger and thirst and fears perishing, it is obligatory for them to break the fast.