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