Poisonous gas refers to any gas that can cause harm or death to living organisms when inhaled or absorbed. These gases can be produced by natural processes, such as volcanic eruptions, or by human activities, including industrial emissions and chemical spills. Common examples include carbon monoxide, chlorine, and ammonia, which can lead to serious health issues or fatalities. Exposure to poisonous gas can result in symptoms like coughing, difficulty breathing, and dizziness. In severe cases, it can lead to unconsciousness or death. Safety measures, such as proper ventilation and the use of protective equipment, are essential to prevent harmful exposure to these dangerous substances.