A sufficient level of oxygen in the air we breathe is essential. Asphyxiants displace oxygen in the air. Breathing an oxygen deficient atmosphere can have serious and immediate effects, including unconsciousness after only one or two breaths. The exposed person has no warning and cannot sense that the oxygen level is too low.
If less oxygen is available to breathe, symptoms such as rapid breathing, rapid heart rate, clumsiness, confusion and fatigue can result. As less oxygen becomes available, nausea and vomiting, collapse, convulsions, coma and death can occur. Symptoms occur more quickly with physical exertion. Lack of oxygen can also cause permanent damage to organs including the brain and heart.
In addition to the suffocation hazard, some asphyxiant gases are also flammable. Some are compressed gases and can be combustible, easily catch fire, and burn or explode. Some gases are cryogenic and can cause serious burns. The SDS and the label on the container explains all the hazards for the materials you work with.