If you don't have a pair of scissors, check around for other deadly office supplies. For example, throw a "three hole paper punch", ink cartridge, make a paper "drone" out of a DHS "memo", fly it right into the shooter. take him/her out quick.
Hit them with a roll of duct tape. (Esp effective on chemical warfare- from a previous DHS memo - hold the plastic) Oh wait.... pop a plastic bag - sounds like gunfire .