Say the word incinerator in Toronto, and you're likely going to hear an essay on environmental issues relating to it from some city dwellers. It wasn't that long ago waste was being burned in the city, however, in several locations; the Wellington Destructor was one of these trash-burning places in the city, working alongside one that used to stand at the Don Valley and Dundas, and another now closed plant in the city Portlands.
The term destructor was used to refer to incineration buildings at the time the plants were built; since then, incinerator has come to be the preferred term for newer buildings that handle this function. Not that there have been any new incinerators built in Toronto, however.
The Wellington Destructor was built after the conclusion of World War I to be a modern high temperature, forced draught incinerator. It was built to be the western downtown compliment to the aforementioned Don Destructor, which was built in 1917 to handle the waste from the eastern part of Toronto. Now closed, it's been put up for the historical building designation.
In terms of hazards, it's pretty much like any abandoned industrial site. Dead machinery, decaying structural components, etc. There's also a ton of pigeon shit in one room on the ground floor, so try not to spent too much time there. There's also a ton of garbage there, collected there by a person who used to take shelter there. There's also many cats living on the property, but I didn't see any of them.
Security wise, you're fine once inside. On the outside, it's surrounded by active houses and industries, and also has an active public works yard sitting next to it. There's also security cameras attached to the building; one appears to be covering the works yard while another covers the main ramp up to the building. No, you're not walking in the main door.
It's a pretty neat look into how the city used to be, and it's pretty interesting to take a look around if you can get in.