The Medi-Militant group writed a quick guide for protester giving advise and tricks in cas of chemical-weapon usage byt the police force (peper spray and tear gas). The guide also content some tips in anticipation of a demo and the neccesity of medic intervention.
Info on the group : Create at the heart of the 2012 Quebec Student's Strike, the Medi-Militant has an objectif to give medical care to protesters, victims of a increasing police brutality.
You can have acces to the guide here. It's also printable.