Rabbi Shmuel Eliahu was asked what a person should do if he sees an Arab starting a fire on Shabbat, (this is also true during the week too). Rabbi Eliahu responded: “Our Prime minister has declared these fires caused by arson as terror. Our intelligence agencies have declared this arson as a weapon of mass destruction. It was a miracle that nobody died from these fires but we don’t rely on miracles. To stop a fire on Shabbat, or an arsonist from starting a fire on Shabbat is permitted and is also a mitzvah. If necessary an arsonist may be shot. The IDF and the police must inform the public that the fires are not yet over. “
Normally one cannot put out a fire on Shabbat unless there is a risk of loss of human life. However, with the winds spreading the fires so quickly, the danger of loss of life is imminent and should be prevented.