An apparatus 8 and further comprising a second shutoff valve in said exhaust line between the connection to said oxidizing gas line and said {HEAD ~ outlet}, said second shutoff valve having a control input connected to {TAIL ~ said level sensor} 
An apparatus 8 and further comprising a second shutoff valve in said exhaust line between the connection to said oxidizing gas line and said { HEAD ~ outlet } , said second shutoff valve having a control input connected to { TAIL ~ said level sensor }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL