The most frequent cause of home gas poisoning is carbon monoxide, a poison capable of producing unconsciousness and death even when it is present in the air in very low concentrations. It is not readily detectable by the sense of smell or taste because when it is pure, it is colorless, odorless, tasteless, and non-irritating. Carbon monoxide poisoning often occurs with no more symptoms than a slight headache or muscular weakness, and even these may not be noticeable unless the victim starts to move or exercise. He soon becomes helpless with unconsciousness and death following. Carbon monoxide is formed when solid, liquid, and gaseous fuels are burned with an insufficient air supply and it is present in high concentration in manufactured illuminating gas. The danger of monoxide poisoning is increased by cold weather because of the increased use of fuel and reduced ventilation in the home. Gas-burning equipment that is improperly installed and adjusted or which is used carelessy is dangerous. A gas flame should have a good air supply. Liquids boiling over the edge of a pan, or a very large container placed on the burner can cause incomplete combustion of the gas or extinguish the flame completely. An exploring child or someone falling against the stove may turn on a gas jet. Any movement of a gas appliance with a rigid gas connection can cause a joint to leak. Natural gas and bottled "liquid petroleum" gas are classified as "nontoxic" and there is little danger from asphyxiation when they escape unburned. These fuels cannot be used