While propane gas is not lethal in small doses, it can be fatal in high concentrations in poorly-ventilated areas. Inhaling it can cause a number of symptoms, including fatigue, nausea and collapse. Heavy physical activity may further induce symptoms due to a higher amount of inhaled gas.
Lower concentrations of propane gas may cause less severe symptoms, such as rapid breathing and fatigue. Symptoms become more severe as less oxygen becomes available due to the gas displacing oxygen in the lungs, which can eventually lead to death. Confined spaces filled with propane gas should be avoided until proper ventilation precautions are taken.