FORT JACKSON, SC -- A toxic chemical leak overcomes a driver and Soldiers in training.

A gunman is taken down after killing and wounding dozens of Soldiers and civilians at the 120th Adjutant General Battalion (Reception).

Those were the scenarios at Fort Jackson Monday during a mass casualty exercise that included participation from the installation, as well as emergency and law enforcement personnel from the surrounding community.

Aca,!A"The purpose of the exercise is to validate our procedures and practice our emergency response to a variety of circumstances,Aca,!A? said John Coynor, force protection officer. Aca,!A"Our goal is to make this post safer for the Soldiers, families and civilians.Aca,!A?

The exercise began around 9:30 a.m. when a vehicle transporting phosphine Aca,!" a colorless, toxic gas Aca,!" to Moncrief Army Community Hospital began leaking. The driver parked the vehicle near the NBC Chamber and was overcome by the fumes. Five Soldiers at the training site were also overcome.

A yellow smoke canister was used to simulate the leak and Soldiers participating in the exercise were put through the NBC chamber before emergency personnel arrived to simulate the effects of the gas.

After receiving a 911 call, an MP was dispatched to survey the site and emergency personnel donning protective suits went in to get the Soldiers and move them to a spot where they could be decontaminated with water by firefighters.

Halfway into the gas exercise, another 911 call came in to report a civilian gunman was shooting Soldiers at the 120th Adjutant General Battalion (Reception).

A perimeter was set up around battalion headquarters and first-responding law enforcement officers entered the building.

The suspect was shot and Special Response Teams went room to room, checking for other suspects. Meanwhile, wounded Soldiers were taken to a central location to be evaluated, treated and then interviewed by investigators. A seriously injured Soldier was airlifted to an area hospital and others were taken by bus ambulance for medical care.

Aca,!A"Terrorist tactics are changing ,Aca,!A? said Mark Mallach, installation antiterrorism officer. Aca,!A"Across the country we are seeing more and more active shooter cases. In the past, we would wait for the Special Response Team. Not anymore. As soon as we know a shooting is going on, we need to react as quickly as possible to save as many lives as possible.Aca,!A?

Normally, mass casualty exercises on the installation involve one scenario; however, organizers decided to make the most of the opportunity this time.

Aca,!A"Our limited budget allows us to do only one large-scale field exercise a year. So we put as much into it as we can,Aca,!A? Coynor said. Aca,!A"(Two scenarios) stresses our first responders and gives them a worst-case scenario to work with. It also gives our emergency operations center something to work out.Aca,!A?