How deadly would chemical weapons in Syria be?

Serious concerns have been raised about chemical weapons in Syria as unnamed US officials on Wednesday told NBC News that Syrian forces have loaded sarin, a deadly nerve gas, into bombs that can be dropped by planes.

The officials said the bombs had not been loaded onto planes and there was not yet a decision from Syria's leader to use them.

President Obama has said the use of chemical weapons in Syria is a “red line” that would draw the US into the war. Embattled Syrian President Bashar al-Assad has denied that he’s planning to use them, unless international forces intervene. And Syrian officials have called recent accusations a “pretext for intervention.”

The international community is now debating if and how to respond to this latest development.

As the situation unfolds, for many unfamiliar with sarin gas there may be some question as to what it is and just how deadly it can be. Though it’s classified as a weapon of mass destruction and is extremely lethal, it is not in the same league as nuclear weapons.

“Chemical weapons are not nuclear weapons. In order to produce a lot of damage they have to be distributed very efficiently. The problem with them is that they can be very deadly and efficient if used in population centers and their effects are indiscriminate,” says Daryl Kimball, executive director of the Arms Control Association.

“The explosion of a single chemical shell would not necessarily be a catastrophe if it went off accidentally at one of these storage sites, but the deliberate use of one chemical shell in a population center could be very deadly,” adds Mr. Kimball.

Sarin is a colorless and odorless nerve agent that can be attached to missiles and artillery rounds and is primarily lethal when inhaled but can also penetrate skin and clothing.

It evaporates quickly, though under the right conditions it can linger for up to five days. As a result, a sarin attack requires little clean up and areas affected by sarin can be quickly reoccupied, making it a desirable weapon for military units looking to advance without destroying infrastructure and equipment.

It was first developed in Germany in 1938, but there was no known use of it as a weapon, until 1988 when Iraq used it against the Kurdish town of Halabja. The Iraqi military is also believed to have used sarin against Iran during the war between the two countries that spanned from 1980 to 1988.

Most recently, it was used by the Japanese group Aum Shinrikyo which manufactured their own form of impure sarin gas and released it on the Tokyo subway in 1995. The attack killed 12 and injured at least 5,500 people.

It’s unclear exactly how much damage would be caused were Syrian jets to drop bombs filled with sarin gas on an apartment block or populated area, but experts say the attack would likely be lethal and devastating, creating a major impact.