8 15 minutes and the user will have plenty of time to take appropriate action such as opening a window to raise the oxygen level the shape and location of the l shaped electrode 69 plays a substantial role in maintaining a steady flame in the location shown in fig4 b this electrode reduces the speed of gas flow and increases the duration of gas air mixing as well as the effectiveness of the mixing when prior electrodes such as those which are substantially s shaped are used and the oxygen level is 34 low 34 the flame tends to jump around from the position shown in fig4 a to the position shown in fig4 b such flame movement prevents accurate 34 low 34 oxygen level detection once the oxygen level drops to an 34 unsafe 34 level 18 5 to 18 7 or below the flame 92 will move to location shown in fig4 c here the flame is not in contact with or substantially close to either thermocouple and as a result the temperature of the second thermocouple 88 will also drop as will the voltage produced thereby the supply of gas to the burners and the pilot will then be cut off by the thermostat control valve 60 the progression described above should be distinguished from those instances where the heater is merely turned off when the heater is turned off the flame will move through the sequence shown in fig4 a to 4c and then completely disappear in a matter of seconds no 34 low 34 oxygen level signals will be provided when the heater is merely turned off.