ISIS Shell Fired at US Base in Iraq Being Checked for Mustard Agent, US Official Says

Further testing being done, no one injured, officials said.

The American base at Qayarrah West Airfield received some indirect fire on Tuesday afternoon, according to the military official. Hundreds of American personnel are currently working on the airfield to prepare it as a logistical hub for an eventual offensive on the ISIS-held city of Mosul. No one was injured in the rocket attack.

Following the attack, a small team of U.S. personnel conducting a routine inspection for unexploded ordnance in the perimeter around the base came across a small shell fragment that contained what the official described as an oily "tar-like" residue, which sometimes indicates mustard agent.

A chemical field test of the shell fragment tested positive for mustard agent, but a subsequent test came up negative, the military official said. The shell fragment will now undergo further testing at a laboratory to determine if it ever contained the blistering agent.

As a precautionary measure, the two to four U.S. military personnel who came across the shell fragment were decontaminated with showers and brushing to wipe away any agent, the official said. None of them has shown any symptoms or potential impacts from the contact with the shell.

Mustard agent is a powder that can be placed in the hollow tip of an artillery shell or rocket. Exposure at a place of impact could cause blistering, but the agent dissipates quickly and does not spread over a wide area.