A gas mask is a special face covering designed to protect someone from breathing in dangerous substances in the air. It fits tightly over your nose, mouth, and often your entire face, with a filter that cleans the air before you breathe it in.

Gas masks were invented in the early 1900s and became crucial during World War I, when armies used poison gas as a weapon. Soldiers wore gas masks to survive these chemical attacks. The masks had round glass eyepieces so soldiers could see, and a canister attached to the mask that filtered out deadly gases.

Today, firefighters wear gas masks when entering smoke-filled buildings, since smoke contains poisonous gases that would quickly overcome anyone breathing normally. Scientists working with hazardous chemicals wear them in laboratories. Emergency workers might need them during industrial accidents when toxic fumes leak into the air.

The filters in gas masks work differently depending on what they're protecting against. Some use charcoal to absorb chemicals, while others have special materials that block tiny particles. A gas mask designed for smoke won't necessarily protect against other dangers, which is why professionals choose specific masks for specific situations.

During the Cold War, many governments distributed gas masks to citizens in case of attack, and some countries still keep them in emergency supplies. While most people will never need to wear one, gas masks remain an important safety tool when the air itself becomes dangerous to breathe.