Efforts to prevent poisoning include carbon monoxide detectors, proper venting of gas appliances, keeping chimneys clean, and keeping exhaust systems of vehicles in good repair. Treatment of poisoning generally consists of giving 100% oxygen along with supportive care. This should generally be carried out until symptoms are no longer present and the HbCO level is less than 10%. While hyperbaric oxygen therapy is used for severe poisonings, the benefit over standard oxygen delivery is unclear. The risk of death among those affected is between 1 and 30%.