Offer help, without using force.
If victims are combative in trying to flee from the hot zone, lather them up with soap spray to help them get clean, rather than using guns to shoot over their heads, or pepper spray to force them back.
Make it clear that the soap spray is a form of rescue, and not a form of non-lethal weaphon.
Imagine yourself covered from head to toe in a very gentle baby shampoo. You can't really fight, or flee. What is more likely is that you will cooperate with some gentle guidance toward the decontamination showers.
The containment would be incidental. For example, doors would automatically lock or unlock ("emergency exit unlocked by fire alarm") and escalators would automatically switch to a unidirectional mode (i.e. they would all go in the same direction) to gently herd everyone toward washbuses or the subwash system.
Firmware in elevators and escalators is modified so that in an emergency the evacuation and containment is automatic, and does not involve the use of human police or soldier forces.
It is much less likely that individuals will become politically polarized, if the architecture simply guides them to a rescue and decon area, than if foot solders or police use force to maintain a cordon or quarantine a "hot zone".
Flex cuffs should never be used at a riot scene, because there may be some innocent bystanders (or journalists) who just happened to be walking through the area, who get swept up in a mass arrest. Instead, a mass-rescue that is both gentle, yet impossible to exit from, can be constructed by way of architecture, and infrastructure. Everyone is treated kindly, and force is never used. No distinction need be made in the treatment of a perpetrator, a bystander, or a journalist. All are rescued, decontaminated, and contained using destraint rather than restraint. The decontamination process leads to discovery (weapons or other evidence found in clothing, etc.) and eventual capture and detention of the perpetrators, without offending innocent bystanders who happened to be in the wrong place at the wrong time through no fault of their own.
A solid containment boundary exists by design, without any perceived or actual intention to use force.
--S. Mann, DECONference 2002