A silent killer invades a St. Joseph family`s home and sends two people to the hospital. Emergency responders say the victims are very lucky tonight after a close call with carbon monoxide. "The wife was taken to St. Luke`s Hospital yesterday because of this and now the little girl is out here," Captain Dennis Dornhoffer with the St. Joseph Fire Department says. The culprit? Carbon monoxide. Dornhoffer says it`s one of the worst cases of carbon monoxide saturation he`s seen, where the family has lived to tell about it. "There`s a possibility that a water pipe broke inside the hot water heater, flooded it all out, blew the pilot light out, and the gas kept building up, building up, building up," Dornhoffer says. Missouri Gas Energy recommends evacuating a home if CO levels climb above 33 parts per million. The fire department found lethal levels seeping out of a hot water heater. "We had about 300 plus parts per million, which is extremely, extremely dangerous. This has been going on for the last couple of days," Dornhoffer says. Fire fighters say a carbon monoxide detector would have sounded warning bells earlier, had the family only plugged it in. "He had it in the garage--a brand new one, and as soon as he opened it up and put the batteries in, it went off," Patrolman David Loyd with the St. Joseph Police Department says. Lying cooped up inside a house for days on end, carbon monoxide can be a silent killer, laying low until it`s too late. "It builds up in concentration as it rises, so by the time it gets up to the level where people are breathing it, it`s usually a higher concentration," Loyd says. "You can`t smell it or see it, you can`t taste it, you can`t detect it at all." Including the poisonous gas` symptoms... "Dizziness, nausea, vomitting, sleeping a long time, your muscles tend to get relaxed, you`re just lazy," Dornhoffer describes. It sounds like the common flu but could be much worse. Fire fighters say Candy Hinkley, who may go by a different last name, was treated for carbon monoxide poisoning overnight at St. Luke`s Hospital in Kansas City. Her 12-year old daughter Lacy Hinkley was taken to Heartland Regional Medical Center around 10 this morning but also has been treated and released.