Is it common for civilians to be running around with CS spray (tear gas) on their person in the UK? Carrying OC spray (pepper spray) is extremely common here, but not even police would be carrying CS unless heading to a riot situation. OC seems to be the tool of choice for routine police work. Unlike OC, CS usually comes in a rather large canister that I would think would be inconvenient to conceal.
I've never had the "pleasure" of being subjected to CS, but I've had plenty of dealings with OC in an enclosed space and it can linger for a surprising amount of time. I can see how a canister of OC could be discarded, then heavier items get placed in the bin which causes the discharge spray button to get pressed. A fogger-type spray would create plenty of dispersal even from the bin. The physical symptoms are not exactly pleasant even walking into a room 15+ minutes after a spray. All it would take is a few easily excitable pax and it turns into mass hysteria. But again that's OC. Maybe CS is similar.