Sodium carbonate is a noncombustible substance. As such, unlike many organics, it does not have a flash point.
Sodium carbonate is not especially toxic, but it's still an irritant. Wash with plenty of water. In case of eye exposure, contact an eye specialist, because trace sodium carbonate can become lodged under the eyelid.
Because sodium carbonate rarely reaches lower respiratory tracts, casual exposure is not considered dangerous to the average person. However, excessive amounts will cause irritation and discomfort.
The substance is basic in aqueous solution. The carbonate ion attracts H+ ions in neutral water to form HCO3[1-] ion, shifting aqueous equilibrium toward an excess of OH- ions.
Due to basic aqueous chemistry, environmental impact of sodium carbonate is a function of, in part, local natural pH buffer capacity.