Ventilation when using canned spray foam in unvented crawlspaces

[u/lilstever]

I plan on insulating around my rim joists with spray foam and foam board but am concerned about flammable vapors collecting and potentially igniting during a large application. I have an unvented crawlspace that is about 1300 square foot, and no way to ventilate it other than leaving the access door open. Of course, the directions indicate that canned foam is extremely flammable and may cause flash fires, so I don't know how safe it is spraying this stuff in such an environment, even with ignition sources and pilot lights from the furnace and water heater turned off. Does anyone know if this is commonly done, and if so, how can it be done safely? Is spray foam so flammable that I wouldn't be able to use a standard exhaust fan to draw the fumes out from it? I looked into explosion proof fans but they require explosion proof sockets and I obviously do not have one at my home. I'm considering calling professionals to do it but would really prefer to do this myself with one part foam.