Photograph by EPA/Corbis

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Riot police wear gas masks in Bangkok, Thailand.

Photograph by EPA/Corbis

How Does a Gas Mask Protect Against Chemical Warfare?

In Israel, people are scrambling to get gas masks in case of a possible attack.

Hundreds of Israelis are lining up outside local distribution centers this week to collect protective gas masks following a series of reported chemical weapons attacks in Syria. If the United States does intervene in Syria, neighboring Israel fears being the target of a counterattack.

Speaking from the Department of State on Friday, Secretary of State John Kerry announced a death toll of 1,429 people from a Syrian chemical weapons attack, including at least 426 children. If Israel was caught up in this deadly chemical warfare, could gas masks provide effective protection to its people? (Realted: "Chemical Warfare, From Rome to Syria. A Time Line.")

To understand the workings behind a modern-day gas mask—an invention that dates back to World War I—National Geographic spoke with John Georgiadis, a professor of mechanical engineering at the University of Illinois, who researches filtration systems.

How is a gas mask made? Is it just like any other mask?

No. Assuming an attack is anticipated, a full-faced gas mask has two features that prevent us from inhaling potentially toxic contaminants in the air. They are barriers placed in the filter located on the snout of the mask.

The first is a particle filter which removes any bacteria in the inhaled air. There is essentially no chemistry involved here, just a physical barrier that forms a field between the toxins and the face. When a particle is inhaled, it hits the fibers on the filter and becomes tangled before it ever has the chance to reach the nose or mouth and move down to the lungs. (Related: "Why are Chemical Weapon Attacks Different?")

The second element is based on a chemical process called adsorption, and removes toxic molecules like the nerve gas sarin. Through adsorption, a solid or a liquid can trap particles on its surface—analogous to the way a cigarette filter reduces the amount of toxins a person inhales when smoking.

To filter out harmful chemicals, most gas mask filters are made with activated charcoal, or oxidized charcoal. When charcoal is activated with oxygen, it becomes ripped with tons of "sticky" holes in each molecular structure just like chicken wire. Any toxins that pass through the charcoal become bonded to these holes, and are prevented from moving into the gas mask.

How effective is a gas mask in a situation of chemical warfare?

For the full-face mask, a rubber hood goes over the head and creates a tight connection with the face. Sometimes people don't put it on properly and gas can then go through those cracks.

Many chemical attacks also affect the skin. Even if your lungs are protected by a gas mask, your skin is not. There are nerve toxins that are meant to attach themselves to the skin. Simply washing the skin is not sufficient for protection.

Can a filter become clogged?

There is a tricky compromise between creating an efficient filter that catches 99.99 percent of the toxic particles while also leaving enough open pores to breathe through. The masks are only meant to be worn for a short amount of time before the filter ultimately clogs up.

You could create a huge filter, but carrying it around would be like having an elephant trunk on your face. You wouldn't be able to move very easily.

How long can you wear a gas mask?

These are not engineered for long-term living, and you could probably wear a gas mask for about three to four hours before having to change the filter. You must be trained to get the mask on and off, change the filter, and expose yourself briefly to whatever chemical is in the air. I did this once, and don't want to do it again. It is a terrible feeling when you can't breathe because you are afraid.

This interview has been edited and condensed.

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