This is harder than I thought it would be to answer.
Federal OHS Regs. address hot work IN CONFINED SPACES. The relevant requirement:
Hot Work
11.9(2) Where hot work is to be performed in a confined space that contains concentrations of flammable or explosive materials in excess of the concentration set out in paragraph (1)(a) or (b), (a) a qualified person shall patrol the area surrounding the confined space and maintain a fire-protection watch in that area until all fire hazard has passed; and

But there’s no corresponding specific requirement for fire watches for hot work outside confined spaces with explosive atmospheres. Of course, that doesn’t mean they’re NOT required. The part of the Regs. you’d have to look at, though, would be Part XIX requiring employers to implement a Hazard Prevention Program to assess hazards and select appropriate measures to control them, including engineering controls, work controls and PPE. Fire watches would be an example of a work control that would presumably be necessary to deal with temporary hot work areas.
Moral of the story is that the OHS Regs don’t specifically address each and every possible situation and required control. They just put the onus on the employer to do so in the course of operations, like when they’re setting up a temporary hot work area. As a result, you won’t always be able to cite a specific section of the Regs. that says you need to use a particular safety measure even though NOT using that measure would still be considered a violation.
Hope that makes sense and check back with me if it doesn’t and I’ll be happy to explain. glennd@bongarde.com Glenn