The Occupational Health and Safety Act gives most workers the right to refuse work if the physical conditions of the workplace are likely to endanger them [Section 43(3)(b)], You must make sure that your students are in a safe place before going to the administration.
A worker simply needs reasonable belief that they are unsafe or there is a danger to them.
There are more stages to the process, but this is the general cycle that will take place. Making a work refusal can be scary or you might worry that you're "doing the wrong thing". Nobody can tell you that you "should feel safe". Only you know how you feel.
Step #1: Ensure that students are safe. Teachers cannot leave students unsupervised.
Step #2: Report the situation to your supervisor (principal). Call your administration to let them know you feel unsafe and are invoking your right to refuse unsafe work.
Step #3: Remain in a safe place for the investigation to unfold. A person cannot go home after starting the work refusal. They should go to a space where they feel safe. Union representation will join the person soon to move through the process. The investigation will involve several different people (ex. principal, possibly special education principal, union member, etc.). The investigation should be a process to understand why the member feels unsafe and work towards finding solutions.
Step #4: Return to work once the investigation concludes, if you feel safe.
The Ministry of Labour is not always in attendance of these work refusals. Many work refusals are resolved at the school level without having to be referred to the Ministry of Labour. Also, following a work refusal, if the member starts working again and feels unsafe, they can refuse unsafe work again. This is not a "one and done" situation.
A union representative will be with you each step of the way. Find more details from the OSSTF website.