spray foam personal protection
There is an expanding foam product made specially for injection into stud wall cavities. I don't think standard "spray foam" insulation is appropriate for injection into an enclosed cavity. Generally spray foam is applied to exposed surfaces. At any rate, in terms of the required personal protective equipment, you should be able to get a hold of a MSDS (material safety data sheet) for the product you are considering, either from the vendor or from the manufacturer. It will list the required personal protective equipment. This may vary from one type of foam to another.

For enclosed walls, you might consider blown-in cellulose insulation. This is a common choice for retrofit applications.