An objection to the use of industrial-type respirators for protection against COVID-19 (as opposed to, for example, the dusts for which they are designed) is that the user exhales through an exhaust valve that offers little or no protection to others. This is probably why such respirators can be purchased, as health care workers might not be able to use them (as they do not protect the patient). This issue can be dealt with, however, by placing a surgical or cloth mask over the exhaust valve.
This emphatically does not constitute engineering or OH&S advice because, just to begin with, this procedure is not mentioned in the respirator’s instruction manual but my own experience is that the cover resulted in little if any difficulty in exhaling.
