One who lights a fire of any size that meets some need violates a Torah prohibition. It makes no difference whether he starts the fire by rubbing stones together, using a magnifying glass to focus the sun’s rays on straw, lighting a match, or turning on the electricity. It also does not matter if the fire is fueled by oil, kerosene, or electricity. Anytime one intends to start a fire and succeeds in doing so, he transgresses a Torah prohibition.
However, one who merely causes sparks to be released does not violate Torah law. Furthermore, if the sparks were released unintentionally, there is no prohibition at all. Therefore, one may wear woolen or synthetic clothes, even though sometimes sparks are released when putting them on or taking them off. Since these sparks are released unintentionally and to no purpose, there is no prohibition (SSK 15:76; Yeĥaveh Da’at 2:46).
Just as it is prohibited by Torah law to kindle a new fire, it is also prohibited by Torah law to increase a pre-existing flame. The law on Yom Tov is different; while one may not kindle a new fire then either, one may turn up an existing flame. On Shabbat, however, one may not even raise a flame. For example, one may not increase the flame on a gas burner by turning the knob controlling the gas flow. Likewise, one may not increase the flow of kerosene to a heater in order to raise the flame or add oil to a burning lamp on Shabbat (Beitza 22a).
Similarly, one may not stoke coals, since this intensifies the fire (Kereitot 20a). Likewise, one may not open the door of a wood-fired oven because doing so allows air to enter the oven and fan the embers, thus increasing the fire (MB 259:21). If the oven door is already open, or there is a fire in an enclosed area (such as a fireplace), one may not open a window or door facing the fire, because a strong wind may enter and fan the flames. If there is no breeze, one may open the door or window (SA 277:2).
While an oil lamp is on a table, one must try to avoid shaking the table, because the oil may move closer to the wick and increase the flame, a violation of Hav’ara. However, if it is a wax candle on the table, or if the oil lamp has a floating wick, he does not need to worry that shaking the table will cause the flame to increase (MB 277:18).
